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الرئيسية A comprehensive treatise on inorganic and theoretical chemistry. F, Cl, Br, I, i, Na, K, Rb, Cs
A comprehensive treatise on inorganic and theoretical chemistry. F, Cl, Br, I, i, Na, K, Rb, CsMellor J.W.
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A COMPREHENSIVE TREATISE ON INORGANIC AND THEORETICAL CHEMISTRY VOLUME II F, CI, Br, I) Li, Na, K, Rb, Cs Works by J. W. MELl.OR, D.Sc., F.R.S. A COMPREHENSIVE TREATISE ON INORGANIC AND THEORETICAL CHEMISTRY. In Thirteen Volumes. Royal8vo. VoL I. II, O. With 274 Diagrams. £3 3s. net. Vol. II. F', CI, Er, I, Li, Na, K, Rb, Cs. With 170 Diagrams. £ 3 3 s . net. Vol. IlL Cu, Ag, Au, Ca, Sr, Ba. With 158 Diagrams. £3 Jr. net. Vol. IV. Ra and Ac Families, Be, Mg, Zn, Cd, Hg. With 232 Diagrams. £3 3s. net. . Vol. V. B, AI, Ga, In, 1'1, Se, Ce, and Rare Earth Metals, C (Part 1.) With 206 Diagrams. £3 3s. net. Vol. VI. C (Part 11.), Si, Silicates. With 221 Diagrams. £3 3s. net. Vol. VII. Ti, Zr, 11f, Th, Ge, Sn, Pb, Inert Gases With 255 Diagrams. £3 3s. net. INTRODUCTION TO MODERN INORGAr\IC CHEMISTRY. With 232 Diagrams. Crown 8vo, 9<. net. MODERN INORGANIC CHEMISTRY. With 369 Diagrams. Crown 8vo, 12S. 6d. net. HIGHER MATHEMATICS FOR STUDENTS OF CHEMISTRY AND PHYSICS. Withspecialreference to Practical Work. With 189 Diagrams. 8vo, 21s. net. TilE CRYSTALLISATION OF IRON AND STEEL: an Introduction to the Study of Metallography. With 65 Illustrations. Crown Evo, Ss. 6d. net. LONGMAl\'S, GREEN AND CO., LTD. LONDON, NEW vonK, TonONTO, CALCUTTA, BOMBAY, AND MADRAS. A COMPREHENSIVE TREATISE ON INORGANIC AND THEORETICAL CHEMISTRY BY J. W. MELLOR, D.Se., F.R.S. VOLUME II WITH 170 DIAGRAMS SECOND h'vIPRESSION ;?u,- 7 LON G MAN S, G R E E NAN D CO. 39 PATERNOSTER ROW, LONDON, KC.4 NEW YORK, TORONTO CALCU'lTA, BOMBAY AND MADRAS 19 2 7 _ / .? .3 .? LTD. A /J rights reser'Jt<J CONTENTS PAGE ABBREVIATIONS . I . . . . . . . . . . , . II . . . . . . . . Vll CIIAPTER XVII THE HALOGENS * 1. The Occurrence of Fluorine (1); 2. The History of Fluorine (3); Ii 3. The Preplua. tion, of Fluorine (7); 4. The Properties of Fluorine (9); '5. The Occurrence of Chiorine, Bromine, and Iodine (15); 6. The History of Chlorine, Bromine, and Iodine (20); 7. The Preparation of Chlorine (25); Ii 8. The Preparation of Bromine (38); Ii 9. The Preparation of Iodine (41); 10. The Physical Propertics of Chlorine, Bromine, alld Iodine (46) ; 11. Solutions of Chlorhle, Bromine, and Iodine in Water, etc. (71); 12. Chemical Reactions of Chlorine, Bromine, and Iodine (90); 13. Colloidal Iodine and Iodized Starch (98); 14. The Atomic Weights of Chlorine, Bromine, and Iodine (101); 15. The Colour of Solutions of Iodine (110) ; 16. Binary Compounds of the Halogcns with One Another (111:1). CHAPTER XVIII THE CO:\lPOUNDS OF THE HALOGENS WITH HYDROGEN 9 1. The Preparation of Hydrogen Fluoride and Hydrofluoric Acid (127); 2. The Properties of Hydrogen Fluoride and Hydrofluoric Acid (129); 3. The Fluorides (137) j 9 4. Equilibrium, and the Kinetic Theory of Chemical Action (141); 5. The Union of Hydrogen and Chlorine in Light (148); g 6. The Preparation of Hydrogen Chloride and Hydrochloric Acid (158); 7. The Preparation of Hydrogen Bromide and Hydrobromic Acid (167) j Ii 8. The Preparation of Hydrogen Iodide and Hydriodic Acid (170); 9. The Physical Properties of the Hydrogen Chloride, Bromide, and Iodide (173); 10. Properties of Hydrochloric, Hydrobromic, and Hytlriodic Acids (182); U. The Chemical Propertics of the H.ydrogen Halide and the Corresponding Acids (200); \I 12. The Chlorides, Bromides, and Iodides (214); 9 13. Colour Changes on Heating Elements and Compounds (221); 14. Double and Oomplex Salts (223); 15. Double Halides (228); 16. PerhaliJes or Polyhalides (233). v VI OONTEN1'S CHAPTER XIX THE OXIDES AND OXYACIDS OF CHLORINE, BROMINE, AND IODINE S 1. Chloride Monoxide (240); S 2. The Preparation of Hypochlorous, Hypobromons, and Hypoiodous Acids (243); 9 a. The Properties of the Hypohalous Acids and their Salts (250); S 4, Bleaching Powder (258); S 5. The Hypochlorites, Hypo- bromites, and Hypoiodites (267) j 9 6. Electrolytic Processes for the Preparation of Hypochlorites, Hypobromites, and Hypoiodites .(276); S 7. Chlorine, Bromine, and Iodine Trioxides j and the Corresponding Acids (281); 9 8. Chlorine Di- or Per-oxide (286); S 9. Iodille Di- or Tetra-oxide (291); S 10. The Halogen Pentoxides (293); S 11. The Preparation of Ohloric, Bromic, and Iodic Acids, and of their Salts (296) ; S 12. The Properties of Chloric, Bromic, and [odic Acids and their Salts (305); S 13. The Halogenates-Chlorates, Bromates, and Iodates-of the Metals (324); S 14. Perchloric Acid and the Perchlorates (370); S 15. Perbromic Acid and the Perbromates (384); 16. Periodic Acid and the Periodates (386) ; 17. The PQrchlorates (395); S 18. Periodates (4.06). CHAPTER XX THE ALKALI METALS 1. The History of the Alkali Metals (419); 2. The Occurrence of the Alkali Metals (423); 3. The Potash Salt Beds (427); S 4. The Extraction of Potassium Salts (436); S 5. The Extraction of Lithium, Rubidium, and Cresium Salts (442); S 6. The Preparation of the Alkali Metals (445); S 7. The Properties of the Alkali Metals (451); 8. The Binary AJIoys of the Alkali Metals (478); 9. The Hydrides of the Alkali Metals (481); 9 10. The Oxides of the Alkali Metals (484) ; S 11. Hydroxides of the Alkali Metals (495); 12. The Alkali Fluorides (512) ; S 13. Ammoninm Fluoride (519); S 14. The Alkali Chlorides (521); S 15. The Properties of the Alkali Chlorides (529) ; S 16. Ammonium Chloride (561) ; S 17. The Alkali Bromides (577) j S 18. Ammonium Bromide (590); S 19. The Alkali Ioo.itles (598); S 20. Ammonium Iodide (615); S 21. The Alkali Monosulphides (621); S 22. The Alkali Polysulphides (629); S 23. The Alkali Hydrosnlphides (841) j S 24. Ammonium Sulphides (645); S 25. The Alkali Sulphates (656) j S 28. Alkali Acid Sulphatcs; Alkali Hydrosulphates (677); S 27. Ammoninm Sulphates (894) ; S 28. The Occurrence and Preparation of the Alkali Carbonates (710) ; S 29 The Manufacture of Soda by N. Leblanc's Process (728) ; S 30. The Ammonia-Soda or E. Solvay's Process (737) ; S 31. The Properties of the Alkali Carbonates (747); S 32. The Alkali Hydrocarbonates, Bicarbonates, or Acid Carbonates (772); S 33. The Ammonium Carbonates (780) j S 34. Carbamic Acio. and the Carbamates (792); S 35. Commercial "Ammonium Carbonate" (797); 36. The Alkali Nitrates (802) j S 37. Gunpowder (825); S 39. Ammonium Nitrate (829); S 39. Normal or Tertiary Alkali Orthophospbates (847); S 40. I:)econdary Alkali Ortbophosphates (851); S 4.1. Primary Alkali Orthophosphates (858); S 42. Alkali Pyrophosphates or Diphosphates (862); S 43. Alkali Metal phosphates (887); S 44. Ammonium Phosphates (871); S 45. The Relation between the Alkali Metals (879). INDEX. . . . . . . . . ... ... . . . . . . . . . . . . . . 881 ABBREVIATIONS Aq. = aqueous atm. = atmospheric or atmosphere(s) at. vol. = atomic voIume(s) at. wt. = atomic weight(s) TO or oK = absolute degrees of temperature b.p. = boiling point(s) °Il = centigrade degrees of temperature coeff. = coefficient conc. = ooncentrated or concentration dil. = dilute eq, = equivalent(s) f.p. = freezing point(s) m. p. = melting point(s) mol ( s) = { gram-mOlecule(S) gram-molecular I ( ) { mOleCUle(s) mo S.= molecular mol. ht. = molecular heat(s) mol. vol. = molecular volume(s) mol. wt. = molecular weight(s) press. = prcssure(s) sat. = saturated soln. = solution(s) sp gr. = specific gravity (gravities) sp. ht = specific heat(s) sp. vol. = specific volume(s) temp. =: temporature(s) vap. = vaV;)Uf vii CHAPTER XVII TIlE HALOGEN 8 1. The Occurrence of Fluorine T HE four elements fluorine, chlorine, bromine, and iodine together form a remarkable family, and they are grouped under the name halogens or salt-formers-aAs, sea- salt; yevvd.w, I produce. J. S. C. Schweigger used this term in 1811, and it was also \:\mployed by J. J. Berzelius 1 for the non-oxygenated negative radicles-simple or compound-which combine with the metals to form salts. J. J. Berzelius was inclined to 'restrict the term more particularly to the simple radicles F, CI, Br, I, and the compound radicle CN. J. J. Berzelius' term halogen has been retained for the four elements, and cyanogen dropped from the list. The binary salts-fluorides, chlorides, bromides, and iodides-are called halides, halide salts, or haloid salts. This term was also employed by J. J. Berzelius for the salts formed by the union of thc metals with fluorine, chlorine, bromine, iodine, and cyanogen; as before, cyanogen has again been dropped from the list. The first member of the family of halogens, fluorine, is the most chemically active element known; the chemical activity of the other members decreases with in- creasing at. wt. Fluorine can scarcely be said to occur free in nature, although C. A. Kenngott (181)3) and F. Wohler (1861) suggested that the violet felspar of Wolsendorf, and H. Becquerel and H. Moissan (18 0) 2 that the violet fluorspar from Quincie (Vil1efranche), probably contain free fluorine as an occluded gas. These varieties of fluorspar were designated hepatischer Flussspath and Btink- jlussspath by K. C. von Leonhard (1821) and J. F. L. Hausmann (1847).3 When these minerals are powdered they emit a peculiar odour recalling ozone, and this has been attributed by various observers to the presence of various substances .g. hypo- chlorous acid (M. Schafhautel), ozone (C. F. SchOnbein), free fluorine, or of fluorine from the dissociation of an unstable fluoride or perfluoride (0. Loew). 4 The chemical reactions of the gas, however, were found by H. Becquerel and H. Moissan to correspond with fluorine which must be present either as occluded free fluorine, or else as an unstable perfluoride. The evidence is not decisive though the former is the more probable explanation of the reactions. P. Lebeau 5 obtained similar indications of fluorine in emeralds obtained from the vicinity of Limoges. Combined fluorine is fairly widely distributed in rocks. According to F. W. Clarke,6 it is about half as abundant as chlorine, since he estimates that the terrestrial matter in the half-mile crtIst-land and sea-contains 0'2 per cent. of chlorine, and 0'1 per cent. of fluorine. F. W. Clarke places fluorine the 20th and chlorine the 12th in the list of elements arranged in the order of their estimated abundance in the half-mile crust of the earth. Small quantities of fluorine are commonly present in igneous rocks. J. H.. L. V ogt estimated that fluorine is the more abundant in the acidic rocks; chlorine, in the basic rocks. The most charac- teristic minerals containing fluorine are jluorspar, jluor, or jluQrite-calcium fluoride -andcryoUtl!-a double fluoride of aluminium and sodium; the less important or rarer fluoriferous minerals are: jluellite, AlFa.H20; chiolite, 5NaF.3AIF 3 ; sellaite, MgF2 ; tysonite, (Ce, La, Di)Fa ; pachnolite and thomsenolite, NaF.CaF 2.AlFa.HzO; ralstonite, 2NaF.MgF2.6AI(F,OH)g.4H 2 0; prosopite, CaF 2 .2Al(F,OH)a. Fluorine is als9 con- tained in some phosphates--e.g.,fluorapatite, phosphorite, sombrerite, coprolites, VOL, II. 1 B 2 INORGANIC AND THEORETICAL CHEMISTRY and staffelite; and in some silicates .g. topaz, tourmaline, herderite, yttrocerite, amphibole, nocerine, kodolite, melinophane, hieratite, lepidolite, and in many other silicate minerals. Several mineral waters have been reported to contain minute quantities of soluble fluorides. The spring at Gerez (Portugal) is one of the richest, for, according to C. Lepierre,7 it contains 0'296 to 0'310 grm. of soJid matter per litre, and of this, 0'022 to 0'027 grm. is an alkali fluoride; and of the 93 spring waters examined by P. Carles, 87 contained soluble fluorides. F. Parmentier has denied the existence of fluorine in many waters in which it is supposed to exist; but according to A. Gautier and P. Clausmann, all mineral waters contain fluorine, and the proportion is greatest in waters of volcanic origin. Thermal alkali bicarbonate waters are particularly rich in the element, although the proportion does not appear to depend upon the temp. As a general rule, mineral waters of the same kind show an in- crease of fluorine accompanying a rise in the total salts. In the case of calcium sulphate waters, whatever their origin, the amount of fluorine is about 2 mgnns. per litre. In 1849, G. Wilson reported on the occurrence of fluorine in the Clyde waters, and in the North Sea; and generally it has been found that sea water contains about three milligrammes per litre; the proportion varies slightly in different places and at different depths.. A. Gautier 8 found about 0'11 mgrm. of combined fluorine per litre of gas collected from a fumerole fissure in the crater of Vesuvius; and 3'72 mgrms. f Jer litre in the condensed water from the boric acid fumerole of a spring at Lardere 10 (Tuscany). At the beginning of the nineteenth century L. J. Proust and M. de la Metherie 9 first notiqed the presence of fluorine in bones, and the fact has since been confirmed by numerous others. A. Carnot found 0'20 to 0'65 per cent. of calcium fluoride in fresh bones, while old fossil bones contained much more-O.88 to 6'21 per cent. This fact was first noticed by J. Stocklasa in 1889. Modern bones were found by A. Car- not to contain a minimum proportion of fluorine; tertiary bones contained more; mesozoic bones stili more; and in silurian and devonian bones, the proportion of fluorine was nearly the same as in apatite. A. Carnot attributes the progressive enrichment of bones to the action of percolating waters containing a small proportion of fluorides in soln. .g. the waters of the Atlantic contain 0'822 grm. per cubic metre. According to F. Hoppe, the enamel of the teeth contains up to 2 per cent. of calcium fluoride; and according to W. Hempel and W. Scheffler, the teeth of horses contain 0'20 to 0'39 per cent. of fluorine, and the teeth of man, 0'33 to 0'59 per cent.1 0 - unsound teeth had but 0'19 per cent. of fluorine. P. Carles 11 found 0'012 per cent. of fluorine in the shells of oysters and mussels living in sea water, while fossil oyster shells contained 0'015 per cent. He also reported about one-fourth as much fluorine in fresh-water mussel shells as is present in the shells of sea-water mussels. The brain (E. N. Horsford),12 blood (G. Wilson, and G. O. Rees), and the milk of animals (F. S. Horstmar) have some fluorine. The brain of man contains about 3 mgrms. of fluorine, and although the lol? of fluorine in the animal and vegetable organism has not been clearly defined, some physiologists believe that the presence of fluorine is necessary, in some subtle way, to enable the animal organism to assimilate phosphorus. G. Tammann found that least fluorine was contained in the shells of eggs, and most in the yolks. About 0'1 per cent. of fluorine occurs in the ash of vegetable matter-particularly the grasses.1 3 A. G. Woodman and H. P. Talbot reported that fluorine is common in malt liquors; most malted beers contain not less than 0'2 mgrm. per litre. T. L. Phipson has reported 3'9 per cent. of fluorine, and 32.45 of phosphoric aeid in fossil wood from the Isle of Wight, thus showing that the wood had been "fossilized by phosphate of lime and fl uorspar." REFERENCES. 1 J. J. BerzeliuB, Lehrbuch der Ohemie, Dresden, 1. 266, 1843 ; J. S. C. Schweigger, Schweigger'8 Journ., 3. 249, 1811. THE HALOGENS 3 J C. A. Kenngott, Sitzber. Akad. Wien, 10. 296, 185: ; 11. 16, 1853; A. W. von Hofmann, J. 111m Liebig'a and F. Wohler' a Bri£jwechael in dem Jahren 1829-73, Braunschweig, 2. 107, 1888; H, Becquerel and H. Moissall, Oompt. Rend., 111. 669, 1890. · l{, C. von Leonhard, Harulbuch der Oryktog'IW8ie, Heidelberg, 565, 1821 ; J. F. L. HausmalU1, Ha7ll1huch der Mimralogie, Gottingen, 144], ] 847., · M. SchafhiiuteJ, Liebig'a Ann., 46. 344, 1843; C. F. Schonbeln, Journ. prakt. Ohem., (I), 74. 325, 1858; (I), 88. 95, 1861 ; G. Wyrouboff, BuU. Soc. Ohim., (2), 5. 334, 1866; G. Meissner, Untersuchungen wer den Saueratofj, Hannover, 1863; A. Schrot.ter, Sitzber. Akad. Wien, 41. 725,1860; Ohem. ?Jtg., 25. 355, 1901 ; J. Garnier, ib., 25. 89, 1901; T. Zettel, ib., 25. 385, 1901; H. Moissan, ib., 25. 480, 1901; O. Loew, Rer., 14. 1I44, 2441, 1881. I P. Lebeau, Oompt. Rend., 121. 601, 1895. · F. W. Clarke, The Data 0/ Geochemi8try, Wasllington, 34, 1916; J. H. L. Vogt, Zeit. prakt. Owl., 225, 314, 377, 413, I8!!8; 10, 1899. , C. Lepierre, Oompt. Rcnd., 128. 1289, 1899; P. Carles, ih., 144. 37,201,437, 1907; F. Par- mentier, ib., 128. lloo, 1899; A. Gautier and P. Clausmann, ib., 158. 1389,1631, 1914; G. Wilson, B. A. Rep., 47, 1849; Ohemi8t, 1. 53, 1850. · A. Gautier, Oampt. Rend., 157. 820, 1913 ; V. R. Mat!eucci, ib., 129. 65, ] 899; J. Stocklasa, C/tem. Ztg., 30. 740, 1906; A. Brun, Recherchea aur l'exhalaison volcanique, Geneve, 19I1. · J. L. Proust., JOUr'll. PhYR., 42.224,1806; M. de la Metherie, ib., 42.225,1806; A. Carnot, Camp!. Re7ll1., 114. 1189, 1892; 115. 246, 1892; J. Stocklasa, Biedermann'a Oen/rh., 18. 444, 1889. U F. Hoppe, Arch. path. Anat., 24. 13, 1862; W. Hempel and W. Scheffler, Zeit. anorg. Ohem., 20. 1, 1899 ; E. Wrampermeyer, Zeit. a1U1,I. Ohem., 32. 342, 1893; T. Gassmann, Zeit. phY8iol. Ohen!.,55. 455, 1908. )] P. Cadcs, Oompt. Rend., 144. 437, 1240, 1907. 12 E. N. Horsford, Liebig\ Ann., 149. 202, 1869; G. 0 Rees, Phil. Mag., (3), 15. 558, 1839; G. Tammallll, Zeit. phY8ioi. Ohem., 12. 322, 1888; Journ. Ph arm. OMm., (5), 18. 109, 1888; F .r. Nickles, Oampt. Rend., 43.885,1856; F. S. Horstmar, Pog!!. Ann., 111.339, 1860; G. Wilson,. B. A. Rep., 67, 1850; Edin. Phil. Journ., 49. 227, 1850; Proc. Roy. Soc. Ed.in., 3. 463, 1857. 13 H. Wilson, Journ. prakt. Ohem., (1),57.246,1852; H. Ost. Ber., 26.151,1895; F. J. Nickles, Ann. Ohim. PhY8., (3), 53. 433, 1858; T. L. Phipson, Ohem. New8, 66. 181, 1892; Oompt. Rend., 115.473,1892; A. G. Woodman and H. P. Talbot, Journ. Amer. Ohem. Soc., 20. 1362,1898. 2. The History of Fluorine The mineral now known as fluorspar or fluorite was mentioned in 1529 by G. Agricola, in his Bermannus, sive de re m.etallica dialog us (Basilire, 1529),and designated fluores , which, in a later work 1 by the same writer, was translated into Blmse. A. J. CronBtedt,2 in 1758, use'd the terms Fluss, Flusspat, and Glasspat, synonymously. C. A. Napione (1797) called the mineral flUQrite; F. S. Beudant (1832), fluorine.. and M. Sage (1777), spath fusible. These terms are derived from the Latin fluo, I flow, in reference to the fluxing action and the ready fusibility of the mineral; conseque'ntly, fluor lapis, spatum vitreum, and Glasspath mean the fluxing stone. J. G. Wallerius 3 refers to the luminescence of the mineral when warmed, and this phenomenon led to its being called lithophosphorus and phosphoric spar. The variety which gives a greenish phosphorescence is called chlorophane- X>Wpo , green; cpa{l'w, I appear-and also pyro-emerald. . H. Kopp reports 4 that H. Schwanhardt in 1670 etched glass by the action of fluorspar and sulphuric acid, and that in 1725, M. Pauli made a liquid for etching glass by mixing nitric acid and powdered fluors,par. In 1764, A. S. Marggraff 5 distilled the mixture of sulphuric acid and fluorspar in a glass retort, and found a white powder to be suspended in the water of the receiver. He therefore concluded that the sulphuric acid separates a volatile earth from the fluorspar. C. W. Scheele 6 repeated A. S. Marggraff's experiment, and, in his Examen chemicum fluoris mineralis fJ'usque acidi (1771), concluded that the sulphuric acid liberates a peculiar acid which is united with lime in fluorspar. The acid was called Flusssiiure-fluor acid-and fluorspar was designated flusssiiurer Kalk. After the expulsion of the fluor acid from the lime by sulphuric acid, selenite-calcium sulphate-remained in the retort. He found that hydrochloric, nitric, or phosphoric acid could also be used in place of sulphuric acid with analogous results. M. Boullanger 7 took the 4 INORGANIC AND THEORETICAL CHEMISTRY view that Scheele's fluor acid was nothing but muriatic acid combined with some earthy substance, and A. G. Monnet that it was a volatile compound of sulphuric acid and fluor. C. W. Scheele,8 however, refuted both hypotheses in 1780; and concluded: ' I hope that I have now demonstrated that the acid of fluor is and remains entirely a mineral acid 8ui generi8. C. W. Scheele generally used glass retorts for the preparatioR of the acid, and he was much perplexed by the deposit of silica obtained in the receiver. C. W. Scheele thought that the new acid had the property of forming silica when in contact with water, and it was therefore regarded as containing combined silica. The source of the silica was subsequently traced by J. C. F. Meyer and J. C. Wiegleb 9 to the glass of the retorts, and was not formed when the distillation was effected in metal vessels, and the acid Vl!.pours dissolved in water contained in leaden vessels. The gas obtained when the fluorspar is treated with sulphuric acid in metal vessels is hydro- fluoric acid, and if in glass vessels, some hydrofluosilicic acid is mixed with the hydrofluoric acid. In Lavoisier's system,lO Seheele's aeid of fluor became l'acide fluorique-a com- bination of oxygen with an unknown radiele,fluorium; and in 1789, A. L. Lavoisier wrote: It remains to-day to determine the nature of the fluoric radicle, but since the acid has not yet been decomposed, we cannot form any conception of the radicle. In 1809, J. L. Gay Lussac and L. J. Thenard 11 attempted to prepare pure hydro- fluoric acid, and although they did not succeed in making the anhydrous acid, they did elucidate the relation of silica and the silicates to this acid. H. Davy's work on the elementary nature of chlorine was published about this time; and he received two letters-dated Nov. 1st, 1810, and Aug. 25th, 1812 12-from A. Amphe sUggest-. ing " many ingenious and original arguments" in favour of the analogy between hydrocWoric and hydrofluoric acids. In the first letter, A. Ampere said: It remains to be seen whether electricity would not decompose liquid hydrofluoric acid if water were removed as far as possible, hydrogen going to one side and oxyfluoric acid to the other, just as when water and hydromuriatic acid are decomposed by the same agent. 'rhe only difficulty to be feare(i is the combination of the oxyfiuoric acid set free with the conductor with which it would be brought into contact in the nascent state. Perhaps there is no metal with which it would not combine, but supposing that oxyfluoric acid should, like oxymuriatic acid, be incapable of combining with carbon, this latter body might be a sufficiently good conductor for it to be used with success as such in this experi. ment. In the second letter, A. Ampere suggested that the supposed element be called le fluor-fluorine-in agreement with the then recently adopted name chlorine- Freneh, le chlore. A. Ampere's suggestion has been adopted universally. No one doubted the existence of the unknown element fluo.rine although it successfully resisted every attempt to bring i.t into the world of known facts. Belief in it existence rested on the many analogies of its compounds with the other three members of the halogen family. For over seventy years it was neither seen nor handled. During this time, many unsuccessful experiments were made to isolate the element. H. Davy 13 thus describes his attempts: I undertook the experiment of electrizing pure liquid fiuoric acid with considerable interest, as it seemed to offer the most probable method of ascertaining its real nature, but considerable difficulties occurred in executing the process. The liquid fiuoric acid im. mediately destroys glass and all animal and vegetable substances, it acts on all bodies containing metallic oxides, and I know of no substances which are not rapidly dissolved or decomposed by it, except metals, charcoal, phosphorus, sulphur, and certaiu combinations of chlorine. I attempted to make tubes of sulphur, of muriates of lead, and of copper containing metallic wires, by which it might be electrized, but without success. I succeeded, THE HALOGENS 5 however, in boring a piece of horn silver in such a manner that I WI!.'3 able to cement a platlna wire into it, by means of a spirit lamp, and by inverting this in a tray of platina filled with liquid fluoric aeid I contrived to submit the fluid to the agency of electricity in such a manner that in successive experiments it was possible to collect any ell!.'3tic fluid that might be produced. Having failed to isolate the element by the electrolysis of hydrofluoric acid and the fluorides, H. Davy tried if the element could be driven from its combination by double decomposition. He attempted to drive the" fluoric principle" from the dry fluates of mercury, silver, potassium, and sodium by means of cWorine. He said: The dry salts were Introduced in small quantities into gll!.'3s retorts, which were exhausted and then fllled with pure chlorine; the part of the retort in contact with the salt WI!.'3 heated gradually till it became red. There was soon a strong action, the fluate of mercury WI!.'3 rapidly converted into corrosive sublimate, and the fluate of silver more slowly became horn silver. In both experiments there was a violent action upon the whole of the interior of the retort. On examining the results, it was found that in both instances there had been a considerable absorption of chlorine, and a production of silicated fluoric acid gl!.'3 and oxygen gl!.'3. I tried similar experiments with similar results upon dry fluate of potassa and soda. By the action of a red-heat they were slowly converted into muriates with the absorption of chlorine, and the production of oxygen, and silicated fluoric acid gl!.'3, the retort being corroded even to its neck. ' H. Davy assumed that his failure to obtain the .unknown element was due to the potency of its reactions. H. Davy tried vessels of sulphur, carbon, gold, horn silver, and platinum, but none appeared to be capable of resisting its action, and" its strong affinities and high decomposing agencies" led to its being regarded as a kind of alcahest or universal solvent. G. Aime (1833) employed a vessel of caoutchouc, with no better result. The brothers C. J. and T. Knox (1836) 14 sagaciously tried to elude this difficulty by treating silver or mercury fluoride with cWorine in an appa- ratus made of fluorspar itself. E. Fremy believed that the failure in this as well as in P. Louyet's analogous attempt with fluorspar or cryolite vessels, in 1846, was due to the fact that the two fluorides do not decompose when moisture is rigorously excluded; and, if moisture be present, they form hydrofluoric acid. E. Fremy also did not succeed in decomposing calcium fluoride by means of oxygen, when heated to a high temp. in a platinum tube. E. Fremy electrolyzed fused fluorides -calcium, potassium, and other metal fluorides-in a platinum crucible with a platinum rod as anode. The platinum wire electrode was much corroded, and a gas was evolved which E. Fremy believed to be fluorine because it decomposed water forming hydrofluoric acid, and displaced iodine from iodides. He was able to decompose calcium fluoride at a high temp. by means of chlorine, and particularly when the fluoride is mixed with carbon. E. Fremy, however, mad no further progress in isolating the elusive element, althtlugh he did show how anhydrous hydrofluoric acid could be prepared. G. Gore 15 made some expe iments on the electrolysis of silver fluoride aud on the action ,of chlorine or bromine on silver fluoride at 15'5° for 38 days, and at 110° for 6 days, in vessels of various kinds-with vessels of carbon, a volatile carbon fluoride WI!.'3 formed. H. Kammerer 16 failed to prepare the gas by the action of iodine on silver fluoride in sealed glass tubes; according to L. Pfaundler, the product of the action is a mixture of silicon fluoride and oxygen. O. Loew heated cerium tetrafluoride, OeF,.H 2 0, or the double salt, 3KF.2CeF ..2H 2 0, and o1<>tained a gas, which he considered to be fluorine, when the tetra- fluoride decomposed forming the trifluoride, OeF a' B. Brauner also obtained a gas resem- bling chlorine by heating lead tetrafluoride, or double ammonium lead tetrafluoride, or potBBsium hydrogen lead fluoride, KaHPbF.. In the latter cl!.'3e a mixture of potBBsium fluoride, KF, and lead difluoride, PbF2' remained. O. Ruff claims to have made a little fluorine by heating the com pound HKPbF 8' As H. Moissan has said, it is possible that fluorine might be obtained by a chemical process in which a higher fluoride decomposes into a lower fluoride with the liberation of fluorine-say, 20eF.=20eF a +F 2 . 0.. Ruff has failed to confirm B. Brauner's observations with the fluorides in question. With lead tetrafluoride in a platinum vessel, lead difluoride and platinum tetrafluoride are formed; liq uid or gl!.'3eous silicon tetrafluoride is practically .without action on the salt although a small quantity of a gas which acts on potassium iodide is formed without altering the 6 INORGANIC AND THEORETICAL CHEMISTRY composition of the gas. Antimony pentafluoride acts similarly. With sulphur and iodine the corresponding hjgher fluorides are formed. Other suggestions have also been made to prepare fluorine by chemical processes--O. T. Christensen 17 proposed heating the higher double fluorides of manganese; A. C. Oudemans, potl!.'3sium fluochromate; and H. Moissan, platinum fluophosphates. About 1883. H. B. Dixon and H. B. Baker made an attempt to displace fluorine by oxygen from uranium pentafluoride, UFo. A. Baudrimont tried the action of boron trifluoride on lead oxide without succes . Abortive attempts have been made by L. Varenne, J. P. Prat, P. eillis, and T. L. Phipson ,. to prepare the gas by wet processes analogous to those employed for chlorine by the oxidation of soln. containing hydrofluoric acid. We now know that this is altogether a wrong line of attack. Some of the dry processes indicated above may have furnished some fluorine; for example, in H. B. Dixon and H. B. Baker's experiment, silver foil in the vicinity of the uranium fluoride was spotted with white silver fluoride; gold foil, with yellow auric fluoride; and platinum foil, with chocolate platinic fluoride. In 1834, M. Faraday 19 thought that he had obtained fluorine" in a separate state" by electrolyzing fused fluorides, but later, he added: I have not obtained fluorine; my expectations, amounting to conviction, passed away one by one when subject to rigorous examination. This was yirtually the position of the fluorine question about 1883, when H. Moissan,20 a pupil of E. Fremy, commenced systematic work on the subject, and the reports of the various stages of his work have been collected in his important monograph Le fluor et ses composes (Paris, 1900). He first tried (1) The decomposition of gaseous fluorides by sparking-e.g. the fluorides of silicon, SiF 4 ; phosphorus, PF 5 ; boron, BF 3 ; and arsenic, As]'3' The silicon and boron fluorides are stable. Phos- phorus trifluoride forms the pentafluoride. The fluorine derived from phosphorus pentafluoride reacts with the material of which the vessel is made; similarly with arsenic. fluoride. (2) The action of platinum at a red heat on the fluorides of pho.sphorus and silicon. Phosphorus pentafluoride furnishes some fluorine which unites with the platinum of the apparatus used; phosphorus trifluoride formed the pentafluoride and fluo-phosphides of platinum; silicon tetrafluoride gave no signs of free fluorine; H. Moissan came to the conclusion that no reaction carried out at a high temp. was likely to be fruitful. (3) The electrolysis of arsenic trifluoride to which some potassium hydrogen fluoride was added to make the liquid conducting; any fluoride given off at the anode was absorbed by the electrolyte forming arsenic pentafluoride. H. Moissan then tried the electrolysis of highly purified anhydrous hydrofluoric acid, but he found, consonant with G. Gore's and M. Faraday's observations,21 that anhydrous hydrofluoric acid is a non-conductor of electricity. If a small quantity of water be present, this alone is decomposed, and a large quantity of ozone is formed. As the water is broken up, the acid becomes less and less conducting, and, when the whole has disappeared, the anhydrous acid no longer allows a current to pass. He obtained an acid so free from water that "a current of 35 amperes furnished by fifty Bunsen cells was totally stopped." The current passed readily. when fragments of dry potassium hydrogen fluoride KF.HF, were dissolved in the acid, and a gaseous product was liberated at each electrode. Success! The element fluorine was isolated by Henri Moissan on June 26th, 1886, during the electrolysis of a soln. of potassium fluoride in anhydrous hydrofluoric acid, in an apparatus made wholly of platinum. In this way, H. "Moissan solved what H. E. Roscoe called one of the most difficult problems in modern chemistry. While the new element possessed special properties which gave it an individuality of its own, and a few surprises occurred during the study of some of its combinations; yet the harmonious analogy between the members of the halogen family-fluorine, chlorine, bromine, and iodine-was fully yjndicated. With fluorine in the world of reality, chemists were unanimous in placing the newly discovered element at the head of the halogen family, and in that very position which had been so long assigned to it by presentiment or faith. THE HALOGENS 7 REFERE cEs. 1 G. Agricola, lnterpretatio Germanica vocum rei metallica!, Basil, 464, 1546. · A. J. Cronstedt, Mine:ralogie, Stockholm, 93, 1758; C. A. Napione, Elementi di Minercilogia, Turin, 373, 1797; F. S. Beudant, Truite elementaire de mineralogie, Paris, 2. 517, 1832; M. Sage, Elemens de mineralogie docimasti'lue, Parig, 155, 1777. 3 J. G. Wallerius, Mineralogie, Berlin, 87, 1750. · H. Kopp, Geschichte der Ohemie, Braunschweig, 3. 368, 1845. · A. S. Marggraff, M em. Acad. Berlin, 3, 1768. · C. W. Scheele, Mem. A cad. Stockholm, (I), 33. 120, 1771; Opuscula chemica et physica, Lipsre, 2. I, 1789. 7 M. Boullanger, Experiences et obse:rmtions sur Ie spath vitreux, 01£ fluor spathique, Paris, 1773 ; A. G. Monnet, Rozier's observation9 sur la physique, 10. 106, 1777; Ann. Ohim. Phys., (I), 10. 42, 1791. 8 C. W. Scheele, Mem. Acad. Stockholm, (2), 1. I, 1780; Opuscula chemica et physica, Lipsae, 2.92,1789; Ohemical Essays, London, I-51, 1901. 9 J. C. F. Meyer, Schr. Berlin. Ge8. NaturJors., 2.319,1781; J. C. Wiegleb, Orell's Die neuesten Entdeclcungen in der Ohemie, 1. 3, 1781; C. F. Bucholz, lb., 3. 50, 1781; L. B. ,G. de Morveau, Journ. Phys., 17. 216, 1781 ; M. H. Klaproth, Orell's Ann., 5. 397, 1784; F. C. Achard, ib., 6. 14(;, 1785; M. Puymaurin, ib., 3. 467, 1783. 10 A. L. Lavoisier, Traite el&mentaire de chimie, Paris, 1. 263, 1789. 11 J. L. Gay Lussac and L. J. Thenard, Ann. Ohim. Phys., (I), 69. 204, 1809. 12 A. Ampere, reprinted Ann. Ohim. Phys., (6), 4.8,1885; F. D. Chattaway, Ohem. News, 107. 25,37, 1913. 13 H. Davy, Phil. Trans., 103. 263, 1813 ; 104. 62, 1814; Ann. OMm. PhY8., (I), 88.271, 1813. 18 G. Aime, Ann. Ohim. Phys., (2), 55. 443, 1834; C. J. and T. Knox, Proc. Roy. Irish Acad.,1. 54,1841; Phil. Mag., (3), 9.107,1836; C. J. Knox, ib., (3),16. 199,1840; P. Louyet, Oompt. Rend., 23.960,1846; 24.434, 1847; E. Frerny, ib., 38.393, 1854; Ann. Ohim. PhY8., (3), 47. 5, 1856. IIi G. Gore, Phil. Trans., 160. 227, 1870; 161. 321, 1871; Ohem. News, 50. 150, 1884. 18 H. Kammerer, Journ. prakt. Ohem., (1),85.452,1862; (I), 90. 191,1863; A. Baudrimont, ill., (I), 7. 447, 1836; L. Pfaundler, Sitzber. Akad. Wien, 46. 258, 1863; O. Loew, Ber., 14. 1144, 2441, 1881; B. Brauner, ib., 14. 1944, 1881; Journ. Ohem. Soc., 65. 393, 1894; Zeit. anorg. Ohem., 98. 38, 1916; O. Ruff, ib., 98. 27, 1916; Zeit. angew. Ohem., 20. 1217, 1907. 17 O. T. Christensen, Journ. pruld. Ohern., (2), 34. 41, 1886; A. Baudrimont, ib., (1), 7. 447, 1836; A. C. Oudema,ns, Rec. Trav. Ohim. Pays-Ba8, 5. Ill, 1886; H. Moissan, Bull. Soc. Ohim., (3),5.454.1891; H. B. Dixon and H. B. Baker, Private communication. U T. L. Phipson, Ohem. New8, 4. 215, 1861; J. P. Prat, Oompt. Rend., 65. 345, 5ll, 1867 ; L. Varenne, ib., 91. 989, 1880; P. CiIIis, Zeit. Chern., 11. 660, 1868; G. Gore, Ohern. News, 52. 15, 1885; E Wedekind, Be:r., 35. 2267, 1902. 19 M. Faraday, Phil. Trans., 134. 77, 1834; Expe:rimental Researches in Electricity, London 1. 227, 1849. '" H. Moissan, Oompt. Rend.. 99. 655, 874, 1884; 100. 272, 1348, .1885; 101. 1490, 1885; 102. 763, 1245, 1543, 1886; 103. 202, 256, 850, 1257, 1886; 109. 637, 862, 1889; 128. 1543, 1899; Ann. Ohim. PhY8., (6), 12. 472, 1887; (6), 24. 224, 1891; Bull. Soc. Ohim., (3), 5. 880, 1891.: Les classiques de la 8c.ience, 7, 1914. 21 G. Gore, Phil. Trans., 159. 189. 1869; M. Faraday, ib., 124. 77, 1834. 3. The Preparation of Fluorine When an electric current is passed through a cone. aq. soln. of hydrogen chloride, chlorinE; is liberated at the anode, and h:ydrogen at the cathode. When aq. hydro- fluoric acid is treated in the same way, water alone is decomposed, for oxygen is libelated at the anode, and hydrogen at the cathode. The anhydrous acid does not conduct electricity, and it cannot therefore be electrolyzed. H. Moissan found that if potassium fluoride be dissolved in the liquid hydrogen fluoride, the Boln. readily conducts electricity, and when electrolyzed, hydrogen is evolved at the cathode, and fluorine at the anode. In the first approximation, it is supposed that the primary products of the electrolysis are potassium at the anode, fluorine at the cathode: 2KHF 2=2HF +2K+F 2' The potassium reacts with the hydrogen fluoride reforming fluoride and liberating hydrogen: 2K+2HF=2KF+H2' The reaction is pmbably more complex than this, and the platinum of the electrodes plays a part in the secondary reactions. Possibly the fluorine first forms platinum fluoride, PtF4' which produces a double compound with the potassium fluoride. 8 INORGANIC AND 'J'HEORE'l'ICAL CHEMISTRY This compound is considered to be the electrolyte which on decomposition forms the two gases and a double potassium platinum fluoride which is deposited as a black mud. This hypothesis has been devised to explain why the initial stage of the electrolysis is irregular and jerky, and only after the lapse of an hour, when the substances in soln. are in sufficient quantities to make the passage of the current regular, is the evolution of fluorine regular. O. Ruff 1 has shown that ammonium fluoride can be used in place of the potassium salt. H. Moissan flrst conducted the electrolysis In a u-tube made from an alloy of platinum and iridium which is less attacked by fluorine than pJatinum alone. Later experiments E FIG. L-Tube for the Electro- lysis of Hydrofluoric Acid. FIG. 2.-Moissan's Process for Fluorine. showed that a tube of copper could be employed. The copper is attacked by the fluorine, forming a surface crust of copper fluoride which protects the tube from further action. Electrodes of platinum iridium alloy were used at first, but later electrodes of pure platinum were used, even though they were rather more attacked than the alloy with 10 per cent. of iridium. The electrodes were club-shaped at one end so that they need not be renewed so often. The positive electrode was often completely corroded during an experiment, but the u-tube scarcely suffered at all. A copper tube is illustrated in Fig. 1. The open ends of the tube are closed with fluorspar stoppers ground to fit the tubes and bored with holes which grip the electrodes. The joints are made air-tight with lead washers and shellac. The u-tube, during the electrolysis, is F gd$..... surrounded with a glass cylinder, B, into which liquid methyl chloride Is passed from a steel cylinder via the tube A, Fig. 2. Liquid methyl chloride boils at _23°, and it escapes through an exit tube. The fluorine is passed through a spiral platinum tube also placed In a bath of evaporating liquid methyl chloride, C. This cools the spiral tuhe down to about _50°, and condenses any gaseous hydrogen fluoride, which might escape with the fluorine from the u-tube. The electrolysis was carried out at a low temp. in order to prevent the gaseous product being diI. with the vapour of hydrogen fluoride, arid also to diminish the destruc- tive action of the fluorine on the apparatus. In his later work, H. Molssan cooled the u-tube used for the electrolysis by using a bath of aCetone with solid carbon dioxide in suspension. This cooled the appara- FIG. 3.-Fluorine by the Electrolysis tus down to about - 80°. The temp. of the electrolysis of Fused Alkali Hydrofluoride. vessel should not be so low that the potassium hydrogen fluoride crystallizes out. Hence, O. Ruff and P. Ipsen 2 preferred to cool the electrolysis vessel with a freezing mixture of calcium chloride, and condensed the hydrogen fluoride vapours in a copper condenser C, Fig. 2, cooled with liquid air. The fluorine which leaves the condenser C, travels through two small platinum tubes, D and E. containing lumps of sodium fluoride, which rerrlove the least traces of hydrogen fluoride by forming NaF.HF. A glass cylinder is placed outside each of the two cylinders containing methyl chloride. The outer cylinders contain a few lumps of calcium chloride, so as to dry the air in the vicinity of the cold jacket, and prevent the THE HALOGENS 9 deposition of frost on the cylinders. With a current from 26 to 28 B en ells in s es, and an apparatus containing from 90 to 100 grms. of anhydrous hydrofluOric aOld contalmng in soln. 20 to 25 grrns. of potassium hydrogen fluoride, H. Moissan obtained between two and three litres of fluorine per hour. C.Poulenc and M. Meslans 3 have devised a copper apparatus for the preparation of fluorine on a large scale; and likewise a portable laboratory apparatus, also of copper. They substitute a perforated copper diaphragm in place of the U-tube for keeping the two electrode products separate. The platinum anode is hollow, and is cooled internally. G. Gallo did not get good results ith this apparatus.. W. L. Argo a.nd co-workers ]?repared fluorine by the electr lysls of molten potassmm hydrofluor de in an electrically heated copper vessel whlCh served as cathode, the anode bemg made of graphite. A copper diaphragm with slots was used as illustrated in Fig. 3. The bubbles of hydrogen evolved during the electrolysis were deflected from the interior of the diaphragm by means of a false bottom. The graphite anode was connected with a copper terminal and insulated by a packing of powdered fluorspar -current, 10 amps., 15 volts; temp., 240°-250°; efficiency, 70 per cent. These co-workers also recommend sodium hydrofluoride because it is non-deliquescent; decomposes below the fusion temp.; contains more available fluorine for a given weight; and is less expensive. REF]1RENCES. 1 O. Ruff, Zeit. angew. Ohern., 20. 1217, 1907; O. Ruff and E. Geisel, Ber., 36.2677, 1903. S O. Ruff and P. Ipsen, Bel'., 36. 1177, 1904. a C. Poulenc and M. Meslans, Ret'. Gen. Acetylene, 230, 1900; G. Gallo, Atti Accad. Lincei, (5),19. i, 206, 1910; W. L. Argo, F. C. Mathers, R. Hamiston, and C. O.Anderson. JO'Um. Phy8. CMm., 23.348,1919; Ohern. En]., 'lfl. 107,1919; Trans. A mer. Electrochem. Soc., 35. 335, 1919. 4. The Properties of Fluorine Is fluorine an element 1 Since fluorine had never been previously isolated, it remained for H. Moissan to prove that the gas he found to be liberated at the positive pole is really fluorine. Many of its physical and chemical properties, as will be shown later, agree \vith those suggested by the analogy of the fluorides with the chlorides, bromide, and iodides. It was found impossible to account for its properties by assuming it to be some other gas mixed with nitric acid, chlorine, or ozone; or that it is a hydrogen fluoride richer in fluorine thari the normal hydrogen fluoride. To show the absence of hydrogen, H. Moissan allowed the gas to pass directly from the positive pole through a tube containing red,hot iron; any hydrogen so formed was collected in an atm. of carbon dioxide. The latter was removed by absorption in potassium hydroxide. In several experiments a small bubble of gas was obtained whioh WIlB air, not hydrogen. The increase in weight of the tube containing the iron corresponded exactly with the fluorine eq. of the hydrogen collected at the negative pole. The vapours of hydrogen fluoride were retained by a tube fllled with dry potassium fluoride. For example: In one experiment a platinum tube containing iron increased in weight 0'138 grm. while 80'01 c.c. of hydrogen were collected at the negative electrode. This represents 0'00712 grm. of hydrogen, and 0'00712 X 19=0'134 grm. of fluorine. This number is virtually the same as the weight of fluorine actually weighed. Fluorine at ordinary temp. is a greenish-yellow gas when viewed in layers a metre thick; the colour is paler and more yellow than that of chlorine. The liquid gas is canary-yellow; the solid is pale yellow or white. Moissan's gas has an in- tensely irritating smell said to recall the odour of hypochlorous acid or of nitrogen peroxide. Even a small trace of gas in the atm. acts quickly on the eyes and th mucous membranes; and, in contact with 'the skin, it causes severe burns, and rapidly destroys the tissues. If but a slight amount is present, its smell is not 10 INORGANIC AND THEORETICAL CHEMISTRY unpleasant. The relative density 1 of the gas (air unity) determined by H. Moissan in 1889, by means- of a platinum flask, was 1'26; that calculated for a diatomic gas of at. wt. 19'5 is 1'314, and B. Brauner attributed the difference to the presence of some atomic fluorine. H. Moissan's later results (1904) rendered B. Brauner's hypothesis unnecessary since a density of 1'31 was obtained. The gas employed previously is supposed to have been contaminated with a little hydrogen fluoride. Most of the physical properties of fluorine at a low temp. have been determined by H. Moissan himself and in conjunction with J. Dewar. 2 The sp. gr. of liquid fluorine is 1.14 at -200°, and 1'108 at its b.p. -187°. The sp. vol. of the liquid is 0'9025; and the mol. vol. 34'30. The capillary constant of the liquid is about one-sixth of that of liquid oxygen, and seven-tenths of that of water. The coefficient of ex- pansion 3 of the gas is 0'000304. The volume of the liquid changes one-fourteenth in cooling from -187° to -210°. When the gas is cooled by rapidly boiling liquid air, it condenses to a clear yellow liquid which has the boiling point -187° at 760 mm. press.; and the liquid forms a pale yellow solid when cooled by liquid hydrogen. The solid has the melting point -233°. The solid loses its yellow tint and becomes white when cooled down to -252°. Chlorine, bromine, sulphur, etc., likewise lose their colour at low temp. J. II. Gladstone's! estimate for the atomic refraction of fluorine for the D-line is 0'53; for the A-line 0'63 j and for the H-lineO'35 with the ,u-formula, and 0'92 and 0'84 respectively with the ,u2-formula. F. Swarts estimated 0'94 Ha, 1'015 D, and 0'963 H'Y with the ,u2-formula for fluorine in sat. organic compounds; and for unsaturated compounds with the ethylene linkage, Ha, 0'588; D, 0'665; H'Y,0'638. The atomic dispersion is 0'022 with sat. and 0'05 with the unsaturated compounds. J. H. Gl""dstone also made several estimates of the index of refraction of fluorine, and his 1870 estimate gave 1'4 (chlorine 9'9); in 1885 he placed it at 1'6; and in 1891, he considered it to be " extremely small, in fact, less than 1'0." The difficulty is due to the fact that when the magnitude of a small constant is estimated by subtraction from two large numbers the probability of error is large. A direct determination by C. Cuthbertson and E. B. R.. Prideaux gave for the index of refraction of fluorine for sodium light, ,u=1'000195, which makes the refractivity (,u-1) X 10 6 to be 195. The emission spectrum of fluorine has been investigated by H. Moissan and G. Salet. 5 The last named, in 1873, compared the spectra of silicon chloride and fluoride, and inferred that five lines in the spectrum of silicon fluoride must be attributed to the fluorine. H. Moissan's measurements, in 1889, measured 13 lines in the red part of the spectrum. The lines of wave-length 677,640'5,634, and 623 are strong; the lines 714, 704, 691, 687'5, 685'5, 683'5 are faint; and 749, 740, and 734 are very faint. Liquid fluorine has no absorption spectrum when in layers 1 cm. thick. According to P. Pascal,6 fluorine is diamagnetic; the specific magneticsuscepti- bility is -3'447 X 10- 7 ; and the atomic susceptibility calculated from the additive law of mixtures for organic compounds is -63XlO- 1 . Ionic fluorine is univalent and negative. The decomposition voltage required to separate this element from its compounds is 1'75 volts. 7 The ionic velocity (transport number) s of fluorine ions at 18° is 46'6, and 52'5 at 25° with a temp. coeff. of 0'0238. Fluorine possesses special characters which place it at the head of the halogen family. It forms certain combinations and enters into some reactions in a way which would not be expected if the properties of the element were predicted solely by analogy with the other members of the halogen family. From this point of view, said H. Moissan, l'etude des composes jluorPs reserve encore bien des surprises. Fluorine is the most chemically active element known. It combines additively with most of the elements, and it usually behaves like a univalent element although it is very prone to form double or complex compounds in which it probably exerts a higher valency. It also acts as an oxidizing agent. In the electrolysis of manganese and chromium salts a higher yield of chromic acid or manganic acid is obtained in the presence of hydrofluoric acid than in the presence of sulphuric acirl. 9 Fluorine THE HALOGENS 11 unites explosively with hydrogen in the dark with the production of a flame with a red border, and H. Moissan showed this by inverting a jar of hydrogen over' the fluorine delivery tube of his apparatus. The product of the a.ction is hydrogen fluoride which rapidly attacks the glass vessel when moisture is present, but not if the two gases are dry. Fluorine retains its great avidity for hydrogen even at temp. as low as '-252'5° when the fluorine is solid, and the hydrogen is liquid. H. Moissan and J. Dewar'lO broke a tube of solid fluorine in liquid hydrogen. A violent explosion occurred which shattered to powder the glass apparatus in which the experiment was performed. It is rather unusual for the chemical activity of an element to persist at such a low temp. The affinity of fluorine for hydrogen is so great that it vigorously attacks organic substances, particularly those rich in hydrogen. . The reaction is usually accompanied by the evolution of heat and light, and the total destruction of the compound. The products of the reaction are hydrogen fluoride, carbon, and carbon fluorides. The avidity of fluorine for hydrogen persists at very low temp., for turpentine and anthracene may explode in contact with fluorine at -210°. Even water is vigorously attacked by fluorine. If a small quantity of water is introduced into a tube containing fluorine, it is decomposed, forming hydrogen fluoride and ozone; the latter imparts an indigo-blue tinge to the gases in the jar. By measuring the volume of oxygen liberated when fluorine reacts with water, and measuring the exact quantity of hydrofluoric acid formed, H. Moissan showed that equal volumes of hydrogen and fluorine form hydrogen fluoride. If the reaction between fluorine and water be symbolized, H 2 0+F 2 =2HF +0, it follows that for every volume of hydrogen collected at the negative pole, half a volume of oxygen should be obtained. In one experiment H. Moissan collected 26'10 C.c. of oxygen, 52'SO C.c. of hydrogen. In another experiment he obtained 6'4 C.c. of oxygen per 12'5 C.c. of hydrogen and eq. of 24'9 c.c. of hydrogen fluoride. Liquid fluorine does not react with water. At -200°, liquid fluorine can be volatilized from the surface of ice without reaction. Neither oxygen nor ozone appears to react with fluorinEJ',and no oxygen compound of fluorine has yet been prepared. According to H. Moissau,l1 an unstable inter- mediate compound of ozone and fluorine is possibly formed when water acts on fluorine to form ozonized oxygen because the ozone smell does not appear until some time after the fluorine has been passed into the water. O. Ruff and J. Zedner have tried the effect of heating oxygen and fluorine in the electric arc, but obtained no signs of the formation of a compound of fluorine with oxygen or ozone, for when the gaseous product is passed over calcium chloride (which fixes the fluorine) a mixture is obtained quite free from fluorine. G. Gallo obtained signs of a very IllliItable compound of Ozone and fluorine which is explosive at -23°. Liquid oxygen dissolves fluorine, and if the temp. rises gradually, the first fraction which volatilizes is almost pure oxygen; the last fraction contains most of the fluoriue. If liquid air, which has stood by itself for some time, be treated with fluorine, a precipitate is formed which is very liable to explode. H. Moissan thinks it is probably fluorine hydrate. 12 Solid sulphur, seleniuni, and tellurium inflame in fluorine gas at ordinary temp. ; sulphur burns to the hexafluoride, SF 6' The reactivity of sulphur or selenium with fluorine persists at -187°, but tellurium is without action at this temp. Hydrogen sulphide and sulphur dioxide also burn in the gas-the former produces hydrogen fluoride and sulphur fluoride. Each bubble of sulphur dioxide led into a jar of fluorine produces an explosion and thionyl fluoride, SOF 2 , is formed; but if the fluorine be led into the sulphur dioxide, there is no action until the sulphur dioxide has reached a certain partial pressure when all explodes. If the fluorine be led into an atm. of sulphur dioxide at the temp. of the reaction, sulphuryl fluoride, S02F2' is formed quietly without violence. Sulphuric acid is scarcely affected by fluorine. Fluorine does not unite with chlorine at ordinary temp. O. Ruff and J. Zedner also obtained no result by heating fluorine and chlorine at the temp. of the electric 12 INORGANIC AND THEORETICAL CHEMISTRY arc. Liquid chlorine dissolv8s fluorine, but the dissolved gas escapes as the chlorine freezes. It is inferred that the gases do not react at the low temp. -80° when fluorine is dissolved iuliquid chlorine because (i) the gases evolved when the soln. is fraction- ally distilled showed no signs of an abrupt change in composition between 97'32 per cent. of fluorine at the beginning and 0'63 per cent. at the end of the operation; (ii) on cooling a soln. of fluorine in liquid chlorine, there is a tumultuous evolution of gas when the mixture freezes-the solid is chlorine, the gas fluorine. Bromine unites with fluorine at ordinary temp. with a luminous flame forming bromine trifluoride, BrFs. Similar remarks apply to iodine, where the pentafluoride, IF 5' is formed. The heat of the former reaction is small, the latter great. Liquid fluorine, however, does not react with or dissolve bromine or iodine at -187°, nor does it liberate iodine from potassium iodide. In the presence of water, chlorine reacts with fluorine forming hypochlorous acid; and bromine, hypobromous acid; some chloric or bromic acid may also be formed, and part of the water is also decom- posed by the excess of fluorine. If fluorine be passed into a 50 per cent. soln. of hydrofl.uoric acid, there is an energetic reaction accompanied by a flame in the midst of the liquid. The reaction of fluorine with gaseous or aq. soln. of hydrogen chloride, bromide, or iodide, is accompanied by flame. Most of the haloids of the metalloids are attacked with great energy by fluorine at ordinary temp. Fluorine does not unite with argon even if a mixture of the two gases be heated or sparked. Neither nitrogen or nitrous oxide, NzO, nor nitrogen peroxide, N0 2 , is attacked by fluorine at ordinary temp. 0. Ruff and J. Zedner also found no reaction occurred at the temp. of the electric arc between fluorine and nitrogen. Even at a dull red heat nitrous oxide remains unattacked by fluorine, but by sparking a mixture of fluorine and nitrous oxide, a mixture of nitrous oxide, nitrogen, and oxygen is formed, but no nitrogen oxyfluoride. 1s A little nitric oxide, NO, unites with fluorine at ordinary temp.; the reaction is attended by a pale yellow flame, and a volatile oxyfluoride is formed; but if the nitric oxide be in large excess, it is simply broken down into nitrogen and oxygen, and the excess of nitric oxide forms nitrogen peroxide. Ac.cording to H. Moissan and P. Lebeau, if the fluorine be in excess, at the temp. of liquid oxygen, a white solid is formed which, as the temp. rises, changes into a colou.rless liquid, boiling above 80°, and which furnishes on fractionation nitroxyl or nitryl fluorid , N0 2 F. F]uorine decomposes ammonia with inflammation; and a mixture of the two gases explodes. Phosphorus inflames in fluorine gas forming the pentafluoride, PF 5, if the fluorine be in excess; and the trifluoride, PFs, if the phosphorus be in excess. Arsenic forms the trifluoride, AsFs, with inflammation. Similarly with antimony; but bismuth is only superficially attacked. Both phosphorus and arsenic react with incandescence with liquid fluorine, but antimony remains unaltered. Phosphorus pent oxide, P 2 0 5 , is decomposed at a red heat forming the fluoride and oxyfluoride ; phosphorus tri- and penta-chloride are attacked with the production of flame; neither phosphorus pentafl.uoride nor phosphorus oxyfl.uoride is attacked. Arsenic trioxide and arsenic trichloride are attacked. Arsenic trifluoride, AsFs, absorbs fluorine, and the heat generated during the absorption led H. Moissan to suggest that some unstable arsenic penta fluoride is formed. Both boron and silicon unite with fluorine gas energetically and with incandes- cence, forming in the one case boron trifluoride, BFs, and in the other, silicon tetra- fluoride, SiF 4 , Boric oxide and silica react energetically in the cold. Boron trichloride, BCI s , at ordinary temp., and silicon tetrachloride, SiCLt, above 40°, both react with fluorine. Dry fluorine does not attack glass, for H. Moissan kept dry fluorine in glass vessels for two hours at 100°, without appreciable attack. Hydrogen fluoride behaves similarly. The slightest trace of moisture is sufficient to activate either gas. Dry lampblack becomes incandescent in fluorine; wood charcoal fires spontaneously; the vigour of the reaction is reduced at low temp., for boron, silicon, and carbon are not attacked by liquid fluorine. If powdered charcoal or soot be allowed to fall into a vessel containing liquid fluorine, the particles THE HALOGENS 13 become incandescent as they drop through the vapour, but the glow is quenched when the particles reach the liquid. The denser forms of carbon req uire a temp. of 50° to 100° before they become incandescent; retort carbon requires a red heat; and the diamond is not affected at that temp. Soft charcoal is quickly ignited in contact with the gas. The product of the reaction is usually a mixture of different carbon fluorides, but if the temp. of the reaction be kept low, carbon tetrafluoride alone is formed. H. Moissan 14 also found that fluorine acts on calcium carbide at ordinary temp. giving calcium fluoride and carbon tetrafluoride. Carbon monoxide and dioxide are not attacked in the cold; carbon disulphide. CS z , inflames forming carbon and sulphur fluorides; carbon tetrachloride, CC1 4 , reacts at temp. exceeding 30° forming chlorine and carbon tetrafluoride; cyanogen is decomposed at ordinary temp. with .the production of a white flame. According to W. L. Argo and co- workers, the unlighted gas issuing from a Bunsen's burner is immediately ignited by fluorine. According to B. Humiston, acetone in an open vessel takes fire; chloroform forms chlorine, phosgene, and carbon fluorides. With phosgene, a compound which appears to be carbonyl fluoride, COF z , was formed. The action of fluorine on ethYlene tetrachloride, C z C1 4 , is symbolized: C z C4+2Fz=C z F4+2Cl z , followed by Clz+CzC =CzC16' and C Z F 4 =CF 4 +C. The metals are in general attacked by fluorine at ordinary temp.; many of them become coated with a layer of fluoride which protects them from further action. These remarks apply to the metals: aluminium, bismuth, chromium, copper, gold, iridium, iron, manganese, palladium, platinum, ruthenium, silver, tin, zinc. The, formation of a protective skin of fluoride renders it possible to prepare fluorine in copper and platinum vessels at ordinary temp. Lead is slowly converted into the white fluoride at ordinary temp. If the temp. be raised, nearly all the metals are vigorously attacked with incandescence-for example; with tin and zinc, the ignition te p. is about 100°, and iron and silver, at bout 500°. Gold and platinum are slowly converted into their fluorides at about 500° or 600°. The metals of the alkalies and alkaline earths, thallium, and magnesium are converted with incandes- cence into their fluorides. Many of the metals which. in bulk are only attacked slowly, are rapidly converted into fluorides if they are in a finely divided condition. Thus fluorine forms a volatile fluoride with powdered molybdenum in the cold, but a lump of the metal is not attacked; tungsten is attacked at ordinary temp., and also forms a volatile fluoride-; electrolytic uranium, in fine powder, is vigorously attacked and burns, forming a green volatile hexafluoride. If niobium (columbium) or tantalum be warmed, the pentafluorides are formed. Liquid fluorine has nO action on many of the metals-e.g. iron. If mercury be quite still, a protecting layer of fluoride is formed, but if the metal be agitated with the gas, it is rapidly converted into the fluoride. The chlorides, bromides, iodides, and cyanides are generally vigorously attacked by fluorine in the cold; sulphides, nitrides, and phosphides are attacked in the cold or may be when warmed a little; the oxides of the alkalies and alkaline earths are vigorously attacked with incandescence; the other oxides usually require to be warmed. The sulphates usually require warming; the nitrates generally resist attack even when warmed. The phosphates are more easily attacked than the sulphates. The carbonates of sodium, lithium, calcium, and lead are decomposed at ordinary temp. with incandescence, but potassium carbonate is not decomposed even at a dull red heat. Fluorine does not act on sodium borate. Most of these reactions have been qualitatively'studied by H. Moissan,15 and described in his monograph, Le fluor et ses composes (Paris, 1900). Atomic and molecular weight of fl.uorine.-The combining weight of fluorine has been established by converting calcium fluoride,. potassium fluoride, sodium fluoride, etc., into the corresponding sulphates. In illustration, J. B.. A. Dumas (1860) found that one gram of pure potassium fluoride furnishes 1'4991 gram of potassium sulphate. Given the combining weights of potassium 39'1, sulphur 32'07, oxygen 16, it follows that if x denotes the combining weight of fluorine with 14 INORGANIC AND THEORETICAL CHEMISTRY 39'1 grams of potassium, 1: 1'4991=2KF: K 2 S0 4 =2(39'I+x): 174'27; or, x=19. H. Davy 16 made the first attempt in this direction in 1814 by converting fluorspar into the corresponding sulphate. His result corresponds with an at. wt. 18'81. J. J. Berzelius (1826) also employed a similar process and obtained first the value 19'16 and later 18'85. P. Louyet, in 1849, employed the same process, taking care that the particles of fluorspar did not escape the action of the sulphuric acid by the formation of a protective coating of sulphate. P. Louyet obtained 18'99 with nati ve fluorspar, and 19'03 with an artificial calcium fluoride. In 1860, J. B. A. Dumas obtained the value 18'95 with calcium fluoride; S. de Luca (1860), 18'97 ; H. Moissan (1890),19'011. P. Louyet, J. B. A. Dumas, and H. Moissan also converted sodium fluoride into sodium sulphate and obtained ,respectively the values 19'06, 19'08, and 19'07. P. Louyet and H. Moissan in addition converted barium fluoride into the sulphate and obtained respectively 19'01 and 19'02; and P. Louyet's value, 19'14, was obtained with lead fluoride. O. T. Christensen (1886) treated ammonium manganese fluoride, (N )2MnF 5, with a mixture of potassium iodide and hydro- chloric acid-one mol. of the salt gives a gram-atom of iodine. The liberated iodine was titrated with sodium thiosulph,atc. The value 19'038 was obtained. J. Meyer (1903) converted calcium oxide into fluoride and obtained 19'035. D. J. McAdam and E. F. Smith (1912) obtained 19'015 by transforming sodium fluoride into the chloride. E. F. Smit,h and W. K. van Haagen obt,ained 19'005 by converting anhydrous borax into sodium fluoride. E. Moles and 'IT. Batuecas estimated the at. wt. of fluorine from the density of methyl fluoride, and found 18'998:t 0'005 when the at. wt. of car00n is 12'000, and of hydrogen, 1'0077. The best determinations range between 18'97 and 19'14, and the best representative value of the combining weight of fluorine is taken to be 19. No known volatile com- pound of fluorine contains less than 19 parts of fluorine per molecule, and accordingly this same number is taken to represent the at. wt. The vapour density of fluorine, determined by H. Moissan, is 1'31 (air=I), that is, 28'755 Xl'31=37'7(H2=2). The molecule of fluorine is therefore represented by F 2 . Fluorine is assumed to be univalent since it forms fluorides like KF, NaF, tc. with univalent elements and radicles; CaF2' BaF 2 , etc" with bivalent radicles, etc. As indicated in connection with hydrogen fluoride, etc., there is, however, the great probability that fluorine also exhibits a higher valency in the more complex com- pounds like KF.HF, AlF3.3NaF, etc. 17 This also agrees withJ. Thomsen's observa- tions on the heat of the reaction between the acid and silica. REFERENCES. 1 H M:oissan, Campt. Rend., 109. 861, 1889; 138. 728, 1904; B. Brauner, Zeit. anorr}. Chern., 7. I, 1894; J. Sperber, ib., 14. 164, 374, 1897. 2 H. Moissan and J. Dewar, Campt. Rend., 124. 1202, 1897; 125. 505, 1897; 136. 785, 1903. 8 J. Sperber, Zeit. anarg. Chem" 14. 164, 1897. . 4 J. H. Gladstone, Phil. Trans., 160. 26, 1870; Amer. Jaurn. Science, (3), 29. 57, 1885; G. Gladstone, Phil. Mag., (5), 20. 483, 1885; J. H. and G. Gladstone, ib., (5), 31. 9, 1891; F. Swarts, Bull. Acad. Belgique, (3), 34. 293, 1897; Mem. Canr. Acad. Belgiqw , 61. 1901; C. Cuthbertson and E. B. R. Prideaux, PMI. Trans., 205. A, 319, 1905. I H M:oissan, Campt. Rend., 109. 937, 1889; C. de Wattcville, ib., 142. lO78, 1906; G. Salet, Ann. Chim. Phys., (4),28.34,1873. 6 P. Pascal, Campt. Rend., 152. 10lO, 1911; Bull. Sac. Chim., (4), 9. 6, I911. ? W. Abegg and C. E. lmmerwahr, Zeit. phys. Chem., 32. 142, 1900. 8 F. Kohlrauscb, Wied. Ann., 66. 785, 189ft 9 F. W. Skirrow, Zeit. anarfl. Chem., 33. 25, ] 903; M:. G. Levi, Chem. Ztg., 30. 4508, 1906; M. G. Levi and F. Ageno, Atti Accad. Lineei, (5), 15. ii, 549, 615, 1907. 19 H. M:oissan and J. Dewar, Campt. Rend., 124. 1202, 1894; 136. 641, 785, 1903. 11 O. Ruff and J. Zedner, Ber., 42. 1037, 1909; G. Gallo, Atti Aeead. Lincei, (5), 19. i, 295, 7.33, 19] O. 12 H. Moissan and P. Lebeau, Ann. Chim. Phys., (7), 26. 5, 1902. 13 H. M:oissan and P. Lebeau, Campt. Rend., 140. 1573, 1905. 1& H. Moissan, Le four electriqu.e, Paris, 1897; London, 1904; Compt. Rend., 110. 276, 1890; THE HALOGENS 15 D. Humiston, Journ. Phys. Chem., 23. 572, Hn9; W. L. Argo, :1<'. C. Mather , B. Humiston, and C. O. Anderson, ib., 23. 348, 1919. 15 H. Moissan, Ann. Chim. Phys., (6), 24. 224, I8\Jl. t6 H. Davy, Phil. Trans., 104. 64, 1814; J. J. Berzelius, Pogg. Ann., 8. 1, I82(); Ann. Chim. Phys., (2), 27. 53, 167,287, 1824; P. Louyet, ib., (3), 25. 291, 1849; E. F:r6rny, ib., (3),47. 15, I85G; J. B. A. Dumas, ib., (3),55. ]29, 1850; S. de Luca, Compt. Rend., 51. 299, 1860; H. Moissan, ilJ., 111. 570, 1890; O. T. Christensen, Journ. prakt. Chem., (2), 34. 41, 1886; (2),35. 54], ]887 ; J. Meyer, Zeit. aoorg. Chem., 36. 313, 1903; D. J. McAdam and E. F. Smith, Jour1 . Amer. Chem. Soc., 34. 592, 1912; .E. Moles and T. Batueeas, Journ. CMm. Phys., 17. 537, 1919; E. F. Smith and W. Ie van Haagen, The Atomic Wdghts of Boron and Fluorine, Washington, 1918. 17 C. W. Blomstrand, Die Chemie del' Jetztzeit, Heidelberg, 210, 340, ] 869; J. Thomsen, IVied. Ann., 138. 201, 1869; 139.217,1870; Ber., 3. 583,1870. 5. The Occurrence of Chlorine, Bromine, and Iodine ChIorine.-Chlorine does not occur free in nature, but hydrogen chloride has been reported in the fumes from the fumeroles of volcanic districts, 1 Vesuvius, Hecla, etc. D. Franco reported that the gases given off by the flowing lava of Vesuvius, during solidification, contained much hydrogen chloride, and the same gas has been found as an inclUBion in minerals. Hydrogen chloride is also found in the springs and rivers of volcanic districts-r..g. the Devil's Inkpot (Yellowstonc National Park), Paramo de Ruiz (Colombia), Brook Sungi Pait (Java), the Rio Vinagre (Mexico), etc. The latter is said to contain 0'091 per cent. of free hydrochloric acid which is estimated to be eq. to 42,150 kgrms. of HCI per diem. 2 J. B. J. D. Boussingault supposes this acid to be derived from the decomposition of sodium chloride by steam. Combined chlorine is an essential constituent of many minerals--there are sal ammoniac (ammonium chloride); Bylvine (potassium chloride); halite (sodium chloride); chlorocalcite, CaCI.; cerargyrite or horn silver, Agel; calomel, HgCI; terlinguaite, Hg.OCl; eglestoniUJ, Hg.CI.O; molysite, FeCl a ; erythrosiderite, 2KCl.FeCl a .H a O; rinneite, 3KCI.NaCl.FeCl a ; kremersite, 2KCI.2NH.CI.2FeCl a .3H.0; lawrencite, FeCI.; douglasite, 2KCI.FeC!a.2H.0; sccechite, MnCl.; cotunnite, PbCl.; matlockite, PbCl..PbO; penfleldite, 2PbCl..PbO; mendipite, PbCl a .2PbO; laurionite, PbCla.Pb(OH).; fledlerite, 2PbCl..Pb(OH).; rafaelite or paralaurionite, PbCl(OH); nantokite, CuCI; melanothallite, CuCl..CuO.H.O; hydro- meZanothallite, CuCl..CuO.2H.0; atacamite, CuaCI(OH).; percylite, PbCuCI(OH).; bole'ite, 3PbCuCI.(OH)..AgOl; footeUe, CuOl..8Cu(OH)a.4H.0; tallingite, CuCI..4Cu(OH)a.4H.0 ; atelite, CuCI..2Cu(OHJa,H.0; cumenge te, 4PbCl..4CuO.5H.0; pseudobolite, 5PbCl..4CuO. 6H 1 0; phosgenite, Pb.CI.CO a ; dauhre te, BiCla.2Bia03.3H.o; and in some Stassfurt minemls, carnallite, KCI.MgCI..6HaO; bischoflte, MgCl..6HaO; tachhydrite, CaOl a .2MgCl a . I2H.O; bomcite, MgCl..2MgaBsOIO; etc. Chlorine also occurs in mineral phosphates- e.g. it partially repla.ces fluorine in the chloroapatites-pyromorphite, (PbCl)Pb.(PO.Ja; mimetite, (PbCl)Pb.(AsO.Ja; and vanadinite, (PbCl)Pb.(VO.Ja. It occurs in pyrosmalite, H 5 (Fe,l\fn).EH.O t6 CI; sodalite, Na.Al a Si 5 0 12 C1, and other silicate mjnerals. Ohlorides occur in sea, river, and spring water, and small quantities in rain water. The ashes of plants and animals contain some chlorides. The gastric juices of animals contain chlorides as well as free hydrochloric acid. The 0'2 to 0'4 per cent. of free hydrochloric acid in the gastric juices of man is thought to play an important role in the digestion of food. 3 Sodium chloride occurs in blood and in urine; flesh contains potassium chloride; while milk contains both of the alkaline chlorides, with potassium chloride in large excess. According to R. Wanach,4 blood contains 0'259 per cent.. of chlorine, and serum, 0'353 per cent.; and according to A. J. Oarlson, J. R. Greer, and A. B. Luckhardt, there is still more chlorine in lymph. T. Gassmann found human teeth to contain 0'25-- to 0'41 per cent. of co.mbined chlorine, and the teeth of animals rather less. Bromine.-J. H. L. V ogt 5 estimates that bromine occupies about the 25th place in the list of elements arranged in the relative order of their abundance; and that the total crust of the earth has about 0'001 per ,cent. of bromine-the solid portion 0'00001 per cent. The ratio of bromine to chlorine is about the same in 8ea water and in the solid crust, and amounts to 1 : 150. The ratio of chlorides to 16 INORGANIC AND THEORETICAL CHEMISTRY bromides in marine waters of the globe is almost constant, excepting land-locked seas like the Black and Baltic Seas. It has been estimated that there are about 120000,000000 tons of bromides present in all the marine waters of our globe. The salt lake south of Gabes in Tunis has been worked since 1915 for bromine and potash. There is no record of the occurrence of free bromine in nature, but R. V. Matteucci 6 has reported the presence of hydrogen bromide in the fumeroles about VeRuvius. Bromine usually occurs as an alkali bromide or as silver bromide with more or less silver chloride and silver iodide. Thus, the Chilean mineral bromargyrite, bromyrite, or bromite approximates to AgBr; chlorobromosilver or embolite, Ag(CI,Br); and iodobromite, or iodoembolite, Ag(Cl,Br,I). Small quantities of these minerals occur in other places. Bromine has been reported in rock salt, meerschaum, and in French phosphorites by F. Kuhlmann; 7 in Silesian zinc ores by C. F. Mentzel and M. Cochler; in Chili saltpetre by H. Griineberg; in coal by A. Duflos; and in ammonia water and artificial sal ammoniac, by C. M1meand others. The Stassfurt salts contain bromides, indeed, these salts are the chief source of commercial bromine. s Perhaps two- thirds of the world's annual consumption of bromine (1,500,000 kilos) was obtained in Germany from these deposits. According to H. E. Boeke, the bromine in the Stassfurt deposits is there in the form of a bromo-carnallite, MgBr 2 .KBr,6H z O, in isomorphous mixture with carnallite MgCI 2 .KOI.6H 2 0. L. W. Winkler reported that the potash liquors of sp. gr. 1'3, from Stassfurt, Mecklenberg, and Hainleite respectively, have 7'492, 5'398, and 3'691 grms. per litre. Bischofite and tachhydrite from Vienenburg are the richest in bromine and contain respectively 0'467 and 0'438 per cent.; carnallite has 0'143 to 0'456 per cent.; sylvine, 0'117 to 0'300 per cent.; sylvinite, 0'085 to 0'331 per cent,; Hartsalz, 0'027 per cent.; and langbeinite, 0'016 per cent. The presence of bromides has been detected in numerous mineral and spring waters. There is a long list of reported occurrences of bromine in mineral waters in different parts of the world arranged alphabetically in L. Gmelin and K. Kraut's Handbuch der anorganischen Chemie (Heidelberg, 1. ii, 218, 1909). The waters of Anderton (Cheshire), Cheltenham (Gloucester), Harrogate (Y orkshire), Marston, Wheelock, and Winsford (Cheshire) are in the list for England. Some of the brine springs .g. the Congress and Excelsior Springs of Saratoga, N.Y.; Natrona (Wyoming); Tarentum (Pennsylvania); Mason City, Parkersville, etc. (West Virginia); Michigan, Pittsburg, Syracuse, Pomeroy, etc. (Ohio)-contain so large an amount of bromine that in importance they are second only to the Stassfurt deposits as sources of commercial supply; and they have played an important part in keeping down the price, and preventing the Stassfurt syndicate monopolizing the world's markets. The mineral waters of Ohio are said to contain the eq. of from 3'4 to 3'9 per cent. of magnesium brorriide. Bromine is present in sea water. The mixture of salts left on evaporation of the waters of the Atlantic Ocean contains from 0'13 to 0'19 per cent. of bromine-presumably as magnesium bromide; the Red Sea, 0'13 to 0'18; the Caspian Sea, 0'05; and the Dead Sea, 1'55 to 2'72 per cent. of bromine. 9 E. Marchand 10 has reported the presence of. traces of bromine in rain and snow. The ashes of many sea weeds and sea animals contain bromine-thus, dried Fucus vesiculosus contains 0'682 per cent. of bromine. l1 Bromine has been reported in human urine, salt herrings, sponges, and cod liver oil; but not in bone ash. Indeed, all products directly or indirectly derived from sea-salt or from Stassfurt deposits-- in the present or in the past-contain bromine. It is also said to be an essential constituent of the dye Tyrian purple which was once largely obtained from a species of marine gastropod or mollusc. Iodine.-Iodine is perhaps the least abundant of the halogens. Although widely distributed, it always occurs in small quantities. J. H. L. Vogt 12 estimates there is about 0'0001 per cent. of iodine in the earth's crust-the solid matter containing about 0'00001 per cent.; and the sea, 0'001 per cent. A. Gautier's estimate of the iodine in the sea is about one-fifth of this. Iodine occupies the THE HALOGENS 17 28th place in the list of elements arranged in their relative order of abundance, so that iodine has exercised no essential chemical or geological influence on the earth's surface. The sea appears to be the great reservoir of iodine. The ratio of bromine to iodine in Ilea water and in the solid crust is approximately the same, viz. from 1 : 10 to 1 : 12; and, in sea water, the ratio of chlorine to iodine is as 1 : 0'00012. L. W. Winkler reported] 7 mgrms. of iodine (as iodide) per litre of a natural saline water from Mecklenburg, that is, about 340 times as much as in sea water; a sylvinite mother-liquor from Alsace contained 0'5 mgrm. of iodine per litre. Iodine does not occur free in nature, althou!!h, according to J. A. Wanklyn,13 the waters of Woodhall Spa (Lincoln) are coloured brown by this element. R. V. Matteucci reported the occurrence of hydrogen iodide in the emanatIOns of Vesuvius, and A. Gantier found iodine in the gases disengaged from cooling lava. Iodine occurs along with bromine in iodobromite, Ag(Cl, Br, I); in iodyrite, AgI; marshite, CuI; coccinite, HgI 2 ; and in schwartzembergite, Pb(I,' Clh2PbO. Ac- cording to A. Guyard,14 the iodine-up to about 0'175 per cent. in Chile saltpetre- is present as sodium iodate, NaI0 3 , andperiodate, NaI0 4 ; H. Griineberg considers a double iodide of sodium and magnesium is also present. Potash saltpetre also has been reported to contain potassium iodate, KIO a , the caliche from which Chi]e saltpetre is extracted forms one of the most important sourceS of iodine; it contains about 0'2 per cent. of iodine, probably as sodium iodate. Iodine has also been reported in the lead ores of Catorce (Mexico); 15 in malachite-0'08 to 0'40 per cent. (W. Autenrieth); Silesian zinc ores (C. F. Mentzel and M. Cochler); the clay shales of Latorp in Sweden (J. G. Gentele); the limestones of Lyon and Montpellier (G. Lembert) ; the bituminous shales of Wurtemberg (G. C. L. Sigwart); the dolomites of Saxony (L. R. Rivier von Fellenberg); rock salt (0. Henry); the phosphorites of France (F. Kuhlmann); the phosphates of Quercy (H. Lasne); granites (A. Gautier); Norwegian apatite (A. Gautier); coal, and ammonium salts derived from coal (A. Duflos); guano of Cura<;ao (H. Steffens); and the Stassfurt salt deposits (A. Frank)-although F. Rinne and E. Erdmann failed to confirm A. Frank's resu]ts. The presence of iodides has al!!o been recorded in a number of spring waters, brines, etc. 16 In Great Britain it occurs in the waters of Leamington (Warwickshire), Bath (Somerset), Cheltenham (Gloucester), Harrogate (Yorkshire), Woodhall Spa (Lincoln), Bonnington (near Leith), Shotley Bridge (Durham), etc. Iodine occurs in small quantities in sea water; E. Sonstadt 17 estimated that there is about one part of calcium iodate per 250,000 parts of sea water; but according to A. Gautier, the iodine in the surface water of the Mediterranean Sea is found only in the organic matter which can be separated from the water itself by filtration; but at depths below 800 metres, he found iodine to be in water itself as soluble iodides. According to A. Gautier, also, the waters of the Atlantic contain 2'240 mgrlI1'>. per litre; and according to L. W. Winkler, the waters of the Adriatic Sea, 0'038 mgrm. per litre. A. Goebel reported 0'11 per cent. of iodine in the salts from Red Lake (Perekop, Crimea); and H. Fresenius 0'0000247 per cent. inthe waters of the Dead Sea. The amount is so small that analysts have usually ignored the iodine, or reported mere traces. Similar remarks apply to the brines from the waters of closed basins. Iodine has been reported in rain and snow,lB and A. Chatin found iodine uni- versally present in small quantities in the atm., rain water, and running streams. A. Gautier reported in 1889 that the air of Paris contained less than 0'002 mgrm. of free iodine or an iodine compound in about 4000 litres; but 100 litres of air in Paris contained 0'0013 mgrm. in a form insoluble in water, generally the spores of algoo, mosses, lichens, etc., suspended in the air. A. Gautier alsE} found sea air to contain 0'0167 mgrm. of iodine per 100 litres. The amount of iodine in mountain air and the air of forests is less than in other parts. The iodine in the atm. is supposed to be of marine origin. The presence of iodine as a normal constituent of the atm. has been denied,19 but A. Chatin's concluiiions were confirmed by J. A. Barral, A. A. B. Bussy, and A. Gautier. Marine animals and plants assimilate w a 0 18 INORGANIC AND THEORETICAL CHEMISTRY iodine from sea water; most of the iodine can be extracted by water from the ash of these organisms. It appears strange that the marine algre should select iodine from sea water and practically leave the bromine which is present in much larger proportions. The pelagic seaweeds (algre) in favourable localities cover the ocean about the lO-fathoms line with dense fields of floating foliage; the littoral seaweeds grow nearer shore at about the limit of extreme low tide. The deep-sea algre usually have a greater proportion of iodine than those which grow in shallow water. According to E. C. C. Stanford,2 0 the percentage amounts of iodine in a few dried plants are as follows: LITTORAL (SHORE) SEAWEEDS Fucus fllium Fucus digitatus Fucus nodosus . Fucus serratus . Fucus vesiculosus Ulva umbilicalis 0'089 0'135 0'057 0'085 0'001 0'059 PELAGIC (DEEP-SEA) Nereocystis leutkeana Macrocystis pyrifera Pelagophycus parra. Laminaria digitata . Larninaria stenophylJa Laminaria saccharina SEAWEEDS 0'521 0'205 0'24J. 0'374 0'478 0'255 A. M. Ossendowsky studied the algre employed in northern Japan for making iodine. According to J. Pellieux, seaweed grown in winter usually carries more iodine than that grown in summer; that grown in the north more than that grown in the south; and the younger parts of the algre more than in the older parts. Iodine has not been found in the gelatinous varieties of marine algre .g. the chondrus crwpus or Irish moss, and the eucheuma spinosum or agar-agar; nor has it been found in the enteromorpha compress a, or common sea-grass. Some plants which grow near the sea .9' the salsola kali, or salt-wort of salt-marshes, from which barillfS is made 21- a re almost free from iodine. Smaller amounts of iodine have been found in fresh-water plants than in land plants, and smaller proportions of potash are found in them also, According to A. Gautier,22 iodine must be a constituent of the chlorophyll or reserve protoplasm of plants because plants containing chloro- phyll contain more than the algre and fungi which are free from chlorophyll. Iodine is found in tobacco (A. Gautier), and in beetroot (lVI. J. Personne), and the potash derived from these products, as well as other plants, also contains iodine. It is found in fossil plants; and hence also its occurrence in coal, and in the ammoniacal products derived from coal. Turkey sponge has 0'2 per cent., the honeycomb sponge 0'054 per cent., and according to F. Hundeshagen,23 the sponges from tropical seas contain up to 14 per cent, of iodine; A. Fyfe, and K. Stratingh found none in corals; but E. Dreehsel isolated from certain corals what he considered to be iodogorgw acid, C 4 H s IN0 2 . Minute quantities of iodine have also been reported in nearly all marine worms, molluscs, fish, and other marine animals which have been examined. For example, oysters have been reported with 0'00004 per cent. of iodine; prawns, 0'00044; cockles, 0'00214; mussels, 0'03,57; salt herrings, 0'00065; cod-fish, 0'00016; and cod's liver, 0'00016 per cent. It occurs -i.n most fish oils-cod-liver oil, for in- stance, contains from 0'0003 to 0'0008 per cent. of iodine; whale oil has 0'0001 per cent. ; and seal oil, 0'00005 per cent. Iodine is a normal constituent of animals where it probably occurs as a complex organic compound. The iodine of the thyroidgland is present as a kind of albumen containing phosphorus and about 9 per cent. of iodine. This has been isolated by . digesting the gland with sulphuric acid, and precipitating with alcohol. The iodine seems to playa most important part ip the animal economy. The proportion of iodine is smaller in young people than in adults, and the amount becomes less and less with the aged. 24 According to J. Justus, the amount of iodine in milligrams per 100 grms..of the var-ious organs of human beings is: thyroid gland, 9'76 mgrms.; liver, 1'214; kidney, 1'053 j stomach, 0'989; skin, 0'879; hair, 0'844; nails, 0'800; prostate, 0'689; lymphatic gland, 0'600; spleen, 0'560; testicle, 0'500; pancreas, 0'431; virginal uterus, 0'413 j lungs, 0'320; nerves, 0'200; small THE HALOGENS 19 intestine, 0'119; fatty tissue, traces. The proportion in the corresponding parts of animals is smaller. Only a very small proportion is found in blood and l!lUscle. 0. Loeb 25 could find none in the brains, spinal marrow, fat, and bones. Iodme has been reported in wine and in eggs. E. Winterstein found no iodine in I?-ilk, cheese, or cow's urine; but he found iodine in thirty-five phanerogams-m beetroot, I<elery, lettuce, and carrots, but not in mushrooms or yellow boletus. REFERENCES. 1 R. Bunsen, Liebig's Ann., 62. I, 1847; D. Franco, Ann. CMm. Phys., (4), 30. 87, 1873 8 J. B. J. D. Boussingault, Compt. Rend., 78. 453, 526, 593, 1874; Ann. Chim. Phys., (5), 2. SO, 1874; F. A. Gooch and J. E. Whitfield, Bull. U.S. Geol. Sur., 47. 80, 1888. 8 P. SommmicId, Biochem. Zeit., 9. 352, 1908; J. Christiansen, ib., 46.2,1" 50, 71, 82, 1912. 4 R. Wanach, Chem. Centr., (4), 1. 355, 1889; T. Gassmann, Zeit. physiol. Chem., 55. 455, 1908; A. J. Carlson, J. R. Greer, and A. B. Luckhardt, Amer. Journ. Physiol. 23. 91, 1008. 5 J. H. L. Vogt, Zeit. prakt. Geol., 225, 314, 377, 413, 1898; 10, 274, 1899; F. W. Clarke, Bull. Wa8hill{/tnn Phil. Soc., 11. 131, 1889; Proo. Amer. Phil. Soc., 51. 214, 1912; W. Ackroyd, Chern. News, 86. 187, 1902. 6 R. V. Matteucci, Campt. Rend., 129. 65, 1899. 1 F. Kuhlmann, C(J1Inpt. Rend., 75. 1678, 1872; C. fIIene, ib., 30. 612, 1850; C. F. Mentzel, Kaatner's Archiv., 12. 252, 1827; M. Cochler, ib., 13. 330, 1828; A. Dufios, Arch. Pharm., 49. 29, 1848; H. Gruneberg, Journ. prak!. ahem", (1),60.172,1853. 3 K. Kubierschey, Die dcutsche Kaliindustrie. Halle a. S., 1907; L. W. Winkler, Zeit. angew. CMm., 10. 95, 1897; H. E. Boeke, ib., 21. 705, 1908; Sitzber. Akad. Berlin, 439, 1908. · F. W. Clarke, The Data of Geochemistry, Washingtcn, 1916. 16 E. Marchand, JO'/lIrn. Pharm. CMm., (3), 17. 356, 1850; T. Guareschi, Atti Accad. Torino, 47. 988, 1912. 11 F. Marsson, Arch. Pharm., 66. 281, 1851. 12 J. H. L. Vogt, Zeit. prakt. Geol., 225, 314, 377, 413, 1898; 100, 274, 1899; F. W. Clarke, Bull. Wa8hington Phil. Soo., 11. 131, 1889; Proc. Amer. Phil. Soc., 51.214, 1912; L. W. Winkler, Zeit. angew. Chem., 29. 451, 1916; A. Gautier, Bull. Soc. Chim., (3), 21. 450, 1899; W. Ackroyd, CMm. News, 86. 187, 1902. 18 J. A. Wanklyn, Chem. News, 54. 300, 1880; R. V. Matteucci, Compt. Rend., 129. 05, 1899; A. Gautier, ill., 129. 06, 189, 1899; H. Erdmann, Zeit. Naturwiss., 69. 47, 1896; R. Brandes, Sohweigger's Journ., 15. 32, 225, 1827; A. F. Bergeat, Zeit. prakt. Geol., 43, 1899; F. W. Dafert, Monatsh., 69. 235, 1908. U L. Faure, Chem. Gaz., 13. 199, 1855; Brit. Pat. No. 344, 1854; A. Guyard, Bull. Soo. Chim., (2), 22.60, 1874; V. A. Jacqnelain, Bull. Soc. Ene., 54. 652, 1855; H. Griineberg, Journ. pro!.:t. Ohem., (I), 60. 172, 1853. 15 W. Autenrieth, Zeit. ph?lsiol. Chem., 22.508,1897; Chem. Ztg., 23. 026, 1899; C. F. Mentzel, Kastner's Archiv., 12. 252, 1827; M. Cochler, ib., 13. 336, 1828; J. G. Gentele, Proc. Acad. StOOklwlm, 131, 1848; G. Lembert, Journ. Pharm., (3), 19. 240, I.B5I; G. C. L. Sigwart, Jahre.sb. Naturw. Wurtemberg, 43, 1853; L. R. Rivier von Fellenberg, Bull. Soc. Vaud. Scwn. Nat., 924, 1853; O. Henry, Jour'n. Chim. MM., (3), 5. 81, 1849; F. Kuhlmann, Compt. Rend., 75. 1078, 1872; T. Petersen, Jahrb. Min., 90,"1872; H. Lasne, Bull. Soc. Chim., (3), 2. 313, 1889; A. Gautier, Campi.. Rend., 129.60,1899; 132. 932, 1901; H. Steffens, Zeit anal. Chem., 19. 50, 1880; A. Dufios, Arch. Pharm., 49. 29, 1848; A. Frank, Zeit. angew. Chem., 20. 1279, 1907; }<'. Rinne, ib., 20. 1031,1907; E. ErdInann, ib., 21. 1693, 1908; H. E. Boeke, ib., 21. 705, ]908. 16 L. Gmelin and K. Kraut, HaruIbuch dcr anorganisohen Chemie, Heidelberg, 1. ii, 287, 1909. 17 E. Sonstadt, Chern. News, 25. 190,231,241, 1872; 74.310, 1896; A. Gautier, Campt. Rend., 128. 1009, 1899; 129. 9, 1899; A. Goebel, M ed. Chim. Phys., 5. 320, 1804; H. Fresenius, Verh. Ges. deut. Naf.urforflch. Aerzte, ll8, 1913; L. W. Winkler, Zeit. an1ew. Ohf!m., 29. 205, 1910. U E. Marchand, Oampt. Rend., 31. 495, 1850; A. Gautier, ib., 128. 643, 1899; A. Chatin, ib., 31. 868, 1850; 32. 069, 1851; 33. 529, 584, 1851; 34. 14, 51, 409, 519, 529, 584, 1852; 35. 40, 107,005, 1852; 37. 487, 723, 958, 1853; 38. 83, 1854; 39. 1083, 1854; 46. 399, 1858; 50. 420, 1860; 51.490, 1800; J. A. Banal, ib., 35. 427, 1852; A. A. B. Bussy, ib., 30 537, 1850; 35. 508, 1852. , 19 F. Garrigov, Compl.. Rend., 128. 884, 1899. . 80 E. C. C. Stanford, Chem. News, 35. 172, 1877; Dfngler's Journ., 226. 85, 1877; J. Pellieux, ib., 234. 210, 1879; A. Gautier, Compt. Rend., 129. 189, 1899; F. J. Cameron, Journ. Franklin Inst., 176. 340, 1913; A. M. Ossendowsky, Journ. Rltss. Phys. Chem. Soc., 38. 1081, 1900. 21 H. Davy, Phil. Trans., 104. 487, 1814; A. Fyfe, Edin. Phil. Journ., 1. 254, 1819. 22 A. Gautier, Compl.. Rend., 128. 043, 1069, IS99; 129. 60, 189, 1899; M. J. Personne, ib., SO. 478, 1850. 28 F. Hundeshagen, Zeit. angew. Chem., 8.473, 1895; K. Stratingh, Repert. Pharm., 15. 282, 1823; E. Drechsel, Centro Physiol., 9. 704, 1907; A. Fyfe, Edin. Phil. hum., 1. 254, 1819. 20 INORGANIC AND THEORETICAL CHEMISTRY 24 E. Baumann, Zeit. pllysiol. Ghem., 21. 319, 1895; 22. I, 1896; J. Justus, Virchow's Archiv, 170. 501, 1903; 176. I, 1904. 2> O. Loeb, Arch. Exp. Path., 56. 320, 18::17; H. Zenger, Arch. Pharm., (3), 6. 137, 1876; E. Winterstein, Zeit. physiol. Ghem., 104. 51, 1919. 6. The History of Chlorine. Bromine, and Iodine La vrai chimia ne date que de l'emp1oi bien p.tabli des acides mineraux, qui sont veri. tables dissolvants des metaux.-F. HOEFER (1842). Sodium chloride was known as salt from the earliest times. About 77 A.D., Pliny, in his Naturalis Historiw (33. 25), described the purification of gold by heating it with salt, misy (iron or copper sulphate), and schistos (clay). This mixture would give off fumes of hydrogen chloride. The attention, however, was focussed on the effect of the treatment on the metal; no notice was taken of the effiuvia. In the Alchimia Geberi (Bern, 1545)-supposed to have been written in the thirteenth century or afterwards-there is an account of the preparation of nitric acid by distilling a mixture of saltpetre, copp r sulphate, and clay; and Geber adds that the product is a more active solvent if some sal amrrwniacus is mixed with the in redients. Thus Geber prepared aqua regl:a. Raymond Lully 1 called the former aqua salis nitri, and the latter aqua salis armoniaci.. Albertus Magnus 2 called the first aqua prima (nitric acid), the second aqua secunda (aqua regia). J. R. Glauber (1648) 3 prepared aqua regia by distilling nitric acid with common salt. While the Arabian alchemists were probably acquainted with the mixture of nitric and hydrochloric acid known as aqua regia, there is nothing to show that they were acquainted with hydrochloric acid. The method of making hydrochloric acid, first called spiritus salis, dates from the end of the sixteenth century. Although there is no record, this acid was probab.ly made earlier than this because it was the custom of the then chemists to collect the products of the distillation of mixtures of various salts and earths; and the necessary ingredients were in their hands. For example, in preparing aqua regia it merely required the substitution of sal naturus for nitrum-which, as Pliny said, " do not greatly differ in their properties "-to furnish spiritus salis. It is almost inconceivable that this was not done. The preparation of the acid by distilling salt with clay is mentioned in the Alchemia (Francofurti, 1595) of A. Libavius; and in the Triumphwagen des Antimonii (Leipzig, 1624) of the anonymous writer Basil Valentine. J. R. Glauber (1648) described the preparation of spiritus salis by distilling common salt with oil of vitriol or with alum. J. R. Glauber also described the salient properties of this acid, and especially remarked on its solvent action on the metals. He mentioned that silver resists its action. H. Boerhaave knew that lead resists the action of the acid; R. Boyle referred to the action of the acid on soln. containing silver, and he noted,that the salt which this acid forms with the alkalies effervesces and fumes when treated with sulphuric acid. Stephen Hales (1727) noticed that a gas very soluble in water is given off when sal ammoniac is heated with sulphuric acid, and, in 1772, J. Priestley collected the gas over mercury and called it marine acid air in reference to its production from sea-salt. For a similar reason, the French term for the acid was acide marin. In A. L. Lavoisier's nomenclature (1787), the acid was designated acide muriatique, or muriatic acid.. and after H. Davy's investiga- tions on chlorine, the name was changed to aC1'de chlorhydrique or hydrochloric acid. There can be little doubt that the corrosive, suffocating, greenish-yellow fumes of chlorine must have been known onwards from the thirteenth century by all those who made and used aqua regia-e.g. J. R. Glauber's rectified spirit of salt mentioned above. Early in the seventeenth century, J. B. van Helmont mentioned that when sal marin (sodium chloride) or sal armeniacus (ammonium chloride) and THE HALOGENS 21 aqua chrysulca (nitric acid) are mixed together, a flatus incoerc£bile is evolved. J. Glauber (1648) also appears to have obtained a similar gas by heating zinc chloride and sand; he also said that by distilling spirit of salt with metal oxides, he obtained in the receiver a spirit the colour of fire, which dissolved all the metals and nearly all minerals. This liquid -was no doubt chlorine water; J. R. Glauber called it rectified spirit of salt, and he said that it can be used for making many products useful in medicine, in alchemy, and in the arts. He gives an example by pointing out that when treated with alcohol, spirit of salt furnishes oleum vim:, which is very agreeable, and an excellent cordial. The meaning of these observations was not understood until C. W. Scheele published his De magnesia nigra 4 in 1774. C. W. Scheele found that when hydro- chloric acid is heated with manganese dioxide, a yellowish-green gas, with a smell resembling warm aqua regia, is given off. C. W. Scheele's directions for preparing the gas are: Common muriatic acid is to be mixed with levigated manganese (i.e. pyrolusite) in any quantity in a glass retort, which is to be put into warm sand, and a glass receiver applied, capable of containing about. 12 oz. of water. Into the receiver put about 2 drms. of water; the joints are to be luted with a piece of blotting paper tied round them. In a quarter of an hour, or a little longer, a qnant[ty of the acid, going over into the receiver, gives the air contained in it a yellow colour, and then it is to be separated from the retort. He remarked that the gas is soluble in water; that it corroded corks yellow as if they had been treated with nitric acid; that it bleached paper coloured with litmus; that it bleached green vegetables, and red, blue, and yellow flowers nearly white, and the colour was not restored by treatment with acids or alkalies; that it converted mercuric sulphide into the chloride and sodium hydroxide, common salt; etc. O. W. Scheele considered the yellowish-green gas to be muriatic acid freed from hydrogen (then believed to be phlogiston); accordingly, in the language of his time, it was called dephlogisticated muriatic aC1'd. . A. L. Lavoisier (1789) 5 named the gas oxymuriatic acid, or oxygenated muriatic acid, because he considered it to be an oxide of muriatic (i.e. hydrochloric) acid; and, consistent with his oxygen theory of acids, A. L. Lavoisier considered muriatic acid to be a compound of oxygen with an hypothetical muriatic base-murium ; this imaginary element was Jatersymbolized Mu; hydrochloric acid was symbolized Mu02; and C. W. Scheele's gas, Mu03' Hence, added A. L. Lavoisier, muriatic and oxymuriatic acids are related to each other like sulphurous and sulphnric acids; and he was at first in- clined to call the one acide muriateux, and the other acide munatique. This certainly seemed to be the most plausible explanation of the reactions. Lavoisier's hypothesis was supported by an observation of C. L. Berthollet (1785),6 that if the manganese dioxide be deprived of some of its oxygen by calcination, it furnishes a much smaller quantity of Scheele's gas. Hence, concluded C. L. Berthollet, "it is to the vital air (oxygen) of the manganese dioxide, which combines with the muriatic acid, that the formation of dephlogisticated marine acid is due." He did not succeed in oxidizing muriatic acid to oxymuriatic acid, because he considered that the elastic state of muriatic acid gas prevents it uniting directly with oxygen. However, O. L. Berthollet supposed that he had succeeded in decomposing dephlogisticated marine acid into muriatic 'acid and oxygen, for he noticed that an aq. soln. of O. W. Scheele's gas-the so-called oxymuriatic acid-when exposed to sunlight, gives off bubbles of oxygen gas, and forms muriatic acid. In 1800, W. Henry 7 passed electric sparks through muriatic acid gas and obtained a little hydrogen which he supposed to come from the moisture in the gas; ou sparking a mixture of oxygen and muriatic acid gas he obtained a little oxymuri- atic acid gas which he supposed was formed by the electric sparks decomposing some of the moisture in the muriatic acid gas into oxygen, and the union of the oxygen with the muriatic acid gas to formoxymuriatic acid gas. The experiments 22 INORGANIC AND THEORETICAL CHEMISTRY of J. L. Gay Lussac and L. J. TMnard,B and the earlier experiments (1809) of H. Davy,9 were complicated by the assumption that muriatic acid gas contains water, or the principles which constitute water, intimately combined. According to J. L. Gay Lussac and L. J. TMnard, muriatic acid gas and oxygen are formed when a mixture of steam and oxymuriatic acid is passed through a heated porcelain tube. It was here assumed that the muriatic acid gas in virtue of its great affinity for water, leaves the oxygen with which it is combined in oxymuriatic acid gas, and combines with the water to form muriatic acid gas. L. J. Gay Lussac and L. J. TMnard also found that by heating a mixture of hydrogen and oxymuriatic acid gas, there is a " violent inflammation with the production of muriatic acid" ; they also showed that a mixture of equal volumes of hydrogen and oxymuriatic acid gas does not change in darkness, but in light, the mixture is transformed into muriatic acid; and in bright sunlight, the combination is attended by a violent explosion. It was assumed in these experiments that water is formed by the hydrogen removing the necessary oxygen from oxymuriatic acid gas, and leaves behind muriatic acid gas which is eager to combine with water. J. L. Gay Lussac andL. J. TMnard also tried to deoxidize oxymuriatic acid, so as to isolate the hypo- thetical muriatic base of A. L. Lavoisier, by passing the dry gas over red-hot carbon, but when the carbon was freed from hydrogen no change was observed even though " urged to the most violent heat of the forge." In any case, the attempt to separate from oxymuriatic acid anything but itself was a failure. While favouring Lavoisier's hypothesis, J. L. Gay Lussac and L. J. TMnard added: "the facts can also be explained on the hypothesis that oxymuriatic acid is an elementary body." Here, then, are two rival hypotheses as to the nature of oxymuriatic acid-the yellowish- green gas discovered by Scheele! According to C. W. Scheele's hypothesis, oxy- muriatic acid=muriatic acid less hydrogen; according ,to C. L. Berthollet and A. L. Lavoisier's hypothesis, oxymuriatic acid=muriatic acid plus oxygen. In his Researches on the Oxymuriatic Acid (1810), H. Davy described the attempts which he'made, without success, to decompose oxymuriatic acid gas. He also found that when dried muriatic acid gas is heated with metallic sodium or potassium, the metallic muriate and hydrogen are formed, but neither water nor oxygen is obtained. Hence, no oxygen can be found in either muriatic acid gas or oxymuriatic acid gas. H. Ziiblin also tried in 1881, and likewise failed to decompose chlorine. Accordingly, H. Davy claimed that C. W. Scheele's yjew is an expression of the facts, while Lavoisier's