The red pigment vermilion is obtained by grinding natural cinnabar or synthetic mercuric sulfide. Zinc is also commonly amalgamated using mercuric chloride. Mercury occurs in deposits throughout the world mostly as cinnabar (mercuric sulfide). Mercury batteries use a reaction between mercuric oxide and zinc electrodes in an alkaline electrolyte. It reacts with chlorine to give mercuric chloride, which resists further oxidation. The reaction is also common with red ink, which may contain cinnabar (mercuric sulphide). These include calomel (mercurous chloride), and mercuric chloride. Syphilis was frequently treated with mercuric chloride before the advent of antibiotics. Objects in drawers were protected by scattering crystalline mercuric chloride over them. It forms when an aqueous solution of iodine is treated with mercuric or silver salts. These included carbon dioxide by burning diamond, and mercuric oxide by heating mercury. He used electrolysis on a mixture of magnesia and mercuric oxide. She bought an entire box of mercuric chloride tablets. Cupric sulfate was not as efficient as mercuric oxide, and yielded lower protein results. It can be best prepared by heating mercuric cyanide.