The depolarizer is a paste of mercurous sulfate. He used a mercury electrode along with a mercury/mercurous nitrate reference electrode. There was no way of knowing how much mercurous chloride each dose contained. According to Scherer, could be obtained by reaction of mercurous nitrate and sodium thiosulfate . Mercury can strip off fluoride to make thionyl fluoride and mercurous fluoride. Over-the-counter medicines have been shown to have traces of mercurous chloride. These include calomel (mercurous chloride), and mercuric chloride. However, the existence of mercurous sulfide was disputed in 1816 by French pharmacist N. Guibourt. Mercuric nitrate can be reacted with elemental mercury to form mercurous nitrate. I (mercurous mercury), and II (mercuric mercury). He titrated mercurous solution with potassium chloride, potassium bromide, and potassium iodide. Mercurous chloride decomposes into mercury(II) chloride and elemental mercury upon exposure to UV light. Above this was the mercurous sulfate paste and, above that, the zinc sulfate solution.