MERCURY, PROTOCHLORIDE OF. This compound, so much used by medical practitioners, is commonly prepared by triturating four parts of corrosive subli mate along with three parts of running quicksilver in a marble mortar, till the metallic globules entirely disappear, with the production of a black powder, which is to be put into a glass balloon, and ex posed to a subliming beat in a sand bath. The calomel, which rises in vapor, and attaches itself in a crystalline crust to the upper hemisphere of the balloon, is to be detached, reduced to a fine powder, or levigated and elutriated. 200 lbs. of mer cury yield 206 of calomel and 272 of cor rosive sublimate.
The following more economical process is that adopted at the Apothecaries' Hall, London. 140 pounds of concentrated sul phuric acid are boiled in a cast-iron pot upon 100 pounds of mercury, till a dry phosphate is obtained. Of this salt, 124 pounds are triturated with 81 pounds of mercury, till the globules disappear, and till a protosulphate be formed. This is to
be intimately mixed with 68 pounds of sea-salt, and the mixture, being put into a large stone-ware cucurbit, is to be sub mitted to a subliming heat.
From 190 to 200 pounds of calomel rise in a crystalline cake, as in the former pro cess, into the capital; while sulphate of soda remains at the bottom of the alem bic. The calomel must be ground to an impalpable powder, and elntriated. Tho vapors, instead of being condensed into a cake within the top of the globe or in a capital, may be allowed to diffuse them selves into a close vessel, containing wa ter in a state of ebullition, whereby the calomel is obtained at once in the form of a washed impalpable powder. Calomel is tasteless and insoluble in water. Its specific gravity is 7.176.