702 POISONS : THEIR EFFECTS AND DETECTION. [§§ 895 - 897 . 
at a bright red heat it fuses, and then volatilises, the fumes taking fire 
when exposed to the air. In analysis, zinc occurs either as a metallic 
deposit on a platinum foil or dish, or as a brittle bead, obtained by 
reducing a zinc compound with soda on charcoal. 
According to Delezenne (Ann. Inst. Pasteur , 1919), zinc is a constant 
constituent of all animal cells. In the venom of serpents it is present 
to the extent of 0-31 to 0-56 per cent. 
The salts of zinc to be briefly described here are the carbonate, the 
oxide, and the sulphide—all of which are likely to occur in the separa¬ 
tion and estimation of zinc, and the sulphate and chloride—salts more 
especially found in commerce, and causing accidents from time to time. 
§ 895. Carbonate of Zinc, in the native form of calamine, contains, as 
is well known, 64-8 per cent, of oxide of zinc ; but the carbonate obtained 
in the course of an anatysis by precipitating the neutral hot solution of 
a soluble salt of zinc by carbonate of potash or soda, is carbonate of zinc 
plus a variable quantity of hydrated oxide of zinc. Unless the precipi¬ 
tation takes place at a boiling temperature, the carbonic anhydride retains 
a portion of the oxide of zinc in solution. By ignition of the carbonate, 
oxide of zinc results. 
§ 896. Oxide of Zinc (Zn0 = 81 ; specific gravity, 5-612; Zn 
80-24, 0 19-76) is a white powder when cool, yellow when hot. If 
mixed with sufficient powdered sulphur, and ignited in a stream of 
hydrogen, the sulphide is produced ; if ignited in the pure state in 
a rapid stream of hydrogen gas, metallic zinc is obtained ; but, if it 
is only a feeble current, the oxide of zinc becomes crystalline, a portion 
only being reduced. 
§ 897. Sulphide of Zinc (ZnS = 97 ; specific gravity, 4-1 ; Zn 67-01, 
S 32-99).—The sulphide obtained by treating a neutral solution of a 
soluble salt of zinc by hydric sulphide is hydrated sulphide, insoluble in 
water, caustic alkalies, and alkaline sulphides, but dissolving completely 
in nitric or in hydrochloric acid. When dry, it is a white powder, and 
if ignited contains some oxide of zinc. The anhydrous sulphide is pro¬ 
duced by mixing the precipitated sulphide with sulphur, and igniting in 
a crucible in a stream of hydrogen gas. 
Pharmaceutical Preparations. —The official compounds of zinc 
used in medicine are the acetate, carbonate, chloride, oxide, sulphate, 
sulpho-carbolate, oleate, and valerianate. 
Sulphate of Zinc (ZnS0 4 7H 2 0 = 161 + 126 ; specific gravity, crystals, 
1-931).—This salt is official in all the pharmacopoeias, is used in 
calico-printing, and is commonly known as white vitriol. By varying 
the temperature at which the crystals are allowed to be formed, it 
may be obtained with 6, 5, 2, or 1 atoms of water. The commercial 
sulphate is in crystals exactly similar to those of Epsom salts ; it is 
slightly efflorescent, and gives the reactions of zinc and sulphuric acid. 
