SULPHATE OF ZINC.
527
Zin'ci Sulphas.—Sulphate of Zinc.
History. —This salt is said by Schwartze ( Pharm. Tabell. 2 ,e Ausg.779), to have been known towards the end of the 13th, or at the com-mencement of the 14th century ; but Beckmann affirms it was not knownbefore the middle of the 16th century [Hist, of Invent, iii. 85). It hashad various names, as sal vitrioli, white vitriol, and Gilla Theophrasti.
Natural History. —It occurs native at Rammelsberg, near Goslar ,in the Harz ; at Holywell, in Flintshire ; and other places.
Preparation. —It is readily prepared by dissolving zinc in dilutedsulphuric acid. The proportions, directed to be used in the LondonPharmacopoeia, are five ounces of zinc and two pints of diluted sulphuricacid. The solution is to be fdtered, evaporated, and crystallized. Inthis process 1 equivalent or 9 parts of water are decomposed, anequivalent or 1 part of hydrogen escapes, while an equivalent or 8 partsof oxygen unite with 1 equivalent or 32 parts of zinc, to form1 1 equivalent or 40 parts of the oxide, which, with 1 equivalent or40 parts of sulphuric acid, form 1 equivalent or 80 parts of the sulphate.(The zinc and the oxide thus formed combines with some sulphuric acid) to form the sulphate.
REAGENTS.
l M Water o $ 1 e< p Hydrogen 1-
1 eq. water » eq- Oxygen .. 8 , .
1 eq. Zinc .32 >
RESULTS.
-1 eq. Hydrogen.
eq. Ox. Zinc 40_
=,1 eq. Sulphate of Zinc
1
80
By roasting blende (sulphuret of zinc) in reverboratory furnaces animpure sulphate is obtained, which is lixiviated, and the solution con-centrated by evaporation, so that on cooling it forms a crystalline massresembling lump sugar. This is distinguished among druggists by thename of white vitriol, a term which they confine to this commoner kindof sulphate. This impure salt contains iron, and usually copper and lead.
Properties. —The primary form of the crystals of sulphate of zinc isthe right rhombic prism : they are transparent and colourless, and havea metallic astringent taste. They are soluble in 2^,% times their weightof cold water, and less than their own weight of boiling water. They areinsoluble in alcohol. In dry and warm air they effloresce. Whenheated they undergo the watery fusion; and if the liquid be rapidlycooled, it congeals into a granular, crystalline, white mass : if the heatbe continued the salt becomes anhydrous, and, at an intense heat, isdecomposed, leaving a residue of zinc.
Characteristics. —That this salt is a sulphate, is proved by the actionof chloride of barium on it; a white precipitate is produced, insoluble innitric acid. Acetate of lead also occasions a white precipitate. Thepresence of oxide of zinc in the solution is recognized by the testsalready mentioned (p. 999 .)
Composition.— This salt has the following composition:—
Eq. Eq. Wt. Per Cent. Berzelius Mitscherlich.Oxide of Zinc . . . . 1 . . 40 . . . 28 . . . 32*585 . ?
Sulphuric Acid . . . . 1 . . 40 . . . 28 . . . 30*965 . f
Water. 7 . . 63 . . . 44 . . . 36*450 . . . 44*76
Crystallized Sulphate of Zinc 1 . . 143 . . . 100 . . . 100*000 . . . 100*00
Purity.—A mmonia added to a solution of sulphate of zinc throwsdown the hydrated oxide of zinc ; excess of ammonia re-dissolves the