10 
PHYSICAL AND CHEMICAL PROPERTIES. 
According to the United States Pharmacopoeia, chloride of zinc 
(ZnCh), as found on the market, is a white, granular, friable, translu- 
cent powder or porcelain-like masses, irregular, or molded into pencils, 
odorless, and of such intensely caustic properties as to make tasting- 
dangerous unless the salt be diluted, when it has an astringent, metallic 
taste. 
It is very deliquescent, and oAving to its hygroscopic character should 
be kept in bottles closed with paraffin. It is possessed of dehydrating 
powers. remo' ing oxygen and hydrogen from organic matter in the 
form of water, which probably accounts for what inlluence it exerts 
as an antiseptic and germicide. It is soluble in about 0.3 part of 
water at 15^ C., forming a clear, viscid solution, which on boiling- 
deposits a basic salt. 
It is practically impossible to obtain zinc chloride entirely free from 
basic salt, and the U. S. Pharmacopceia prescribes the limit of this by 
directing- that I drop of hydrochloric acid shall clear up opacity caused 
in 5 c. c. of a 5 per cent aqueous solution of the salt by the addition of 
an equal Amlume of alcohol. 
In somewhat aqueous solutions zinc chloride undergoes partial hydrol- 
ysis. the precipitate consisting of basic or hydroxy-chlorides, e. g.. 
ZnClg-^H.jO =HC1— Znj^^. This llocculent precipitate can be cleared 
by the careful addition of dilute hydrochloric acid. 
The U. S. Pharmacopoeia requires that the official salt contain not 
less than 99.81 per cent of zinc chloride. This can be determined by 
dissolving- 0.3 gram of dry chloride of zinc in 10 c. c. of water and 
adding- 2 drops of chromate of potash, when it should require Id. I c. c. 
of a decinormal silver solution to produce a permanent red color. 
AVhen heated to II5-- C.. zinc chloride fuses to a clear liquid. At a 
higher temperature it is partly volatilized in dense, white fumes and, 
in part, decomposed, leaving a residue of zinc oxide. 
The aqueous solution turns blue litmus paper red. 
A 5 per cent solution produces no corrosive action on iron, brass, 
wood, or caoutchouc, and. it is said, does not rot ordinary fabrics, but 
causes a reddening and smarting- sensation when applied to the skin. 
Linen threads and hair are not apparently aliected after thirty days 
exposure in a 100 per cent solution of zinc chlorid. but the same 
strength solution gradually destroys cotton and silk threads. This 
destruction is so complete at the end of ten or eleven days that no 
evidence of the presence of these materials in the solution is observable. 
The Pharmacopoeial solution of zinc chloride (liquor zinci chloridi) 
has a specitic gravity of about 1.535 at 15^ C. and contains about 50 
per cent by weight of the salt. 
