10 
PHYSICAL AND CHEMICAL PROPERTIES. 
According to the United States Pharmacopoeia, chloride of zinc 
(ZnClg), 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 owing to its hygroscopic character should 
be kept in bottles closed with paraffin. It is possessed of dehydrating 
powers, removing oxygen and hydrogen from organic matter in the 
form of water, which probably accounts for what influence 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. Pharmacopoeia prescribes the limit of this by 
directing that 1 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 volume of alcohol. 
In somewhat aqueous solutions zinc chloride undergoes partial hydrol- 
ysis, the precipitate consisting of basic or hydroxy-chlorides, e. g. , 
ZnCl,+H,0 =HC1+Zu|^|^. 
This flocculent 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 II. 1 c. c. 
of a decinormal silver solution to produce a permanent red color. 
^Vhen heated to 115° 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 i*esidue 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 afl'ected after thirty daj^s 
exposure in a 100 per cent solution of zinc chlorid, but the same 
strength solution gradually destrovs 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 Pharmacopceial solution of zinc chloride (liquor zinci chloridi) 
has a specific gravity of about 1.535 at 15° C. and contains about 50 
per cent by weight of the salt. ' 
