404 
PHARMACEUTICAL MEETING. 
skill would produce a perfectly pure solution of perchloride of iron of definite 
strength from peroxide of iron and hydrochloric acid, for he would use only the 
hydrated peroxide, ascertaining its value by igniting a weighed quantity, and 
weighing the residue, and from these data calculating the amount of anhydrous 
peroxide in it; would determine the strength of the acid by its specific gravity; 
and finally, would mix the oxide and acid in such proportions as to ensure neu¬ 
trality and exact percentage composition.* But even under those circumstances 
the solution could not be made of the officinal strength, for the requisite quan¬ 
tity of peroxide of iron increases the bulk of the strongest hydrochloric acid to 
an extent that necessitates subsequent concentration, and then, of course, hy¬ 
drochloric acid is lost, the resulting solution is basic and decomposes on being 
mixed with three times its bulk of spirit to form the tincture. Obviously this is 
a difficulty that would not occur if a more dilute solution were required,—a solu¬ 
tion, for example, of one-fourth the strength—of the strength, in fact, of the 
officinal tincture. Under any circumstances, however, the operator must make 
his own hydrated peroxide; so that, altogether, he would probably prefer the 
direct and, to him, less troublesome process of preparing his solution from the 
anhydrous perchloride. 
Other Methods. 
There are other methods by which it is possible to produce perchloride of 
iron, but they are of theoretical interest only, and therefore need not be 
noticed. 
The process of the United States Pharmacopoeia is similar to that of the 
British Pharmacopoeia, except that an indefinite quantity of nitric is ordered ; 
the nitric acid is to be added to the hot acid solution of protochloride of iron, 
until effervescence is no longer produced. The product will consequently con¬ 
tain much free nitric acid, for the black compound of binoxide of nitrogen and 
protochloride of iron is not decomposed in a neutral or only slightly acid solu¬ 
tion. 
Crystallized hydrated perchloride of iron, containing twelve atoms of water of 
crystallization, is sometimes ordered in prescriptions. It occurs in yellow 
masses having a crystalline structure, and is formed when solution of perchloride 
of iron is concentrated to a thick syrup, and set aside to cool. It is seldom pure, 
containing excess of acid or base, and varying somewhat in the amount of water 
it may contain. Being itself indefinite, it cannot be used in forming a definite 
solution. 
Conclusion. 
In conclusion, let me briefly recapitulate the chief points in the chemistry of 
the chlorides of iron to which I wish to draw attention. First, cold aqueous solu¬ 
tions of pure perchloride of iron are perfectly stable, and can be prepared of defi¬ 
nite strength. Second, spirituous solutions, either wholly alcoholic or containing 
water, are unstable, and soon lose their definite character. Third, the presence 
of hydrochloric acid retards the decomposing reaction of perchloride of iron and 
alcohol. Fourth, no process for the preparation of pure solution of perchloride 
of iron is so simple as to be capable of performance without chemical knowledge 
and skill. Fifth, solutions of either of the chlorides of iron are partially decom¬ 
posed on evaporation, and protochloride of iron is volatile in the vapour of 
water. Sixth, neither the process of the British Pharmacopoeia nor that of the 
London Pharmacopoeia yields a pure solution of perchloride of iron. Seventh, 
the method of producing solution of perchloride of iron by saturating hydro¬ 
chloric with iron, and passing excess of chlorine through the resulting liquid, 
is faulty, because the excess of chlorine cannot practically be removed ex- 
* See a paper by Davenport, Pliarm. Journ. 2nd ser. vol. iv. p. 362. 
