NOTES ON THE CHLORIDES OF IRON. 
403 
sp. gr. T5.* So, then, the Pharmacopoeia directions include the use of a slight 
excess of hydrochloric acid, and nearly half as much more nitric acid as is theore¬ 
tically necessary. The excess, and more too, of the hydrochloric acid escapes when 
the solution of perchloride of iron is concentrated by evaporation, and its place is 
supplied to some extent by the superfluous nitric acid. If, however, the excess 
of nitric acid were omitted, and its place not supplied by additional hydro¬ 
chloric acid, the amount of peroxide of iron formed during ebullition would be 
too large for resolution in the residual perchloride. As before remarked, the Phar¬ 
macopoeia adaptation of the nitro-hydrochloric process of preparing perchloride of 
iron is a failure, in so far as the production of an aqueous solution of pure perchlo¬ 
ride of iron is concerned. I may state that by using the theoretical quantity of 
nitric acid and about an ounce more hydrochloric acid than is theoretically ne¬ 
cessary, I have succeeded in producing solutions of perchloride of iron of the 
officinal strength, containing no nitric acid, but varying in the amount of hy¬ 
drochloric in the products, and consequently producing, when mixed with spirit 
of wine, liquids*which may or may not be stable. The action of the excess of 
acid is, as already indicated, to replace hydrochloric acid lost by evaporation, 
and to decompose excess of nitric acid. 
Fourth Method. 
The fourth process for preparing solution of perchloride of iron to which I 
shall refer is that of dissolving peroxide of iron in hydrochloric acid. This pro¬ 
cess has been extolled for its simplicity. Gentlemen knowing nothing of che¬ 
mical manipulation could dissolve the oxide in the acid, much as they would 
dissolve sugar in water, and enjoy the self-satisfaction of having made their own 
preparation ; forgetting that the peroxide had probably to be prepared from a per- 
salt, and that the persalt had to be made from a protosalt by the agency of nitric 
acid, and that the process was therefore not very different from apparently more, 
but really less complicated processes. I should advise such persons to go one step 
further than getting their wholesale chemist to thus perform half the process for 
them, and they complete it; I should advise them to let the manufacturer per¬ 
form the ■whole operation. For if manipulators should never attempt to make 
any hydrochloric solutions of definite strength unless they can ascertain for 
themselves the strength of the aqueous acid by taking its specific gravity, surely 
they should not endeavour to prepare perchloride of iron from two substances, 
of which aqueous hydrochloric acid is one, and the other a body of equally in¬ 
constant qualities, namely, the so-called peroxide of iron. If a purchased speci¬ 
men of peroxide of iron be only what its name indicates, it will most likely be 
in such a physical state as to be insoluble, or only partially soluble, in hydro¬ 
chloric acid. And if it be readily soluble in the acid, it will probably be a hy¬ 
drated oxide of iron, containing an inconstant amount of water.f In adopting 
this process, therefore, an inexperienced manipulator is more likely to make 
errors than in any other. lie will probably fail in making his solution of per¬ 
chloride of iron, or, if succeeding, his product will probably either be so basic as 
decompose a few days after mixing with spirit, or so acid as to mislead or be 
condemned by the prescriber. Of course an operator having knowledge and 
* Data. Fe = 28; N0 5 = 54; II Cl = 36’5. Aqueous hydrochloric acid of sp. gr. 1T7 contains 
34'25 per cent, of anhydrous acid (Ure). Aqueous nitric acid of sp. gr. 1*5 contains 79‘7 per¬ 
cent. of NO s (Ure); 1 fl. oz. = 437’5 grains; 1 fl.drachm = 54*6875 grains; 1 minim = -9114583 
grain. The presence of carbon in the iron is not taken into account, an experiment showing 
it to exist only in the proportion of ‘25 per cent. 
f The last sample supplied to me for laboratory use by one of the most respectable of the 
London manufacturers, contained only 67 instead of 90 per cent, of oxide, the remainder being 
sulphate of ammonia and water. Even this badly washed and dried specimen was not wholly 
soluble in hydrochloric acid. 
