400 
PHARMACEUTICAL MEETING. 
manganese and heat. If, however, the salt be required in solution only, two- 
thirds of the chlorine can be obtained from the hydrochloric acid without either 
heat or binoxide of manganese, and two-tliirds of the necessary labour, as well 
as of the heat and manganese, are thereby saved. In this case the iron is at 
once placed in two-thirds of the total amount of hydrochloric acid required ; in 
a few hours the hydrogen of the acid has been wholly displaced by the iron, and 
has bubbled or effervesced out of the liquid, escaping, in the gaseous state, into 
the air. The result is a solution of proto -chloride of iron; beyond this point 
iron will not decompose hydrochloric acid. The other third portion of the 
hydrochloric acid is then made to yield its chlorine as before, by heating with 
binoxide of manganese, and this chlorine, conducted into the solution of proto¬ 
chloride already formed directly from the acid, converts the protosalt into a 
pure solution of perchloride of iron. To make this solution of the officinal 
strength, rather more than two ounces of fine iron binding-wire are placed in a 
mixture of six-and-a-half fluid ounces of hydrochloric of sp. gr. T17, andthree- 
and-a-half ounces of water (or seven fl. oz. of acid of sp. gr. 1T6 and three oz. 
of water), and the whole placed in a flask or bottle, or some other vessel from 
which gas can escape, without the solution being unduly exposed to the air. In 
the summer time decomposition is complete in less than a day, in winter the 
vessel must be set in a warm place ; for this is an action in which the chemical 
force is much influenced by the force of heat. The carbonaceous residue of the 
iron and the iron not dissolved must now be separated as quickly as possible, by 
filtering the solution into a bottle, and then chlorine gas be passed into the 
liquid until the protochloride of iron is entirely converted into perchloride. This 
is ascertained by placing a drop of the solution in thirty or forty drops of water, 
and adding solution of ferridcyanide of potassium, which gives a dark precipi¬ 
tate of Prussian blue with protosalts, but only darkens the colour of the liquid 
if persalt alone is present: when, therefore, a dark-blue precipitate ceases to be 
formed, the reaction is complete. Towards the end of the operation the de¬ 
livery-tube must be removed, the stopper placed in the bottle, and the contents 
well shaken occasionally, in order to aid the contact of the chlorine with the 
last portions of protochloride. More chlorine is required in this operation than 
is theoretically necessary, as a portion of each bubble passes up through the 
liquid and escapes before it and the protochloride have time to attack each other. 
Finally, excess of chlorine dissolved in the solution is got rid of by boiling the 
liquid. Here, however, the process breaks down. The last traces of chlorine 
are not removed till the ten ounces of solution have been reduced to eight, and 
during the ebullition much hydrochloric acid is lost. In appearance the pro¬ 
duct is excellent, but it is of course very basic. 
Third, Method. 
The third process for preparing perchloride of iron to which I shall refer, is a 
slight modification of the one already described. It is that adopted by the com¬ 
pilers of the British Pharmacopoeia. As in all the other processes, so in this, the 
required chlorine is obtained from hydrochloric acid. But the hydrogen of the 
acid is not removed either wholly, as in the first-named process, nor partially, 
as in the second, by the agency of binoxide of manganese and heat, but by 
nitric acid. Iron is dissolved in the requisite quantity of hydrochloric acid, two- 
thirds of which, as already described, loses its hydrogen in the gaseous state, and 
protochloride of iron is formed :— 
Fe 2 + 3HCl = 2FeCl + HCl + H 2 . 
On the addition of nitric acid, the third portion of hydrochloric acid loses its 
hydrogen by the action of some of the oxygen in the nitric acid, and the libe¬ 
rated chlorine then combines with the protochloride of iron to form perchloride:— 
HC1 +0 = H0 + C1; 
then 2FeCl -j- Cl = Fe 2 C] 3 . 
