199 
ON AQUEOUS SOLUTIONS OE PERCHLORIDE OF IKON, SUCH 
AS LIQUOK EERRI PERCHLORIDI, B.P. 
BY J. ATTFIELD, PII.D., F.C.S. 
There are four ways of making an aqueous solution of perchloride of iron, 
but only one of these gives it in a pure state. To obtain it absolutely pure, the 
solid anhydrous perchloride—made directly from its elements, chlorine and iron 
—is simply dissolved in distilled water. This is the method analytical chemists 
adopt. The practical results of the other methods is to give a solution of per¬ 
chloride of iron, containing either peroxide of iron or hydrochloric acid. The 
first of these three faulty processes is that of saturating aqueous hydrochloric 
acid by iron, and then passing chlorine through the solution till the proto¬ 
chloride of iron is converted into perchloride. The result is a liquid loaded 
with free chlorine. It is true the chlorine can be removed by ebullition, 
but simultaneously the perchloride of iron and water react, hydrochloric acid is 
produced and lost, and peroxide of iron remains to contaminate what remains of 
the perchloride. The second of the faulty methods is to dissolve peroxide of 
iron in aqueous hydrochloric acid; it fails because pure soluble peroxide of iron, 
in a definite state of hydration, is not met with in commerce. And the remain¬ 
ing faulty process is to saturate two-thirds of a given volume of hydrochloric 
acid by iron, and then remove the hydrogen of the other third by nitric acid. 
This fails, because heat is necessary to complete the reaction ; and with heat de¬ 
composition of the perchloride of iron and loss of hydrochloric acid to an un¬ 
known extent occurs.* These three faulty methods are those commonly adopted 
by manufacturing chemists. 
But why is the presence of peroxide of iron or of hydrochloric acid in aqueous 
solution of perchloride of iron to be considered a fault ? Without touching the 
sesthetical or moral aspects of the question, the answer is as follows :—Solution 
of perchloride of iron containing much peroxide of iron “won’t keep ;” it soon 
becomes muddy from deposition of the peroxide. If it contains only a small 
amount of peroxide, it is persistent; but on being added to a solution of any 
one of many substances, as in making up a bottle of medicine, the peroxide is 
then deposited, and makes turbid what should be a transparent mixture. 
Manufacturing and dispensing chemists have, in fact, learned by experience 
that to make things work smoothly aqueous solution of perchloride of iron must 
always contain excess of hydrochloric acid. In this way those who supply the 
remedial agent in question remove the fault which is an inconvenience to them. 
But how about those who swallow this medicine? What do medical men, those 
who prescribe and know the action of medicines, say concerning a preparation 
whose name is simply perchloride of iron and water, but which contains hydro¬ 
chloric acid? Well, I must confess that some, high in authority, have told me 
that “ whenever it is necessary to administer perchloride of iron a little hydro¬ 
chloric acid will probably do good rather than harm.” If this be so, I would 
say to the manufacturing chemist, “ Make your solution of perchloride of iron as 
you please, only take care that it is always acid.” If not, I would say to pre- 
scriber and dispenser, “ Do not make your own solution of perchloride of iron at 
all, for the solid perchloride is difficult to make or keep dry in small quantities, 
but order it from a manufacturer who will guarantee that it is so made.” I 
believe a maker of chloride of lime, or any other similar worker in chlorine, 
could produce pure solid perchloride of iron in the manner I suggest, namely, 
* This i s the British Pharmacopoeia process, hut is badly described in that work: operators 
must use rather less nitric acid, and 10 to 20 per cent, more hydrochloric acid than there 
ordered, even if the stability of the preparation is the only object desired. 
