NOTES ON THE CHLORIDES OF IRON. 
4 
397 
Practically, also, this is the simplest process, if a pure, crystalline, anhydrous, 
solid chloride be required ; for iron is inexpensive, and can always be had in 
the convenient form of nails, wire, etc. ; and chlorine is easily made by any one 
having a slight acquaintance with chemical manipulation. The two elements 
attack each other even in the cold, but if the iron be made hot, combination 
proceeds with great rapidity, the result being protochloride of iron, if the iron 
be in large and the chlorine in small quantity, or percliloride of iron, otherwise 
known as sesquichloride of iron, if a continuous current of chlorine be supplied. 
On the small scale, the following arrangement of apparatus may be employed :— 
Generate chlorine by gradually heating a mixture of hydrochloric acid and 
binoxide of manganese in a clean Florence flask, dry it by conveying the gas 
through a glass tube to the bottom of a wash-bottle containing strong sulphuric 
acid ; from this bottle let it flow through another glass-tube to the bottom of a 
second Florence flask one-tliird filled with small iron nails, and kept at a heat ap¬ 
proaching redness by a spirit or gas-flame placed beneath. Under these con¬ 
ditions the percliloride of iron sublimes, and adheres to the upper part of the 
flask. If the operation be discontinued when about half or two-thirds of the 
nails have been acted on, the residual iron will be found to be compacted to¬ 
gether by small micaceous crystals of protochloride of iron. The colour of the 
latter is yellowish-white, soon changing to light-brown in the air, while the 
percliloride forms dark-green iridescent scales. The temperature required 
for the volatilization of the protochloride is far higher than that for the per- 
chloride, hence the condensation of the two salts at different parts of the flask, 
a circumstance which enables the operator to separate the one from the other by 
merely cracking off the bottom of the flask on which the iron and protochloride 
rest. This process is a demonstration of the facts that protochloride of iron is 
formed whenever iron and chlorine are brought into contact, and that perchlo- 
ride of iron is produced by the action of chlorine on protocliloride of iron. The 
apparatus is not the best that could be devised if the protochloride only were 
required, but is well suited for the production of percliloride. In the latter case 
it is not necessary to continue the current of chlorine until all the iron has dis¬ 
appeared, for the nails that are furthest from the end of the delivery-tube are 
not so rapidly attacked as those nearer, and hence towards the close of the ope¬ 
ration there is a free space in the neighbourhood of the delivery-tube, and some 
of the chlorine escapes without acting on the iron. This circumstance, how¬ 
ever, ensures the presence of free chlorine in the upper part of the flask, and 
consequently the freedom of the percliloride there from the least trace of proto¬ 
chloride. From half a pound to a pound of pure perchloride of iron can in this 
way be made in a Florence flask. Much larger quantities are produced with 
facility in a similar manner in more capacious vessels. 
Properties of the Chlorides of Iron .—Perchloride of iron is seldom used in the 
anhydrous solid state either by the pharmaceutist, chemist, or medical practi¬ 
tioner ; it is usually at once obtained in a state of solution. Unless, however, 
the characters of the pure substance be studied, especially its behaviour with 
solvents, we cannot form a correct estimate of the efficiency of the processes for 
the preparation of the solutions. I shall, therefore, briefly notice some of the 
properties of the perchloride and also a few of those of the protochloride, as 
some of the processes for the preparation of solutions of the former involve the 
previous preparation of solutions of the latter. 
Properties of the Perchloride .—Anhydrous perchloride of iron absorbs mois¬ 
ture from the air very rapidly. If a few crystals be exposed on paper they be¬ 
come liquid in a few minutes. Once dissolved in water, however, it yields a 
liquid which will probably remain unimpaired for any length of time, for I have 
specimens a year old, containing 40| per cent, of the salt,—similar, in fact, in 
strength to the solution of perchloride of iron of the British Pharmacopoeia,— 
