138 
ON CHLORIDE OF IRON AND SODIUM, ETC. 
may be stated as a general truth, to which there may not be an 
exception, that there cannot be formed a neutral, simple and 
soluble salt of the sesquioxide of iron. The perchloride of iron, 
the nitrate and sulphate of the peroxide, are soluble, and acid and 
the vegetable acids form similar salts with the sesquioxide of iron. 
Therefore the excess of acid of any of these soluble salts may be 
neutralized with any of the alkalies, potassa, soda or ammonia, 
and form double salts. But in the preparation of these double salts, 
it is very important first to form the salt of iron by saturating the 
acid with sesquioxide of iron, and neutralizing the excess of acid 
with an alkali, because almost all the acids have a less affinity 
for the metals than for the alkalies, and if the affinity be satisfied 
by the union of the acid and alkali, and the alkali have an affinity 
for only one equivalent of the acid, as is the case in chloride of 
sodium and chloride of ammonium, it is impossible to form double 
salts by adding any oxide of iron or solution of iron in the same 
acid to either of these salts. But if the alkali have a strong 
affinity for more than one equivalent of the acid, then the excess 
of the acid combined with the alkali may be neutralized, as in the 
preparations of tartrate of potassa and iron, tartrate of potassa and 
antimony, and tartrate of potassa and soda. 
Thus tracing the analogy which seems to be almost parallel in 
these preparations, I have chemically combined chloride of iron 
with potassium and ammonium separately, and found two distinct 
double salts. But of these double salts, chloride of iron and sodium 
seems to be the most important. I have repeatedly tried in a 
variety of ways to form this double salt, by mixing and evapora- 
ting at different temperatures solutions separately formed of 
perchloride of iron and chloride of sodium, but the result has 
been uniformly crystallized chloride of sodium in a solution of 
perchloride of iron. I have separated the former from the latter 
almost pure, by simply washing it with water. These experiments 
carefully performed, convinced me that I could only prepare the 
double chloride of iron and sodium by one process, viz : preparing 
the perchloride of iron and neutralizing the excess of acid with 
caustic or carbonated soda. I prefer the following formula : 
Take of Commercial Carbonate of Iron, 8 ounces troy. 
" Hydrochloric Acid, pure, sp. gr. 1.18, 24 fluid ounces. 
" Bicarbonate of Soda, 18 ounces troy. 
" Boiling water, - - 72 fluid ounces. 
