Book II. 
Division II 
How chan 
ged inte 
sulphat. 
SALTS OF 
for some time, or by pouring into it nitric acid, and ap 
plying heat *. 
This salt has a red colour. It does not afford crystals; 
and when evaporated to dryness; soon attracts moisture, 
and becomes again liquid. It is exceedingly soluble in 
water, and also in alcohol. By this last liquid it may 
be separated from the sulphat of iron, with which it is 
always mixed in the vitriol of commerce. When ex 
posed to the air, it gradually deposites red oxide, or ra 
ther oxy sulphat with excess of base. 
A great number of substances have the property of 
depriving this salt of its excess of oxygen, and of con 
verting it into sulphat of iron. This is the case 
with iron. When the solution of oxy-sulphat is mix 
ed with iron-filings, and kept for some time in a 
well-covered vessel, part of the iron is dissolved by 
abstracting the second dose of oxygen from the oxide, 
and the whole is converted into sulphat. The same 
change is produced by tin, and probably also by all 
the salts of tin which contain that metal combined 
with a minimum of oxygen. Sulphurated hydrogen 
produces that change instantaneously when made to 
pass through a solution of oxy-sulphat *. That gas has 
the property of reducing the oxides of iron to a mini 
mum of oxygen ; but it does not bring them to thé me 
tallic state. Hence the reason that it does not preci 
pitate iron from its solution in acids. 
On the other hand, all those bodies which part with 
oxygen very readily, convert the sulphat of iron into 
* During this change a quantity of ammonia is also formed. Hence 
not only the nitric acid but some water also is decomposed.—See Davy's 
Researches, p. 157. 
Proust, Ann. de Cbim. xxii. 23.