On the Decomposition of neutral Sulphate of Iron, 131 
tion, which may be determined by the quantity of the salt pre- 
cipitated. The results were as follows : dissolved in 
100 parts of water, 0*309 precipitated. Opacity com- 
menced at 203°F. 
200 — 
— 0-S58 
— 
— — 158 
400 — 
— 0-V49 
— 
— — 137 
800 — 
— 0-806 
— 
— — 122 
1000 — 
— 0-912 
— 
— — 117. 
If 1 part of the sulphate of iron was dissolved in 10*000 
parts of water, the solution became opake even at the temper- 
ature of about 63° F. which was that of the water employed ; 
but if it was afterwards heated to boiling, not a trace of iron 
could be detected in the solution filtered from the precipitate 
either by ammonia or by tincture of galls. The above quantities 
are mere approximations to accuracy, as in the first place, 
during the boiling of the solution, more or less water is eva- 
porated, by which the degree of dilution is altered ; 2ndly, 
the water which is condensed in the upper part of the tube 
again falling down, causes a momentary increased dilution, 
and consequently an increased quantity of the precipitate; 
and Srdly, the boiling point is heightened the greater the 
quantity of salt of iron dissolved in the water. Nevertheless 
the result of the experiments is sufficiently accurate to al- 
low of our establishing the following law with respect to the 
relative quantities of the peroxide of iron remaining in solu- 
tion after boiling : With a 200 fold and greater dilution^ the 
quantities of the peroxide of iron remaining in solution are 
in inverse ratio to the dilution. Indeed if these quantities are 
calculated acording to the above-mentioned proportions, we 
find approximatively that. 
With a 200-fold dilution, \ of the peroxide of iron re- 
— 400 — i — mains dissolved. 
•— 800 — I — 
— 1000 -- _i_ — 
This progression, however, is not generally exact, for in- 
stance by a 100-fold dilution |ds of the iron should remain 
dissolved. The law therefore is approximative only for the 
central members. 
If a solution of the neutral sulphate of the peroxide of iron 
is mixed with a solution of the neutral sulphate of potash, the 
same basic salt is precipitated without any part of the potash 
entering into the combination. The properties of the solu- 
tion of sulphate of iron now described may be employed to 
separate the peroxide of iron from some salts. The neutral 
sulphates of manganese, nickel and cobalt have no acid re- 
action upon litmus paper like the neutral sulphate of the per- 
K2 
