On the Decompositio7i of neutral Sulphate qf 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. Opncity com- 



menced at 203°F. 

 200 — — 0-558 — _ _ 158 



400 — — 0*749 — — — 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 dilation 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 Srdl}', 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 2Q0-fold and greater dilution, the 

 quantities of the peroxide qf 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 — -1- — 



This progression, however, is not generally exact, for in- 

 stance by a 100-fold dilution fds 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 



