368 Mr. J. Napier on the Solubility of the 



precipitates the iron as a peroxide and combines with the 

 copper, forming a soluble double chloride, which may be im- 

 mediately separated by filtration and the precipitate washed, 

 the peroxide of iron again dissolved in hydrochloric acid is 

 fitted for a renewal of the same operation. I may here men- 

 tion, that if, previous to adding the ammonia, there be a little 

 perchloride of iron put into the mixture of subchloride of cop- 

 per and protochloride of iron, an immediate change is effected, 

 the colour of the solution becomes green, and on adding am- 

 monia to this, both copper and iron are precipitated. 



Persulphate of iron cannot be used for the purpose of dis- 

 solving copper from silver, both from the easy solubility of 

 silver in solutions of this salt, and also from a peculiar de- 

 structive action which it has upon alloyed silver. Standard 

 silver is completely destroyed. I have used thin sheets, 

 weighing from 60 to 70 grains, and when only 4 grains were 

 apparently dissolved the remainder had been so much affected 

 that it crumbled between the fingers like a dried leaf. 



When silver is put into a solution of persulphate of iron an 

 immediate action takes place, a yellowish cloud begins to form 

 in the solution; if heated the action is much more rapid, a 

 yellow oxide of iron forming upon the sides of the vessel, and 

 there is also a brown precipitate deposited ; the iron in the 

 solution is converted into the proto state, shining particles of 

 metallic silver float through the solution, and sulphate of sil- 

 ver crystallizes on the vessel, but in no case did I find an 

 equivalent of silver for the equivalent of peroxide of iron ; by 

 slow evaporation the solution yielded crystals of protosulphate 

 of iron and sulphate of silver. 



Tin is very easily dissolved in both the persulphate and per- 

 chloride of iron, completely reducing them to the proto state. 

 When the solution is cold this is effected in about an hour; 

 when hot, in a few minutes; the iron is reduced to the proto 

 state when only half an equivalent of tin is dissolved for every 

 equivalent of peroxide ; my first impression was, that the first 

 atoms of protosalt of tin formed reduced a corresponding atom 

 of peroxide of iron, and was converted into a persalt; but sa- 

 turating with ammonia, and adding it in great excess, the pre- 

 cipitated oxide of tin was not redissolved, and had every other 

 character of a protosalt. Whether this was owing to the for- 

 mation of a bisulphate or bichloride of' tin, I did not ascertain ; 

 but by boiling or long standing there is an equivalent of tin 

 dissolved for every atom of perchloride of iron, but I did not 

 obtain the same result in the persulphate. 



Cadmium is very soluble in persalts of iron ; in the persul- 

 phate an equivalent of cadmium is dissolved for the equivalent 



