Metals in Persulphate and Perchloride of Iron. 367 



During these experiments I found that silver, tin, lead, an- 

 timony, bismuth, cobalt, nickel, and several other metals were 

 very soluble in neutral persalts of iron, reducing it to the 

 state of a protosalt. In order to repeat these experiments, I 

 prepared some perchloride of iron in the following manner, 

 adding to the boiling solution of the sulphate as much nitric 

 acid as was necessary to peroxidize the iron, then precipitating 

 by ammonia, washing this well with hot water, and dissolving 

 with hydrochloric acid, evaporating nearly to dryness, and 

 adding a quantity of distilled water. The persulphate used 

 was obtained as a dry white powder ; both salts were neutral. 



I was aware that Professor Fuchs had recommended the 

 boiling of a piece of clean copper in perchloride of iron as a 

 means of ascertaining the quantity of iron in an ore of that 

 metal, and also to ascertain the amount of copper in certain 

 copper ores. For iron ores I have found great difficulty in 

 obtaining uniform results, from the great difficulty of knowing 

 the exact period at which the iron is all reduced to the proto 

 state, for the copper put in continues to dissolve until the 

 chloride is all converted into a subchloride; this result is 

 effected, however, much more rapidly when the iron salt is 

 neutral than when it contains free acid, a condition specially 

 recommended by Fuchs. 



The most uniform results are obtained by allowing the 

 copper to remain until the solution becomes colourless ; on 

 diluting with cold water, the whole of the copper is precipi- 

 tated as a white powder ; the clear solution, if the process is 

 completed, will contain no copper, when there will be two 

 equivalents of copper dissolved from the metal for every equi- 

 valent of peroxide of iron formerly in the solution. It occa- 

 sionally happens, however, when neutral salts of iron are used, 

 that the copper becomes encrusted with a white deposit, upon 

 which crystals of the subchloride of copper collect, and thus 

 protect it from further action ; this is prevented by boiling, 

 or taking out the copper, removing the crust, washing it, and 

 putting it into the solution again, when the action goes on as 

 before. When the persulphate of iron is used for this pur- 

 pose instead of perchloride no subsalt is formed, and the 

 result is uniform, one equivalent of copper being dissolved 

 for every equivalent of peroxide of iron present in the solu- 

 tion. 



I may mention one especial application of the solubility of 

 copper in perchloride of iron, namely, the dissolving copper 

 from the surface of silver, such as copper that has been used 

 as a mould in which silver has been deposited ; when this so- 

 lution becomes saturated with copper, a little ammonia added 



