370 Mr. J. Napier on the Solubility of the Metals, §c. 



Platinum in persulphate and perchloride of iron produced 

 no change, neither lost anything in weight. 



Gold boiled for a long time in perchloride of iron in two 

 experiments lost 0*2 and 0*3 of a grain. In both these in- 

 stances beautiful crimson-red crystals, in perfect octahedrons, 

 were obtained, adhering to the metal and also to the con- 

 taining vessel. I did not try whether they contained any 

 gold. These results were only obtained twice in six different 

 trials ; they were procured with iron prepared at different 

 times. Platinum was always tried at the same time with the 

 gold, and when there was no gold dissolved I never obtained 

 any crystals. 



I need hardly mention that both zinc and iron, when put 

 into the persalts of iron, first reduce the persalt to the pro- 

 tosalt, which fully accounts for the great consumption of iron 

 for the small quantity of copper obtained in these waste waters 

 of mines, and not, as was generally supposed, from the exist- 

 ence of free acid ; the copper is never all precipitated from 

 the water so long as persalts of iron exist in the solution. 

 The presence of persalts of iron also prevents the deposition of 

 the copper by a galvanic current ; the proportionate quantity 

 of persalts of iron necessary to resist completely the deposition 

 of copper was not ascertained. 



In no one case did I find any double salt formed between 

 the iron and metal dissolved in it, but when the solution con- 

 taining them was evaporated the salts of the two metals cry- 

 stallized separately. 



In all cases where the process is conducted cold the solu- 

 tion of the metal takes place at the bottom of the vessel and 

 progresses upwards; this is beautifully exhibited when a tall 

 glass is used with a solution of perchloride of iron, and a slip 

 of copper reaching to the bottom ; the solution first becomes 

 green at the lower part, and this advances slowly upwards till 

 it reaches the top, but before the change of colour reaches the 

 top the bottom has become colourless from the formation of 

 subchloride. 



I may observe that the whole of these remarks are only the 

 prominent features noted down as they occurred, without any 

 idea of bringing them before the Society in this unfinished 

 state ; but having no hope of obtaining leisure for making 

 further investigations, I have given them as they are, thinking 

 that perhaps some one, having more time and ability, would 

 repeat the experiments and produce something more definite. 



