Mineral Acids on Copper. 231 



bar covered with a thin crust of black oxide of copper, and nni- 

 formly covered, with the exception of the upper part of it, 

 which was ahiiost free from stain to the extent of about two 

 hnes, which was more corroded tlian the surface in general, and 

 whicli, from evaporation, rose above the fluid. The nitric acid, 

 too, was foimd saturated, and the top of the bar of copper pro- 

 jecting a very httle above the surface of the solution, but it was 

 still moist. There was a pretty considerable deposition of pro- 

 toxide of copper on the bar, with a little subnitrate of copper, 

 and a very minute quantity of copper in its metallic state. The 

 subnitrate was found chiefly at the two extremities of the bar ; 

 the protoxide was very generally deposited, whilst the metallic 

 copper was almost entirely confined to one side, and to a small 

 space towards the upper end of the bar. The deposition being 

 crystallized, and the colours bright and distinct, the appearance 

 it made was brilliant, especially when placed in the sunshine, 

 and resembling, in miniature, native specimens of the same 

 kind. 



The results in the instance of the muriatic acid were very si- 

 milar; submuriate, protoxide, and metallic copper, were de- 

 posited. The submuriate was very abundant, and collected 

 chiefly about the lower part of the bar, where it had formed 

 crystallized plates, not unlike what is seen in the native speci- 

 mens of this mineral from Peru. The protoxide was in a smal- 

 ler quantity than in the preceding experiment, as well as the 

 metallic copper, and their crystalline form was less distinct. 



I have made a third set of experiments, with this difference 

 only in conducting them, that the bar of copper, in each in- 

 stance, was only half immersed in the dilute acid, and that at- 

 mospheric air had free access, in consequence of which, evapo- 

 ration of the fluid went on pretty rapidly, and it was necessary 

 every now and then to add water, to prevent desiccation. I do 

 not consider it necessary to describe the results minutely; 

 they were much the same as those obtained when atmospheric 

 air was admitted, and evaporation partially prevented, excepting 

 in the case of the sulphuric acid, in which, on this occasion, the 

 charges were analogous to those exhibited with the other two 

 axiids; thus far, at least, that protoxide of copper was deposited, 

 and a slight trace of metallic copper. 



