230 Dr J. Davy on the Action of 



I shall first mention the experiments which I have made with 

 these acids, atmospheric air having been excluded, or nearly so. 

 Sixty drops of each of the three mineral acids were diluted with 

 six ounces of distilled water, a quantity equal exactly to the ca- 

 pacity of the phials employed. In these mixtures, small bars 

 of polished copper were immersed, and the phials were closed 

 with glass stopples, smeared with a composition of wax and oil. 

 After the lapse of sixty-nine day?, viz. from the 25th May to 

 the 3d August, the results were examined, and were found to 

 be the following : 



The dilute sulphuric acid was colourless, had a just percep- 

 tible taste of sulphate of copper, and, on the addition of ammo- 

 nia, acquired a faint blue hue, and the bar of coppr was slight^ 

 ly tarnished with black oxide of copper, not equally over its 

 whole surface, but more in some places than in others. 



The results in the instance of the dilute muriatic acid were 

 very similar; ammonia imparted to it a bluish tint, just percep- 

 tible, and black oxide of copper tarnished the bar in such a 

 manner, as to produce the appearance of successive strata, with 

 intervals between them, where the brightness of the metal was 

 but little impaired. 



The results with the dilute nitric acid were somewhat differ- 

 ent. The acid had acquired a bright blue colour, and the me- 

 tal was covered with a very thin and slightly adhering crust of 

 black oxide, which was more copiously formed about the mid- 

 dle of the bar than at its extremities, and a little aii' was gene- 

 rated, which was probably either azote or nitrous oxide, for it 

 did not produce a red fume on the addition of atmospheric air. 



Without stopping now to reason on these phenomena, I shall 

 proceed to describe another set of experiments, differing chief- 

 ly from the preceding in this circumstance, that the glass-vessels 

 full of the dilute acids, in which the copper bars were innncrsed, 

 were covered only with glass, so as to retard evaporatian, but 

 not prevent the eniiance of' atmospheric air. After an interval 

 of eight months, viz. from the 3d August to the 2d April, the 

 results were examined. 



The sulphuric acid wns found saturated with copper, and the 



