184 Mr. V. H. Veley on Chemical Change. 



reason that the reactions between nitric oxide and metallic 

 nitrates have hitherto received but little attention. 



The reactions of metals with sulphuric acid have not been 

 the subject of many investigations, partly, no doubt, from 

 their assumed simplicity. Even at present there is no exact 

 knowledge as to the nature of the intermediate substance 

 formed from the sulphuric acid, which enables the metal to 

 dissolve and to continue dissolving ; probably it is some pro- 

 duct of electrolysis, for it has been shown that pure zinc 

 dissolves in diluted sulphuric acid through which an electric 

 current has been passed, though no reaction ensued between 

 the same samples of zinc and sulphuric acid previous to the 

 passage of the current. Yet, whatever this substance may 

 be, if the metal dissolves in the dilute acid, there are always 

 formed traces, however small, of products other than hydrogen, 

 and especially of hydrogen sulphide, while cadmium (which 

 in many other respects resembles zinc) gives such reduction- 

 products that the liquid turns milky with formation of 

 sulphur. 



The reaction of copper and allied metals with concentrated 

 sulphuric acid is generally represented as taking place in two 

 successive stages, namely, first the direct replacement of the 

 hydrogen by the metal, and, secondly, the reduction of the 

 sulphuric acid by the nascent hydrogen, thus : — 



(1) Cu + H a S0 4 = CuS0 4 + H 2 ; 



(2) H 2 S0 4 + H 2 = 2H 2 + S0 2 . 



But here, again, there seems to be but little necessity for 

 the hypothesis of nascent hydrogen, for the reaction only 

 ensues with more concentrated acid, in which there is a 

 greater tendency towards a decomposition of the acid into the 

 trioxide and water, and the metallic copper may reduce the 

 former with formation of cupric oxide and sulphur dioxide. 

 Or, if the solution of the metal, as that of zinc in sulphuric 

 acid, is dependent upon some product of electrolysis, the 

 metal per se may directly reduce this. Though neither of 

 these views is as yet confirmed by experimental investigation, 

 yet both appear to be more probable than that of nascent 

 hydrogen. 



Investigations upon the conditions of formation and func- 

 tion of these intermediate compounds are greatly wanted, 

 especially as the chemical changes between metals and acids 

 resemble others discussed above, in that they pass through 

 the same successive phases. 



The University Museum, Oxford. 



