Conditions of Chemical Change, 183 



In the course of the investigations conducted by Burch and 

 myself on the E.M.F. of certain cells containing nitric acid, 

 it was continually found that if the containing vesssel was not 

 clean, if the metallic strips were touched with the fingers, or 

 if the strips were not thoroughly cleansed, the E.M.F. of the 

 cell rose to its maximum at once. It is quite clear, therefore, 

 that a trace of the nitrous compound could be formed in 

 numerous ways, and, when once formed, would tend to increase 

 in the presence of the metal. The recent investigations of 

 Sabatier and Sanderens* have shown that finely divided 

 copper readily absorbs nitrogen peroxide at ordinary tempe- 

 ratures to produce a nitro-copper of composition Cu 2 N0 2 , 

 upon which water reacts with violence to give a solution 

 of copper nitrate and nitrite, nitric-oxide gas being evolved. 



Though it is not wholly safe to argue from the results of 

 experiments conducted under one set of conditions to those 

 conducted under another, yet it is remarkable that the pro- 

 ducts of the reaction of copper with diluted nitric acid are in 

 the main identical with those of water with the nitro-copper. 

 The conclusion is not, therefore, wholly improbable that the 

 nitrogen peroxide present in the nitric acid combines with 

 the copper to form intermediately the nitro-copper, which in 

 its turn is decomposed by the water to re-form the nitrous 

 compound. The researches of Freer and Higley t have 

 further shown that in the case of concentrated acids the main 

 product of the reaction of metallic copper is nitrogen peroxide. 



It is also remarkable that metallic lead dissolves very rapidly 

 in the liquid obtained by the addition of nitrogen peroxide to 

 water J, even though of a less degree of acidity than other 

 mixtures of nitric acid and the nitrous compound, though 

 here again it is not wholly safe to argue from the results 

 obtained in the case of one metal to those of another. At 

 present I am engaged upon this point for metals other than 

 lead. If, then, the formation of nitrogen peroxide be accom- 

 plished, then not only will nitric oxide result, but also the 

 more deoxidized products such as nitrous oxide and nitrogen 

 will be produced from subsidiary reactions between the nitric 

 acid and the metallic nitrates. The formation, therefore, 

 of all the products in the case of the metals mercury, copper, 

 silver, and bismuth can readily be explained without recourse 

 to the convenient hypothesis, nascent hydrogen. But at 

 present there is no satisfactory explanation of the formation 

 of ammonia and hydroxylamine, and this mainly for the 



* Bull. Soc. Chim. [3] ix. pp. 669-674. 

 t Amer. Chem. Journ. 1893, p. 71. 

 % Journ. Soc. Chem. Indust. 1891, 

 02 



