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concentration of the acid, the temperature and the concentration of 
the products of the reaction accumulating in the solution. 
Mitton (Compt. rend. 1842, 14, 904) and Verey (Phil. Trans. 
1891 A, 182, 279) have shown that metals like copper, silver, 
mercury and bismuth have no action on cold dilute nitric acid 
unless a trace of nitrous acid is present. The nitrous acid may be 
present in the nitric acid as an impurity; it may be formed by the 
incipient decomposition of nitric acid when it is warmed. 
According to Ve.ry, therefore, the dissolution of copper in nitric 
acid proceeding: Cu + 3 HNO, = Cu (NO), + HNO, + HO, is a 
resultant of a series of consecutive reactions: Cu + 4 HNO, = 
Cu (NO), + 2 H,O + 2 NO; followed by Cu(NO,), + 2 HNO, = 
Cu (NO,), + 2 HNO,. 
The small trace of nitrous acid thus acts as a catalytic agent; 
nitrous acid is continuously produced and continuously decomposed 
according to the following equilibrium: 
3 HNO, = HNO, + 2 NO + H,0. 
Similar results have been obtained by Ray (Trans. Chem. Soe. 1911, 
99, 1012) in the case of mercury and by Sranspiz (J. Soe. Chem. 
Ind. 1913, 32, 311) in the case of silver. 
Now Mirror (loc. cit.) and Verer (loc. cit.) have pointed out that 
the presence of ferrous sulphate, “which removes the nitrous acid 
as fast as it might be formed” serves to prevent the chemical change 
between nitric acid and the metals. 
But I have observed that ferrous sulphate exerts an accelerating 
influence on the complete dissolution of copper in 20°/, nitrie acid 
at 18°. This result being different from those of previous investigators, 
I thought it worth while to observe the effect of both ferrous and 
ferric salts and various other substances on the complete dissolution 
of copper in excess of 20°/, nitric acid. 
Equal lengths of copper wire of uniform sectional area were 
placed into test tubes and covered with an excess of 20° , nitric 
acid. The mean temperature of the experiments was 18° and the 
tubes containing equal volumes of nitrie acid and equal weights of 
copper wire were kept at rest. Weighed quantities of the solid 
substances used were added at the beginning of the experiments. 
The whole of the copper wire dissolved in about 30 minutes and 
the exact time of dissolution was noted. In order to get exactly 
comparable results one test tube was always set apart for a blank 
parallel experiment. : 
It has been found that the following substances exert an accelera- 
