546 
conceuti-alion of t!te acid, llie temperatnre and the concentration of 
tlie Products of the reaction accumulating in tiie solution. 
MtT,LON (Compt. rend. 1842, 14, 904) and Veley (Pliil. Trans. 
1891 A, 182, 279) have shown tSiat metals like copper, silver, 
mercurj and bismnth have no action on cold dilnte nitric acid 
unless a tracé of nitrous acid is present. Tlie nitrous acid inay be 
present in the nitric acid as an impnritj ; it may be formed by the 
incipient decomposition of nitric acid when it is warmed. 
According to Veley, rherefore, the dissolution of copper in nitric 
acid proceeds : Cu + 3 HNO, = Cu (NO,), + HNO, + H,0, is a 
resuitant of a series of consecutive reactions : Cu -j- 4 HNO, = 
Cu (NOJ, + 2 H,0 + 2 NO ; followed by Cu (NO,), + 2 HNO, = 
Cu (NO,), + 2 HNO,. 
The sinall tracé of nitrous acid thus acts as a catalytic agent; 
nitrous acid is continuously produced and continuously decomposed 
according to the following equiübriurn : 
\ 
3 HNO, HNO, + 2 NO + H,0 
Similar results have been obtained by Ray (Trans. Chem. Soc. 1911, 
99, 1012) in the case of inercury and by Stansbie (J. Soc. Chem. 
Ind. 1913, 32, 311) in the case of silver. 
Now Milj.on (loc. cit.) and Vei.by (loc. cit.) have pointed out that 
the presence of ferrous sulphate, “which reraoves 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 207 o nitric 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 sectiona! area were 
placed into test tubes and covered with an excess of 20“ , nitric 
acid. The mean temperatnre of the experirnents was 18° and the 
tubes containing equal volumes of nitric acid and equal weights of 
copper wire were kept at rest. Weiglied qua.ntities of the solid 
substances used were added at the beginning of the experirnents. 
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- 
