1889.] Reaction between Copper and Nitric Add. 



221 



forming silver nitrite, nitric oxide, and water,- the nitric oxide 

 thus formed reducing hydric nitrate, and forming more nitrous 

 acid. Thus the action gets quicker and quicker. The point still 

 remaining to be explained is, then, how the first trace of nitrous 

 acid is formed." My experiments, mutatis mutandis, are quite 

 in accord with these observations. To test the matter further, the 

 temperature of the same sample of acid was raised to 30° C, other 

 experiments having shown that the amount of copper dissolved off 

 per unit area is doubled for every 4° C. No gas was evolved for 4' 

 after the introduction of the copper sphere, it was then taken out, 

 and again introduced, and again no gas was evolved for 4'. The loss 

 in weight after the 8' insertion was only 0*0025 gram, whereas it 

 was calculated that the amount dissolved off during the interval of 

 time, supposing the urea to have been absent, would Lave been 

 0*11 gram. 



Into the same liquid a further quantity of 2 grams urea dissolved in 

 2 c.c. of water was added ; the acid was heated to 28 — 28*2° C, no gas 

 was evolved for 18' ; then as the supply of carbonic acid accidentally 

 failed, the evolution of gas from the copper started ; the loss of 

 weight observed was 0"0015 gram, a quantity which might well have 

 been dissolved off during the interval of time which elapsed between 

 the commencement of the reaction and the removal of the sphere 

 from the acid. During the experiment it was interesting to observe 

 from time to time the formation of a bubble of gas on the metallic 

 surface, which was brushed off: by the rotation of the glass dish 

 or the stream of carbonic acid, and consequently any further reaction 

 stopped. 



As a further confirmation another sample of acid was made up, 

 containing' a slightly greater proportion of free acid, viz., 28'2 per 

 cent., sp. gr. \% = 1*1723 ; a larger sphere was taken presenting an 

 area of 322*38 sq. mm. 



The acid was heated to 27° C. ; and 2 grams urea dissolved in 

 2 c.c. w T ater were added, No gas was evolved for 50', and the loss of 

 weight observed was only 0*0015 gram. 



Several other similar experiments have been made with similar 

 results, which, however, it is not considered necessary to quote. 



The conclusions which I venture to think may fairly be drawn 

 from the observations herein described are : — 



(1.) The view of Professor Armstrong is corroborated that the 

 primary product of the reduction of nitric acid by copper is nitrous 

 acid ; the latter is formed immediately after any chemical change 

 has taken place. 



(ii.) If this initial formation of nitrous acid be prevented by suit- 

 able means copper by itself will not dissoloe in dilute nitric acid by 

 itself. 



