1889.] Reaction between Copper and Nitric Acid. 



217 



carbonic acid was also passed through the liquid to ensure its perfect 

 agitation, and thus to remove the products of the reaction from the 

 immediate vicinity of the metal. 



The nitric acid was made up in considerable quantity at a time by 

 diluting acid of sp. gr. 1*41 with a suitable proportion of water ; the 

 specific gravity of the diluted acid was taken by means of a very 

 delicate pyknometer of the form devised by Sprengel; and the amount 

 of free acid determined in the same portion by the ordinary process 

 of acidimetry. The weight of the copper sphere, as also its diameter, 

 was determined before and after each experiment, which lasted for one 

 hour ; from the diameters the mean area of metallic surface exposed 

 was calculated ; thus the amount dissolved off per unit area could be 

 directly determined. 



In some earlier experiments made with a view of ascertaining this 

 amount, it was noticed that when the sphere of copper was introduced 

 into the acid the evolution of gas did not commence at once, but if, 

 other conditions remaining the same, the sphere was introduced into 

 the acid containing in small quantities the products of the reaction 

 of a former experiment, the evolution of gas commenced immediately. 

 Further, the amount of copper dissolved per unit area was less in the 

 first than in the succeeding experiments, after the products of the 

 change had been allowed to accumulate in the acid. This will be 

 rendered more evident by the figures given in the table below, the 

 first two columns of which contain the weights of two copper spheres 

 A and B (placed alternately in the acid) before and after each experi- 

 ment, the third the differences between these two numbers, the fourth 

 the mean area in square millimetres, and the fifth the amounts 

 dissolved off per unit area expressed as decimilligrams per square 

 millimetre surface, written for the sake of brevity M/A. In this and 

 all succeeding experiments a long-range thermometer was used. 



Table I. 



Sp. gr. of Acid at 19° compared with Water at the same Temperature 

 = 1*1699. • Percentage of free Nitric Acid = 27'53. Tempera- 

 ture 25°. 



Weight at com- 

 mencement. 



Weight at 

 conclusion. 



Loss. 



Mean 



area. 



Value of 



A 



4-4153 (A) 



4-0768 



-3385 



291 



95 



11-60 



4-5823 (B) 



4-2' >49 



-3774 



300 



05 



12-38 



4-0768 (A) 



3 -7378 



0-338 



275 



83 



12-25 



4-2049 (B) 



3 -8465 



0-3584 



283 



•16 



12 65 



3-7378 (A) 



3-4166 



3125 



261 



•23 



12-37 



3-8465 (B) 



3-5268 



-3197 



266 



•78 



12-10 



3-4166 (A) 



3 -1188 



0-2975 



246 



•52 



12-07 



