the Action of Copper-Zinc Alloys on Nitric Acid. 233 



of copper, a more rapid and irregular decrease takes place till 

 we arrive at that containing 38 per cent, of copper. From this 

 point, or rather from copper 38" 38 per cent., there is a gradual 

 and fairly regular descent to the amount of heat evolved by- 

 pure copper. 



The somewhat similar series of experiments conducted b}* 

 Mr. Baker (Proc. Chem. Soc, Sept. 1899) is exhibited in the 

 lower part of the same diagram, the resulting calories being 

 plotted in the same way from 1399 down to 579. There is a 

 fairly close resemblance between the two series, except that 

 in the latter the most rapid decrease of heat does not take 

 place till at about 54 per cent, of copper. 



Through the kindness of Lord Kelvin I obtained three 

 specimens of the alloys employed in Dr. Gait's experiments ; 

 the first containing 20"5 per cent, of copper and 79*5 percent, 

 of zinc, the second 38"38 per cent, of copper and 61*62 per 

 cent, of zinc, and the third 49'1 per cent, of copper and 509 

 per cent, of zinc. The first and second specimens are not far 

 from those which show the greatest divergence in opposite 

 directions in the amount of heat evolved ; in the third the two 

 metals are very nearly in atomic proportions. In dissolving 

 these in nitric acid I followed essentially the process employed 

 by Dr. Gait, with the precautions mentioned by him. 



As is well known, the reaction between nitric acid and 

 these metals or alloys is very complicated, producing nitric 

 and nitrous oxides and nitrogen, evolved as gases but which may 

 be partially or wholly absorbed ; while the liquid is found to 

 contain, in addition to the undecomposed acid, nitrous acid, 

 and nitrates or nitrites of the metals, and in some cases 

 ammonium salts. 



The gases have already been the subject of examination by 

 several experimenters. Messrs. Acworth and Armstrong 

 (Journ. Chem. Soc. 1877, p. 54) showed that in the case of 

 copper in nitric acid the gas obtained is almost entirely nitric 

 oxide, while in the case of zinc it is mainly a mixture of 

 nitric and nitrous oxides in very nearly equal proportions, 

 In an experiment with brass they obtained practically the 

 same result as with copper alone. As far then as the gases 

 are concerned, the chemical action of copper and of zinc on 

 nitric acid is not the same ; and the insignificant quantity of 

 the nitrous oxide when brass is dissolved suggests an essential 

 difference in the reaction between the alloy and the mixed 

 metals. 



It did not seem necessary to repeat the experiments ot 

 Armstrong, especially as the permanent gases evolved in 

 Dr. Gait's experiments were small in quantity, at any rate in 

 the case of the yellow alloy. My attention has therefore been 



