the Action of Copp er-Zinc Alloys on Nitric Acid. 235 



Two results stand out prominently from the above figures. 



1. The chemical action of the alloys is very different from 

 the chemical action of the corresponding mixtures of filings. 

 It will be seen by a glance at Table I. that the alloys give 

 much more nitrous acid and very much less ammonia than 

 the corresponding mixtures. In fact, two of these alloys give 

 practically no ammonia. 



2. On comparing the figures for the mixtures of solutions 

 in Table II. with the solutions of mixed metals in Table I., it 

 will be seen that there is a notable difference both in regard 

 to the nitrous acid and to the ammonia. This might be 

 anticipated from the fact that, when the copper and zinc 

 filings are mixed together, they form what has been described 

 under the name of the iC copper-zinc couple." The two 

 metals in juxtaposition and touching at a multitude of points 

 while surrounded by acid set up a more vigorous action, with 

 different chemical results and no doubt a different evolution 

 of heat *. It is probably this action which causes Dr. Grains 

 numbers for heat of mixtures to lie generally below the 

 theoretical straight line joining zinc and copper in the 

 diagram accompanying the report of the Committee. 



The chemical objection therefore is well founded. It is a 

 very serious one ; but is it necessarily fatal ? 



Would it not be possible to take some particular alloy, 

 determine the products of its action on nitric acid, and their 

 relative proportions, and then determine the number of 

 calories which would be produced theoretically in the 

 reaction ? If they agree closely with the number of calories 

 found by Dr. Gralt and Mr. Baker, there is no room for 

 supposing that the amount of heat evolved in making the 

 alloy is to be determined by this method. If, however, the 

 two calculations differ, there is a residual phenomenon to be 

 explained. 



But here we encounter two difficulties. 



1. Though we may know the ultimate composition of all 

 the specimens of copper-zinc alloys experimented upon, pro- 

 bably not one of them is a truly definite compound. Bach of 

 them may consist of two or more alloys with some uncom- 

 bined zinc or copper, as the case may be. A microscopical 

 examination is generally sufficient to show that each is more 

 or less heterogeneous in its character. Sir W. Roberts- 

 Austen's table of the freezing-points of alloys of copper and 

 zinc also indicates the mixed nature of almost every specimen 



* See Journal Chem. Soc, April 1878, where the experiments of Prof. 

 Thorpe and of Gladstone and Tribe on the production of nitrite arid 

 ammonia by means of the copper-zinc couple are described. 



