526 Dr. Andrews's Report on the Heat of Combination. 



Solution of Zinc in Nitric Acid, 



I. II. III. IV. 



Temperature of air 4'5 6*2 8*0 5*8 



Increment found . . 2-66 2-78 2-83 2*7 1 



Increment corrected 2-65 2*77 2-82 2-71 



Weight of zinc .... 0-587 grm. 0*600 grm. 0-615 grm. O-eO* grm. 

 Weight of water . . 294-8 284-4 289'3 294-6 



Value of acid 7-4 6*9 QS 6*6 



Value of vessels 14-3 14-3 14-3 14-3 



Heat of combination 1429 1411 1422 1420 



Hence we have for the heat disengaged during the solution in 

 nitric acid of — 



1 grm. zinc 1420 



1 equiv. zinc 5857 



Solution of Copper in Nitric Acid. 



I. II. III. IV. 



Temperature of air. . 8*9 6-8 7*8 8°5 



Increment found ^i*56 2-58 2-58 2-57 



Increment corrected . . 2*55 2*56 2-57 2-56 

 Weight of copper .. ..1-202 grm. 1*204 grm. 1-206 grm. 1-21 3 grm. 



Weight of water . . 274-2 273*2 273*3 275*4 



Value of acid 14*5 16*8 15*6 15-5 



Value of vessels .. 16-8 16-8 16*8 16-8 



Heat of combination 648 652 651 650 



We have therefore for the heat disengaged during the solution 

 in nitric acid of — 



1 grm. copper 650 



1 equiv. copper 2578 



I made several attempts to determine the amount of heat disen- 

 gaged in the solution of iron in nitric acid, but although acids of 

 different strengths were employed, I was unable to obtain satisfactory 

 results, as the iron always assumed the passive state before a suffi- 

 cient quantity was dissolved to raise the temperature of the water 

 in the calorimeter through 1°. Silver, bismuth and other metals 

 were also tried, but the solution did not proceed with sufficient 

 energy. 



The numbers 5857 and 2578 obtained above, are very nearly in 

 the same ratio as 5366 and 2394, which, according to my experiments 

 (and their results differ little from those of Dulong), express the 

 quantities of heat set free by the combustion of zinc and copper in 

 oxygen gas. This shows clearly that the oxidation of the metals is 

 the principal cause of the heat produced during their solution in 

 nitric acid. Other causes of thermal change however exist, which 

 must exercise a considerable influence. Such are the combinations 

 of the oxide with the nitric acid, the separation of the elements of 

 a portion of the nitric acid during the solution, and the condensation 

 of the oxygen gas during the combustion. From these and other 



