144 Proceedings of Boy al Society of Edinburgh. [sess. 
as those used in the experiments described, and for which the value 
76*6 heat units Centigrade was obtained as the heat of formation of 
one gramme of the alloy. Having obtained this result, the experi- 
ments were repeated, a new alloy and a new mixture of the same 
metals in proportions very different from the relative combining 
weights referred to beiilg used. The proportions were 70 per cent, 
copper and 30 per cent, zinc, and the specimens were again sup- 
plied by Mr M‘Phail. Some of the latest results, obtained on 6th 
February last, are given in the tabular statement below. 
Heat of Solution of *5 gramme (*35 gramme Copper mixed ivith 
T5 gramme Zinc) of the Mixed Metals and of *5 gramme of 
the Alloy. 
Mixture. 
Alloy. 
Temperature of the Acid before and 
Temperature of the Acid before and 
after Solution. 
after Solution. 
Before. 
After. 
Difference. ; 
Before. 
After. 
Difference. 
C.° 
C.° 
C.° 
C.° 
C.° 
C.° 
9'45 
16-90 
7 '45 
10-75 
17-90 
7-15 
9-90 
17-38 
7-48 
10-85 
17-99 
7-14 
9-70 
17T5 
7*45 | 
11-10 
18-27 
7T7 
9-85 
- 
17'31 
7-46 
10-85 
18-00 
7-15 
Mean Difference, . 
7*46 
Mean Difference, . 
1' 
7T5 
The heat of combination of any quantity of copper and zinc 
in the proportions stated, expressed as a fraction of the heat 
developed by the solution of the same quantity of the mixed 
metals in like proportions in nitric acid, is 
7*46- 71-5 _ 1 
7-46 — 24* 
The absolute amount of heat evolved in the solution of one 
gramme of the mixed metals (70 per cent, copper, 30 per cent, 
zinc) and of one gramme of an alloy of the same metals, in the 
same proportions, determined as on the previous occasion, is 
