1897-98.] Dr A. Galt on Heat of Combination of Metals. 147 
Thus the heat of combination of '7673 gramme of silver with 
*2327 gramme of copper is 18 (gramme-water) heat units Centi- 
grade. 
But it has been shown on page 143 that the heat of combina- 
tion of one gramme (*52 gramme copper and ’48 gramme of zinc) 
of the mixed copper and zinc filings was 76*6 (gramme- water) heat 
units Centigrade ; therefore the amount of heat developed in the 
formation of the zinc- copper alloy is fully four times the amount 
evolved in the formation of the silver-copper alloy, the metals 
being present in each case nearly in the proportion of their 
chemical equivalents as usually observed in chemical reactions. 
The much higher result for the zinc-copper experiments is just 
what might be expected from the fact that in contact electricity 
the force of attraction between zinc and copper is greater than that 
between silver and copper. 
The other alloy of silver and copper was next tested, *8 gramme 
of the mixed metals or of the alloy being used. The alloy was 
made from exactly equal weights of the metals, but on analysis it 
was found to be 51*62 per cent, silver and 48*38 per cent, copper. 
Heat of Solution of *8 gramme (*413 gramme of Silver mixed with 
*387 gramme of Copper) of the Mixed Metals and of *8 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.° 
0.° 
C.° 
C.° 
C.° 
1210 
19 15 
7*05 
12-30 
19-20 
6-90 
12-00 
18-97 
6-97 
12-05 
18-95 
6-90 
11*60 
18-70 
71 
1220 
19-10 
6-90 
j Mean Difference, . 
7*04 
Mean Difference, . 
6-90 
The heat of combination of any quantity of copper and silver in 
the proportions just stated, expressed as a fraction of the heat 
