i 898—99.] Dr Galt on Heat of Combination in Alloys. 619 
Preliminary Note of Experiments showing Heat of 
Combination in the formation of Alloys of Zinc 
and Copper to be Negative when the Proportion 
of Copper is less than about 30 per cent. By 
Alexander Galt, D.Sc. 
(Read May 1, 1899.) 
In March of last year I communicated to the Society a paper 
giving a detailed account of the procedure adopted in an experi- 
mental investigation, which I had undertaken at the request of 
Lord Kelvin, on the heat of combination of pairs of solid metals 
in the formation of alloys, along with a statement of some results 
which had then been obtained. 
The pairs of metals chosen were copper-zinc and copper-silver, 
and, briefly restated, the experiments were conducted as follows : — 
About half a gramme of alloy, reduced to powder by means of a 
file, was dissolved in dilute nitric acid, and an equal weight of a 
mixture of the same two metals in the same proportions was 
also dissolved under exactly similar conditions. The difference 
between the initial and final temperature in each case is an in- 
dication of the heat of solution. If the two results are the same 
then there is no heat of combination in the formation of the par- 
ticular alloy tested. But if the heat of solution of the mixture 
exceeds that of the alloy, then there must be heat of combination 
in the formation of the alloy equal to that difference. The experi- 
mental results, then, afford a means of approximately determining 
in absolute measure the heat of combination of the metals in the 
formation of an alloy. 
The investigation has been continued since my last communica- 
tion, and I expect to have it finished and to communicate the 
results to the Society either towards the close of the present session 
or at the beginning of the next. Altogether twenty- one different 
copper-zinc alloys, varying in composition from 5 to 90 per cent, 
of copper, and also five copper-silver alloys, containing from 10 to 
65 per cent, of copper, are under observation. 
