530 
.MK. T. J. BAKER ON THE THERMO-CHEMISTRY 
940° C., the violent action, before mentioned, is not necessarily the consequence of 
chemical union, but may be due to volatilisation of the zinc. 
The difficulty of making a quantitative determination of heat evolution under such 
conditions appeared too great to be overcome. 
The only recorded instance of sucli an attempt is to be found in Lord Kelyix's 
lecture at the Loyal Institution in May, 1897, on “ Contact Electricity in Metals,” 
where it is stated that Sir W. C. Loberts-Austex observed an evolution of 36 
calories jjer gramme of brass formed by the mixture of 30 parts of zinc with 70 parts 
of molten copper. 
No details of the experiment are given. 
A more promising method consists in the determination of the differences between 
the heats of dissolution, in a suitable solvent, of various alloys of copper and zinc 
and of the free metals when merely mixed in the same projjortions. 
This method has been adopted in the present paper. 
Preparation of A Hoys. 
The copper employed in making the alloys was the best electrolytic, which had been 
melted, and then rolled into sheet. 
Analysis showed it to be free from arsenic and bismuth, but it contained about '15 
per cent, of lead and a trace of iron. 
The zinc used had been re-distilled. It was free from arsenic and cadmium, but 
contained '06 per cent, of iron and a trace of lead. 
It dissolved in hot dilute sulphuric acid only after very prolonged immersion. 
Alloys containing more than 30 ])er cent, of copper were made by adding the 
requisite weight of zinc to the copper, which had beeii previously melted in a carbon 
crucible under a layer of powdered charcoal, and thorough admixture was secured by 
vigorous stirring with a charred stick. 
In making alloys containing less than 30 per cent, of copper it was found advan¬ 
tageous to melt the zinc and add the solid copjDer to it. The latter soon dissolved if 
the crucible was kept at a suitable temperature. 
It was easier to make an alloy, lich in zinc, of a pre-determined composition in this 
manner than by adding zinc to molten copper'. 
The alloys were cast in an iron mould yielding jjlates about 7 centims. X 2"5 
centims. X ‘5 centim. and weighing some 70 grammes. 
Their outer surfaces were then removed by filing and the central portions of the 
ingots were used in the experiments. 
The composition of each alloy was carefully determined by estimating the copj^er 
electrolytically. 
In certain experiments, afterwards abandoned, Dutch metal leaf and bronze 
powders were used. 
