[529] 
XII. The TJteniio-dieinisfini of the AIJoij.^ of ( ojyper and Zinc. 
By T. J. Baker, B.Sc. 
Communicated hy Professor J. H. Poynting, F.R.S. 
Keceived December 4, 1900—Read January 17, 1901. 
Introduction. 
It has l(Rig been known that the alloying of certain metals with each other is 
accompanied by evolution or absorption of heat, but in very few instances have any 
measurements of the thermal changes been recorded. 
There is now no reason to doubt the existence of definite atomic combinations 
between metals, and it lias therefore become a matter of considerable interest and 
importance to ascertain the heat of formation of these inter-metallic compounds. 
Laurie,"^ Charpy,! and others have adduced evidence pointing to the occurrence of 
chemical combination between copper and zinc in the making of brass, and an 
investigation of the thermo-chemistry of their alloys appeared particularly desirable, 
because a peculiar interest attaches to them in connection with Lord Kelvin’s 
calculation of molecular dimensions. 
During the progress of this work papers, dealing wholly or in part with the same 
subject, were published by Dr. Galt| and by M. Herschkowitsch §; further 
reference to these will be made in another place. 
Ch oice 0 f Mcth od. 
In making brass by the usual method, solid zinc is pushed beneath the surface of 
molten copper. 
A violent action is frequently observed, and this is often cited as indicating the 
occurrence of chemical action between the metals. 
Now copper melts at about 1080° C., but its temperature is doubtless higher when 
the zinc is added in the ordinary process of brass making, and since zinc boils at 
* ‘ Trans. Chem. Soc.,’ 1888, p. 104. 
t ‘Bull. Soc. d’Encouragement,’ Feb. 1896, pp. 33-34. 
I ‘Rep. Brit. Assoc.,’ 1898 and 1899. 
§ ‘ Zeits. f. Physik. Chemie,’ Nov. 1898. 
YOL, CXCVI.—A 285. 3 Y 
13.6.1901 
