1897-98.] Dr A. Galt on Heat of Combination of Metals. 137 
Heat of Combination of Metals in the Formation of 
Alloys. By Alexander Galt, D.Sc. 
(Read March 7, 1898.) 
In the course of his valuable researches on the heats of com- 
bination and decomposition of bodies, the late Professor Thomas 
Andrews, of Belfast, arrived at the conclusion that “If three 
metals, A, B, C, he so related that A is capable of displacing B and C 
from their combinations, and also B capable of displacing C ; then 
the heat developed in the substitution of A for C will he equal to 
that developed in the substitution of A for B, added to that de- 
veloped in the substitution of B for C ; and a similar rule may 
he applied to any number of metals similarly related.” A tabular 
statement of experimental results is given, and from them illustra- 
tions of the above conclusion may be obtained. Por example, let 
A represent zinc, B lead, and C copper ; then, for equivalent 
quantities of the metals, it was found that the number of (gramme - 
water) heat units centigrade developed when zinc displaces copper 
is approximately equal to the number developed when zinc dis- 
places lead, added to that obtained when lead displaces copper. 
But, in contact electricity, the electromotive force between zinc 
and copper is equal to that between zinc and lead added to that 
between lead and copper. These facts led Andrews to make the 
following important remark : — “ Electromotive forces which are 
really due to contact of dissimilar bodies are also the very forces 
which cause heat when chemical combination ensues, potential 
energy being converted into kinetic energy by the rushing together 
of the particles under attracting forces.” 
Lord Kelvin * has investigated the question of the amount of 
heat equivalent to the work done by polished parallel plates of 
copper and zinc kept metallically connected by a flexible wire, and 
allowed to attract one another to very small distances, such as the 
* Popular Lectures and Addresses , vol. i., “The Size of Atoms,” pp. 
160-166. 
YOL. XXII. 14/9/98 
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