DURING METALLIC SUBSTITUTIONS. 
103 
be heated by the precipitation of one gramme of the metal from a solution of any of 
its salts ; and that those in the second column express the degrees through which 
the same weight of water would be raised by the precipitation of an equivalent 
(oxygen —1) of the same metal. 
If three metals. A, B, C, be 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 be equal to that developed in the substitution of A 
for B, added to that developed in the substitution of B for C ; and a similar rule may 
be applied to any number of metals similarly related. Several illustrations of this 
principle are afforded by the preceding table. Thus 
1 equiv. lead displaced by zinc 2357° 
1 equiv. copper by lead 1061 
1 equiv. copper by zinc 3418 
The experimental result for the last case is 3435°, which in such inquiries may 
be considered to be identical with the theoretical number. Again, 
1 equiv. copper by zinc 3435° 
1 equiv. silver by copper ....... 2176 
1 equiv. silver by zinc 5611 
The experimental result is 5747°, which differs ^rd part from theory. This dif- 
ference only corresponds to an error of about 0°’04 among the three experiments, and 
the agreement may therefore be considered satisfactory. By applying the same prin- 
ciple, we can easily deduce the amount of heat developed in other cases of metallic 
substitution. Thus an equivalent of mercury displaced by zinc should give 731 units 
of heat, of platinum displaced by copper 7650 units, by mercury 6919 units, &c. 
