On the Materiality of Caloric. 615 
bodies; andthe properties of the substances so 
changed are also materially altered. Now this 
is the only unequivocal mark of chemical union, 
that we can apply in any instance ; and chemical 
union implies the existence and efficiency of 
chemical affinity. 
2. The relation of caloric to different sub- 
Stances appears to observe that peculiar law, 
which, in other instances, is termed elective 
affinity, If a compound of two or more prin- 
ciples, a metallic oxyd for instance, be exposed 
in a high temperature, the caloric forms a per- 
“manent union with the one, but not with the 
other. In certain instances, caloric is evolved, 
when two substances, attracting each other more 
powerfully than they attract caloric, produce on 
admixture, an elevation of temperature. In 
other instances, caloric is absorbed, when it is - 
attracted by the new compound, more strongly 
than by the separate components. Such facts 
warrant the deduction, that caloric is subject to 
the laws of chemical affinity.—But the precise 
order of its affinities remain to be decided, by 
future experiments. 
g. Caloric seems, also, on some occasions, 
to bear a part in the operation of double elective 
affinities. In this way, it produces decompo- 
sitions, which, by single affinity, it is ais aut? 
VOL, Vv. PP 
