J. W. Langley—Chemical Affinity. 437 
Art. LITI. coe A fintty * by Joun W. LANGLEY, 
or, Michigan. 
[Concluded from page 373.] 
Ill. Tae Existinc Prosiem. 
The history of the various modifications and additions 
which have been made to the primitive conception of the 
nature of affinity, when briefly summarized, appears to be this. 
Hippocrates held that union is caused by a kinship, either 
a 
believed affinity to be a force which unites unlike substances. 
Bergman and Geofrey taught that union is caused by a selec- 
tive attraction, and therefore they called it “elective “affinity.” 
Wenzel and his successors showed that affinity is definite in 
action and amount. It has limits, or proceeds per saltum. 
Berthollet contended that affinity is not definite; he proves 
that it is often controlled by the nature and the masses of the 
reacting bodies. Dalton, Berzelius, Wollaston and others, held 
on the contrary this force to be definite and to act per saltum. 
It is a power which emanates from the atom. Davy, Ampére 
and Berzelius believed affinity to a a consequence of electrical 
action. Avogadro, in one way, and Brodie in another, oS 
us affinity exerted b ihotectiiea as wel 
force which binds together not only particles of the same aah: 
stance but also of heter rogeneous substances. 
rom the fact of the actual existence of radicals and from 
the phenomena of substitution was developed the notion of 
agave and that therefore affinity Bath with the structure 
of t e body as well as with its composition. The difference 
Pca power has led to the doctrine of valence, which, if 
influence on theories of affinity, shows that this 
property pe matter has two distinct concepts ; one its power of 
attracting a number of atoms, the other its power of doing work 
or evolving energy. These two attributes seem to be in no 
. way related to each other. 
: Address before Section “C” of the American Association for the Advance- 
a, of erthog Philadelphia, 1884, 
