THE NATURE OF VALENCE. 
By F. P. VENABLE. 1 
The term ‘‘ valence” is variously defined as the ‘‘combining 
capacity,” or ‘‘capacity of saturation,” ‘‘quantitative com- 
bining power,” or ‘‘chemical value of the atom.” It is well 
known that the introduction of this idea into chemistry was 
due to the development of. the type theory, a system which 
had at first purely empirical basis. Sixty years ago there 
was still some hesitation as to the acceptance of the atomic 
theory or the need for such a theory. Much use was made of 
the term equivalent, which had been Wollaston’s expedient 
for avoiding the difficulties arising from the full adoption of 
the theory of atoms. | 
Wollaston had been himself very far from consistent in the 
use of the term. The numbers called by him ‘equivalent 
weights’ were not infrequently atomic and molecular weights 
and fully as hypothetical as the so-called atomic weights of 
Dalton. Inthe later use of the term it signified solely the 
numbers obtained by analysis without the introduction of any 
theoretical considerations. Thus, on analyzing ammonia, 
the ratio 
N’: Hse 
is gotten, and therefore the equivalent of nitrogen is 4.6. 
Strange to say the equivalent given by Wollaston corresponds 
with the present atomic weight, whereas the atomic weight 
given by Dalton corresponds with what would be the equiva- 
lent. 
It is manifest that the idea of equivalents needed some- 
thing more than the simple theory of atoms to make it clear 
and tenable. It embodied two distinct conceptions and if we 
hold to an atomic theory we must introduce a further explan- 
atory theory of the saturation capicity of these atoms. This 
1 Address, as chairman, delivered before the North Carolina Section, 
