ELISHA MITCHELL SCIENTIFIC SOCIETY 17 
possible that the ideas to be advanced in the further discus- 
sion of this subject in this paper will meet with opposition. 
Certainly they should be fully and freely discussed if they are 
worthy of it. I believe that they form astep toward the 
clearing up of the mystery of valence. 
It is necessary, however, first to trace somewhat further 
the development of the original conception. One of its ear- 
liest and most important applications was to the study of the 
constitution of the compounds of carbon. Here Kekulé as- 
sumed for carbon a constant valence of four, and this idea is 
still dominant in theories relating to the constitution of these 
bodies, It was quite natural then that the first belief should 
have been in a constant valence. It was speedily found, 
however, that in certain cases, as in the compounds of nitro- 
gen and phosphorus, this belief was scarcely tenable. There 
were efforts at making it hold good, as, for instance, a dis- 
tinction was drawn between atomic and molecular com- 
pounds, but all of these suggestions have been proved unsat- 
isfactory. - 
We unquestionably have to account for the existence of a 
compound with three atoms and another with five atoms in 
the cases of nitrogen and phosphorus and there are many sim- 
ilar anomalies. Here the valence seems to vary toward one 
and the same element. Cases might be multiplied to show 
also that it varies often towards different elements. Thus it 
frequently happens that the valence of an element towards 
hydrogen seems to be quite different from that exhibited to- 
ward oxygen. For a long time there was much straining to 
consider the valence of an element always the same but this 
effort is, in large measure, abandoned now as unavailing and 
chemists admit that valence is not constant but variable and 
may even vary towards one and the same element. 
The doctrine of valence has had much added to it about 
bonds, affinities, and linkage, the necessity for which one may 
well question. Certainly the misuse of the word affinity, see- 
ing its other and greater use, should be earnestly discounten- 
anced. I am inclined to think that the other terms bring in 
false and misleading ideas which should be carefully guarded 
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