Lf. A. Hill—WNotes on Argon and Helium. 361 
Now the pertinency of the question about argon and mer- 
eury vapor is this. Every fact which seems to be against the 
theory of monatomicity increases the probability that some 
one or more of these various explanations of the apparent 
inconsistency between the specific heat ratio and the conclu- 
sions drawn from the Periodic Law, may be correct. These 
explanations have not all the certainty of geometrical demon- 
strations, and if the verdict on them is, for instance, “ very 
probable but not fully proven,” then every additional argument 
strengthens the probability. 
Of course, by far the strongest argument against mon- 
atomicity is the Periodic Law, but what we are looking for, I. 
take it, is additional evidence. 
I have already remarked (I. c., p. 412-413) that the nascent 
or monatomic state of the element is, par excellence, that in 
which chemical affinity has its maximum development, and 
that all our chemical experience leads us to associate chemical 
affinity with the free and uncombined atom. Why then, if 
argon be monatomic, that is free and uncombined, has it no 
chemical affinity at ordinary temperatures ? 
Because (it is replied), at those temperatures it is already 
heated above the point at which chemical combination is pos- 
sible, and as when we cool mercury vapor from 800° down 
towards the point at which it assumes the liquid state, it begins 
to exhibit chemical affinity, so were argon likewise cooled 
down towards the point at which it begins to liquefy (—189-6°), 
it also would probably exhibit chemical affinity. Now even were 
this true, the monatomicity of argon would not thereby be 
directly proven; we should merely have removed one great and 
almost insuperable objection against the monatomic theory. 
But on the other hand, if it be not true, then it would be very 
difficult, if not impossible, to still hold the monatomic theory. 
Unfortunately, thus far no experiments have been published 
showing whether or not argon, near the low temperature at 
which it becomes liquid, exhibits chemical affinity.* Were this 
shown to be so, the case for monatomicity would be thus far 
strengthened, in that a great objection to the theory would 
have been removed; but our present knowledge of the prop- 
erties of argon does not lead us to expect the display of any 
such affinities, for the only approach to an argon compound 
thus far made has been effected by apparently increasing 
*The suggestion that argon compounds will only be formed at low tempera- 
tures, which follows directly from the assumption as to argon being too hot to 
combine, was made in the Educational Times, April 1, 1895, p. 479, and by Mr. 
C. J. Reed, Chem. News, May 3, 1895, p, 213. 
