362 Lf. A. Hill—WNotes on Argon and Helium. 
instead of decreasing the energy of the gas (combination with 
benzene).* 
There are, however, some experiments which seem to point 
against the monatomic theory. Thus Lord Rayleigh remarks 
as follows:+ “It has turned out that the gas possesses the same 
ie . 
value of _ as hydrogen, and that the value of this expression 
is not altered between —90° and +250° . . . . Argon there- 
fore shows no signs of association on cooling nor of dissocia- 
tion on heating.” The inference is that like change of temper- 
ature would have no greater effect on its chemical affinity 
than on its state of molecular aggregation. 
In the absence, however, of direct experiment to determine 
the point, we may pursue an indirect method. If we can, from 
the known properties of argon, determine the class of bodies 
to which it belongs and with which its greatest analogies are 
found, then whatever we can predicate of these bodies as a 
class, we can within reasonable limits predicate of argon also. 
If they, as a class, are at ordinary temperatures far below 
instead of above the point at which chemical affinity is over- 
powered by heat, then probably argon is likewise below rather 
than above that point; and if below, then the theory of its 
monatomicity has before it the very difficult task, of explain- 
ing away the lack of chemical affinity in the free atom of 
argon. 
Of course if the molecule is di- or »-atomie, its chemical 
inertness, like that of N’, is readily explained by the strength 
of the force aggregating the atoms in the molecule, which 
force opposes chemical affinity, since the force of affinity must 
first disintegrate the molecule before combination with other 
atoms can take place, that is, must first overcome the force of 
molecular aggregation. 
In general we may say of molecules, that starting with the 
minimum of heat in a solid and inactive state, as they acquire 
heat energy they become successively liquid, gaseous, and are 
* And I may add Berthelot’s combination with carbon disulphide, and more 
recently, Prof. Ramsay’s combination with incandescent carbon, Chem. News, 
Aug. 2, 1895, p. 51; in all which cases a large quautity of electrical energy is 
needed to bring about the combination. 
+ Nature, June 6, 1895, p 127. 
{It may occur to some that should argon prove a mixture of gases, the argu- 
ment fails, and as the evidence favors the mixture theory, the argument has but 
little weight. The conclusion, however, is incorrect. If argon is a mixture, its 
components are gases which resemble each other in chemical and physical prop- 
erties so closely, that up to the present time no method of separating them has 
been discovered. Hence any iuference as to the properties of this mixture, 
which we call argon, must apply with equal correctness to all constituents present 
in quantity. But if argon is a mixture, the apparent conflict with the periodic 
law may be explained by the presence of two gases, of different densities, but 
similar chemical and physical properties. 
