LE. A. Hill—WNotes on Argon and Helium. 363 
finally dissociated into atoms. The foree of molecular aggrega- 
tion is a maximum when heat energy is a minimum. With 
increase of temperature the force of aggregation between like 
atoms (as I and I for example) is finally weakened, so that in 
the liquid or gaseous state the affinity of unlike atoms for each 
_ other becomes the stronger force. Atstill higher temperatures, 
even these forces are overcome by the repulsive action of heat. 
We way say that heat overpowers the forces of aggregation 
{like with like) first, and those of chemical affinity (like with un- 
like) later and with more difficulty. Now mercury at 800° has 
reached this latter stage, and it is claimed that argon at ordi- 
nary temperatures is in the same condition. 
The analogies of argon are evidently with such elements as 
H, N, O, F, and Cl, that is to say with the metalloids of low 
atomic weight and specific gravity, gaseous at ordinary tem- 
peratures, somewhat soluble in water, with very low melting 
and boiling points, and very difficult to reduce to the liquid 
and solid state; rather than with the metals, among which 
mercury must be grouped, characterized by bigh atomic weights 
and specific gravities, liquid or solid at ordinary temperatures, 
insoluble in water, with much higher melting and boiling 
points, and easily reduced to the liquid and solid state. 
In endeavoring to draw conclusions as to the argon molecule, 
it would therefore seem less forced to reason from what we 
know of the former, the metalloids, which it closely resembles, 
rather than the latter class of bodies, the metals, with which it 
has but few analogies. We are thus led to regard argon as a 
body in which the atoms in the molecule (if di- or n-atomic) 
are very firmly bound together, like nitrogen for example, and 
in fact from whatever side we approach the question we are 
struck with certain marked analogies existing between these 
two elements. The inert character of nitrogen and its disin- 
clination for direct combination with other substances, has 
always been regarded as proving the strength of the force 
aggregating its atoms into a molecule, rather than showing that 
the substance is monatomic, and at a temperature so high that 
it is above or near the point at which combination is no longer 
possible; and why not also in the case of its analogue, argon ? 
Of the five gaseous elements to which argon is most closely 
analogous, H, N, O, F, Cl, all are at all ordinary temperatures 
far below the point at which combinations with other elements 
are impossible, and why should it be thought that argon is in 
any way different from them and above instead of below that 
temperature ? 
Let us consider the following table: 
