262 Scientific Intelligence. 
helium on this assumption is 2°13 X 2= 4:26. But again we 
assume, in making this calculation, that helium is a single ele- 
ment, and not a mixture of elements. Before discussing this 
question, it appears advisable to inquire whether there is any evi- 
dence which would corroborate the deduction that it is a mon- 
atomic element. This evidence must be sought for in the proper- 
ties of argon, for those of helium have not as yet been sufficiently 
investigated. 
_ We know from countless examples among compounds of hydro- 
gen and carbon that increase in molecular weight is accompanied 
by rise of boiling point; and it may be stated as a proved fact 
that a polymeride has always a higher boiling point than the 
simpler molecule of which the polymeride is formed. Among 
the substances germain to this inquiry, ozone and oxygen may be 
cited; the complex molecule of ozone is shown by the higher 
temperature at which it boils. It might be concluded with cer- 
tainty, therefore, that A,, could it exist, should have a higher 
boiling point than A. 
Next, it is generally the case that the boiling point of an ele- 
ment, provided it has not a complex molecule like that of sulphur 
and phosphorus, is lower, the lower its molecular weight. There 
are the well-known instances of chlorine, bromine, and iodine; 
but if it be objected that these all belong to the same group, we 
may cite the cases of hydrogen, —243°5°; nitrogen, —194°4°; 
and oxygen, —182°7°; and we may add chlorine, —102°. If 
argon possessed the atomic weight 20 and the molecular weight 
40, it is probable that its boiling point would lie above that of 
chlorine, instead of, as is actually the fact, at —187°—below that 
of oxygen. But, it may be objected, the boiling point is deter- 
mined, not by the molecular weight, but by the density. It may 
be urged that the density of argon is 20, and that its molecules, 
like those of oxygen and nitrogen, are diatomic, in spite of the 
argument to the contrary from the ratio of specific heats. The 
answer to this objection is obvious; if this were so, its boiling 
point should lie above, and not below that of oxygen. 
These considerations cannot, of course, be accepted as evidence, 
but merely as corroborative of the conclusion as regards the 
monatomicity of argon. If they apply to argon, they apply 
with equal force to helium; and if they are accepted, it follows 
that the atomic weight of helium is 4°26. 
It is again necessary to consider the character of argon in 
attempting to answer the next question: Are argon and helium 
single elements or mixtures of elements? But before discussing 
it, let us consider another question: How does argon happen to 
occur in the air and helium only in minerals? Why is helium 
not present in air? A satisfactory answer to the question is, we 
think, contained in a paper by Dr. Johnstone Stoney (Chem. 
News, 1895, Ixxi, 67). He there shows that were hydrogen to 
be present in air (and it might be present, in spite of the oxygen 
with which it could be mixed, for a small quantity would surely 
