370 ff. A. Hill—WNotes on Argon and Helium. 
not a single element, as has been so long supposed ; or argon 
may be a mixture. At any rate, if boiling point is to be raised 
by an increase in molecular weight I see no reason for expect- 
ing A* = 40 to have a higher boiling point than Cl’ = 71; as 
the molecular weight is lower so also should be the boiling 
point, and to my mind the facts either prove nothing or else 
favor rather than oppose the diatomic theory. If the boiling 
point depends upon molecular rather than atomic weight, can 
the boiling point give us any help in determining the atomic 
weight and the number of atoms in the molecule? 
Some additional light seems to be thrown upon the subject 
by the recently determined refraction equivalent of argon. 
Mr. R. M. Deeley,* in his paper on this subject, after showing 
“that the refraction equivalents of the elements vary periodi- 
cally with much regularity,” remarks as follows: 
“Tf argon, like calcium, has an atomic weight of 40, we 
should expect its refraction equivalent to be also about 10. On 
the other hand, if its atomic weight be 20, and if it (argon) 
falls between fluorine and sodium, the refraction equivalent 
might be 3 or even smaller than that of fluorine (1°6), for 
between carbon {5 or 6) and aluminum (7:7) the refraction 
equivalents decrease rapidly until fluorine is reached. They 
then increase with increasing atomic weight, and more than 
regain their original value at aluminum. The refraction 
>) 
equivalent is calculated from P xX it (P = atomic weight, 
d = density, water taken as unity.) 
Now Lord Rayleight has recently shown that for argon p = 
1:000281. This value is certainly remarkable, and proves argon 
to be as anomalous in its action upon the waves of light as in 
its behavior as to specific heats. In spite of its greater density 
(about 1°38, air = 1°) its refraction is only ‘961 that of air; 
‘whereas, refraction usually increases with the density of the 
refracting medium instead of decreasing. | 
If A’=40 the refraction equivalent by the above formula 
becomes about 6:3 instead of 10, the value which Mr. Deeley 
says would be required, were it monatomic with an atomic 
weight of 40; but if A* = 40 whence A = 20 (the diatomic 
theory) the corresponding value of the refraction equivalent 
3°14 is entirely consistent with the position of argon in Men- 
deleeff’s classification in Group VIII between fluorine = 1°6 
and sodium = 4°3, 3°14 being very nearly a mean between these 
values; and as Mr. Deeley remarks (I. c¢.) “the equivalents 
decrease rapidly until fluorine is reached, and then increase 
with increasing atomic weight.” 
* See Chem. News, Feb. 8, 1895, p. 75. 
+ Nature, July 25, page 293. 
