Ly. A. Hill— Notes on Argon and Helium. 369 
positions, already called in question, and with due consideration 
of the requirements of the periodic law, makes out a pretty 
strong case, to say the least ; and yet even here the future may 
give us new facts and require us to modify our conclusions ; 
and there is hardly one of the many who have written upon 
this question that feels like laying down the law dogmatically 
at the present time, certainly not myself. 
_ Since the publication of my previous paper, a notable dis- 
covery, that of helium, has been made by Prof. Ramsay, and 
the new gas has turned out to be a body very closely analogous 
to argon. As noted by the discoverer, both bodies resist spark- 
ing with O in presence of caustic alkali, both are unaltered by 
red hot magnesium. In each case the velocity of sound in the 
gas indicates approximately the value 1°66 as the ratio of the 
two specific heats, and although opinion is divided, says Prof. 
Ramsay and his colleagues, on the precise significance of this 
ratio, it appears to be most probable that in all cases, as in that 
of mercury, it points to the monatomicity of the molecule. 
In general, they say,* an increase in molecular weight is 
accompanied by a rise in the boiling point, whether in the case 
of compounds or of elements; and they argue that if argon 
possessed the atomic weight 20 and molecular weight 40 it is 
probable its boiling point would lie above that of chlorine 
instead of being —187° and below that of oxygen, as is actually 
the case. And this they consider points towards a molecular 
formula A’ rather than A’ and so corroborates the monatomic 
theory. 
It would seem to me, however, as if this conclusion did not 
follow so plainly as assumed. I have thrown the data upon 
which the argument is based into tabular form : 
Molecule 18 Neh 0? Ax 08 cl? Br? 1? 
Molecular weight, 2 28 32 40 48 cool 158 254 
Boiling point, Peg 194-42 = 189-7 187-0’ — 106° —33°6" +59" +184° 
Melting point, ? —214° ? —1896 ? —102° —72° +114 
Now whatever its atomic weight, the molecular weight of 
argon gas is 40, and if we argue anything at all from molecu- 
lar weights we shall, I think, be led to place argon in the above 
table (A? = 40) between O? = 32 and O° = 48, into which place 
its melting and boiling points (respectively —189-6° and —187°) 
cause it to fit fairly well. True its boiling point is a little 
lower, about 4°, than oxygen, while apparently it should be higher. 
Perhaps later determinations of these points may clear up the 
anomaly, which is hardly greater than the limits of possible 
error (in certain directions), or perhaps oxygen, as indicated by 
the researches of Baly,+ may turn out to be a compound and 
* Journal Chem, Society, July, 1895. 
+ Chemical News, April 5, 1895, p. 169. 
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