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fy. A. Hill—Notes on Argon and Helium. 359 
ArT. XXXVIII.—Some additional Notes on Argon and 
Helium; by Epwin A. HI. 
AN English scientist in a recent letter, referring to the point 
made in my article on argon,* as to the inconsistency of regard- 
ing a free or nascent monatomic atom as devoid of chemical 
affinity, asks the very pertinent question whether I have con- 
sidered the case of mercury vapor, which at 800° is monatomic 
and yet has practically no chemical affinity. I had indeed 
given this case some consideration, but lack of space kept me 
from referring to it in my previous article. 
Lord Rayleigh and Prof. Ramsay, in their original memoir, 
use the following language: “In conclusion, it need excite no 
astonishment that argon is so indifferent to reagents. For 
mercury, although monatomic, forms compounds which are by 
no means stable at a high temperature in the gaseous state, and 
attempts to produce compounds of argon may be likened to 
attempts to cause combination between mercury gas at 800° 
and other elements.” The assumption evidently being, that at 
all ordinary temperatures, argon is heated to a point above that 
at which chemical affinity is strongly manifested. 
Of course argon may yet prove to be either a mixture or a 
compound of elements, but assuming it to be a single element, 
the important question still remains unsettled as to the num- 
ber of atoms comprising its molecule. 
The ratio of the two specific heats, as derived from experi- 
ments on the velocity of sound in argon, has been shown to 
be about 1°65, approximating closely to 1°67, the value which, 
according to the theory of Clausius, proves the gas to have no 
energy of rotation. The conclusica, that therefore the gas is 
monatomic, depends on at least three things: 
Ist. On the correctness of the assumption that a gas, with 
little or no rotational energy, cannot be di- or n-atomic, but 
must be monatomic. In my article on argon (I. c.) I have endeav- 
ored to show, that the amount of rotational energy acquired 
by gaseous molecules will depend on the relation between the 
repulsive forces acting during the encounter, and the attrac- 
tive forces aggregating the atoms into a molecule; and that 
even if the rotational energy be but slight, di- or n-atomicity 
may be possible, and monatomicity does not therefore neces- 
sarily follow. 
2d. The conclusion also depends upon the correctness of the 
deduction of Clausius, that a ratio of the two specific heats of 
1:67 proves the gas to have no rotational energy. This is 
* This Journal, May, 1895, p. 413. 
