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LXX. Notices respecting New Boohs. 
Bulletin of the Bureau of Standards. Yol. IV. No. 3, Jan. 1908. 
Washington: Government Printing Office, 1908. 
The contents of this issue include an important paper by W. A. 
Koyes and H. C. P. Weber on the Atomic Weight of Chlorine. 
The method employed consists in weighing the hydrogen absorbed 
in palladium and the chlorine in the form of potassium ehloro- 
platinate. The hydrogen is passed over the heated chloroplatinate, 
hydrochloric acid being formed which is condensed and weighed. 
The mean value found is 35-184 (H=l). 
The part contains also a critical paper by W. W. Coblentz on 
instruments and methods used in radiometry, in which the relative 
merits are discussed of a radiomicrometer, linear thermopile, 
radiometer and bolometer. The thermopile is recommended on 
account of its greater steadiness for measuring very weak sources 
of radiation, e. g. the extreme ultra-violet and infra-red region of 
the spectrum. The other articles are the preparation of chloro- 
platinic acid by electrolysis of platinum black, by H. C. P. Weber : 
the self-inductance of a coil of any length and any number of 
layers of wire, by E. B. Eosa ; the self-inductance of a solenoid 
of any number of layers, by Louis Cohen; a quartz compensating 
polariscope with adjustable sensibility, by P. Pates. 
LXXI. Intelligence and, Miscellaneous Articles. 
ON THE MIXING OF GASES. 
To the Editors of tlie Philosojrfiical Magazine. 
Gentlemen, — 
f BEGBET that my absence in Egypt during February and 
-*- March prevented my seeing Professor Orr's paper in your 
February number till quite recently. I have since contributed to 
' Science Progress ' an article in which my views on the questions 
which he raises are explained more at length. I do, however, 
doubt whether there is any proof that the mixture of two gases 
by diffusion is an irreversible process. It is of course true that if 
we have two mixtures of (say) oxvgen and nitrogen at the same 
pressure and temperature, in one of which oxygen, and in the 
other nitrogen, preponderates, then if we remove the partition 
which separates them, they at once begin to mix more uniformly. 
But as that would equally be the case if the process of diffusion 
were periodic, the observed fact is no proof that the process is not 
periodic. Theoretically 1 maintain that no irreversible motion is 
possible among the molecules of a gas, if the kinetic theory be true, 
and if the gas be completely isolated, that is completely protected 
from the influence of external bodies. Professor Orr, as I gather, 
will not accept the kinetic theory. In that he may be right. But if 
we do not accept it, is there any other theory that can be applied ? 
To prove experimentally that the diffusion process is irreversible 
would require that the experiment be continued for a time at least 
half as long as the period of the motion if it were periodic. How 
long a time would Professor Orr consider sufficient? Also to 
make the experiment at all conclusive, the diffusing gases must at 
every instant during the experiment be completely protected from 
all external influences. Has such an experiment ever been made? 
S. II. Buebuey. 
