( 874 ) 
Physics. — “Researches on the Jourm-Keuvin effects especially at 
low temperatures. IL. The Jouum-Kruvin effect for air at 0° C. 
and at pressures up to 42 atmospheres.” By J. P. DALTON, 
M.A., B.Se., Carnegie Research Fellow. Communication 109¢ 
from the Physical Laboratory, Leiden. 
§ 1. In the preceding communication the conclusion was reached 
that the conditions under which OuszewskKr's expansions took place 
were not those whose fulfilment is necessary for the realisation of 
a true Jouuw-KerLviN process. The present communication offers further 
justification for that conclusion; it shows that special precautions are 
necessary before a reduction-valve apparatus, such as OLSZEwskI used, 
will give a true JouLE-KrLvin effect, and deals with the experiments 
leading to, and with the construction of, a reduction-valve apparatus 
particularly adapted to a determination of Jourr-KerLviN effects at 
low temperatures. The results obtained with this apparatus in the 
case of air at 0°C. are in good agreement with those calculated 
from the isotherms, and also with those experimentally determined 
by Joure and Kervin. 
§ 2. The calculation from the isotherms was made in the same 
manner as that for hydrogen (see § 6 Comm. 1097). Three terms of 
the empirical equation of state seemed sufficient for the present 
purpose. It may, therefore, be written 
B ual 
ea let ete «ww ye eye oe 
and leads to the relation 
dB 4 
pen 
WY Id Al Ta Al ad: 
Cri Tj — Neel) ot 
ie dC dB | 
A 0 dE — 265 
1 dT ch F a: 
bn ef |@-2,) -- - 6) 
The values of the virial-coefficients for air were kindly placed at 
my disposal by Professor KAMERLINGH ONNES; at present they are 
known only for individual isotherms, and, therefore, the evaluation 
of their rate of change with temperature cannot be made with the 
same degree of accuracy as was the case with hydrogen; it is, 
