( 617 ) 
§ 3. For description of the apparatus used for determinations of 
the normal volume and of the individual isotherms we may refer to 
earlier publications '). In one respect we introduced an improvement 
for we took our readings through a telescope with a micrometer eve 
piece; in this way they could be made at twice the rate possible when 
using the nonius of the cathetometer. Pressure and temperature 
readings were made in exactly the same manner as before in deter- 
minations of vapour pressures etc, *) and the remarks made in the 
communication of those results apply equally well here. Measurements 
of pressures below 20 atm. were made with the standard open 
manometer. *) 
We gratefully acknowledge our indebtedness to Miss G. LL. LORENTZ 
and Mr. W. J. pr Haas for their measurements and calculation of 
the temperatures, and also to Dr. C. Dorsman Jr., and Mr. G. Horst 
for their measurements with the open manometer. 
§ 4. As regards the calculations themselves we may also refer to 
earlier communications *) for there is not much fresh to be said about 
them. First, isotherms for + 20°C. and 0° C. were calculated using 
the expansion coefficients for oxygen taken from an earlier paper *) ; 
the critical constants for argon and oxygen differ but slightly from 
each other. Then the coefficients of the empirical equation of state *) 
Ay and B4 were calculated to a first approximation, and using the 
critical constants‘) a value for Cy was got from the set of reduced 
coefficients VII. 1 *). From the equation to which tbe operations led 
the expansion coefficients for various densities were calculated, and 
with these values the calculation of the isotherms was repeated. From 
these new isotherms to a second approximation, the coefficients were 
recalculated to a second approximation. For our present purpose a third 
approximation was found to be unnecessary. 
The expansion coefficients at low temperatures which were neces- 
sary for the much smaller corrections for that portion of the glass 
capillary inside the cryostat were at first deduced from AMAGAr’s *) 
1) Proc. April 1901, Comm. NP 69, Proc. April 1902. Comm. NO, 78, Proc. 
Sept. 1906, Comm. N°. 94f, Proc. March 1907, Comm. N°. 97a, 
2) Proc. May 1910, Comm. NO, 115. 
3) Proc. Nov. 1898. Comm. N° 44. 
4) Proc. April 1902, Comm. N®. 78, Proc. March 1907, Gomm. N’. 97a. 
5) Proc. April 1902, Comm. N°. 78. 
6) Proc. June 1901, Comm. N°. 71. 
7) Proc. May 1910, Comm. N’. 115. 
8) Suppl. N°. 19. (May 1908) p. 18. 
9) E. H. Amacar. Ann. d. Chim. et d. phys (6). 29, June and Aug. 1893. 
