( 608 ) 
in the stem of the piezometer (immersed in a water bath at about 
20° C.) were read off in the two measurements that formed each 
vapour pressure determination. As the cross-sections of the reservoir 
and of the piezometer stem were known and the temperature of the 
waterbath was noted, and as, moreover, the density of the gaseous 
argon in the stem could be calculated from argon isotherms which 
will soon be published by Prof. KaAMERLINGH ONNES and myself‘), 
all the data necessary for the calculation of the difference between 
the liquid and vapour densities were known. For the mass of the 
gas by which the quantity in the stem has been lessened during 
condensatiun is equal to the mass of liquid formed m/s the mass 
of saturated vapour that at the beginning of condensation occupied 
the space taken up at the end of condensation by the liquid that 
has been formed. In the calculation a correction has been made for 
the volume of the glass stirrer in the low temperature reservoir 
§ 2. The results lay no claim to an accuracy equal to that of 
the vapour pressure determinations in the paper referred to. The 
accuracy can be estimated at from 1 to 1'/, °/,, but the fact that 
nothing is knewn concerning the liquid and vapour densities of 
argon in the region covered by my experiments seemed to me to 
justify the publication of these results. The calculations (in which, 
of course, allowance was made for the small impurity in the argon) 
could be made only for series VI, V, ILI, and IV, and II of Comin. 
115, since the temperature in the two series VII and IX was in 
the immediate neighbourhood of the critical temperature, and the 
meniscus was too unsteady to allow of fairly sharp readings. 
The results obtained are collected in the following table. As 
usual the subseripts 1 and 2 refer to the liquid and vapour states 
respectively; the densities are given with respect to water at 4° C. 
Date Series | t p’) | d,—d, 
| | ; 
1910. 10 Febr. vi | —140.80 22.185 0.9195 
10 > V —134.72 29.264 7118 | 
9 » \ Hand IV | —129.83 35.846 | 6502 | 
9 » | I] —125.49 | 42.457 eer ce 
1) In the present paper frequent use is made of these isotherms. 
2) For the sake of completeness vapour pressures (already published in Comm. 
115) are here inserted in the table. 
