670 
1. All the apparatus and connections were reduced to a high 
vacuum and then washed out with argon. 
2. The cryostat was filled with the liquid gas desired (O,, CH,, 
ar ©. iH). 
3. The argon was admitted to the compression tube A, and then 
pumped into the dilatometer. 
4. The argon meniscus was adjusted to the upper part of the 
stem of the dilatometer, and the tap &, was closed. 
5. When the temperature is constant the position of the argon 
meniscus is read, the temperature is measured, and also when requi- 
red, the pressure registered by the hydrogen manometer. 
6. By reducing the pressure in the cryostat transition is made to 
a lower temperature, the same measurements are repeated; a lower 
temperature is then installed and so on until the meniscus has sunk 
below the subdivided portion of the stem. 
7. Sufficient argon is then allowed to escape into the volumeno- 
meter to bring the meniscus to the lower part of the appendix 
below the dilatometer; the temperature, pressnre and volume of the 
escaped gas are measured. 
8. The measurements of 5° and 6° are repeated in the reversed 
order of temperature until the meniscus reaches the upper part of 
the appendix. | 
9. The argon still remaining in the dilatometer is transferred to 
the volumenometer, and the measurements of 7° are repeated. 
It is clear that these measurements yielded the data requisite for 
the calculation of the liquid and vapour densities at all the experi- 
mental temperatures. To these calculations we shall return in the 
succeeding section. 
The dimensions of the dilatometer were so calculated that one 
could finish off the temperature range for any particular substance 
by successive measurements; in this way only two measurements 
with the volumenometer were required to give both the liquid and 
vapour densities. 
§ 4. Calculations. In many respects the calculations were made 
in the same way as those of Comm. No. 117. It was of great 
advantage to us that so many data are already available for argon, 
and that we could already make use of the reduced equation of 
state, VII. A. 8 *). We shall, however, here give a short summary 
of the method adopted in the calculations. 
Working from the very accurate calibration of the dilatometer, 
1) Proc. June 1912, Comm. no. 128, 
