44B 



§ 2. After the calibration was completed the manometer was put 

 into connection with a vapour pressure tube. This tube was of the 

 form described in the previous communication. The measurements 

 were conducted in the following manner. The apparatus was fiist 

 exhausted as far as possible and was allowed to stand for some 

 days, until the walls did not give off any more air. The vapour 

 pressure tube which was placed in a cryostat together with a ther- 

 mometer and a stirrer was then successively surrounded by ethylene, 

 methane and oxvgen, and the vacuum was measured at temperatures 

 between — 130° C. and — 180° C. Carbon dioxide was then distilled 

 into the apparatus and the vapour pressure measured at a series of 

 temperatures. The difference between the two readings at each tem- 

 perature after correcting for the thermal molecular pressure gives 

 the vapour pressure of carbon dioxide. 



In order to be able to obtain the corrections for the thermal 

 molecular pressure it is necessary to work with different tubes 

 suitably chosen. In this investigation two tubes were used, tube I 

 with a diameter of 1.75 cm. and tube II of 0.563 cm. 



