36 THE ROYAL SOCIETY OF CANADA 



into a small thick-walled glass observation tube, surrounded by a cool- 

 ing bath in a cryostat. In these experiments, the cryostat contained 

 liquid ethylene boiling under reduced constant pressure, which pro- 

 duced and maintained the required temperatures. The observation 

 tube was connected by glass and steel capillary tubes to the air reser- 

 voir, and Cailletet pressure apparatus. By holding the cryostat at 

 any desired temperature, the air could be forced into the observation 

 chamber by slowly increasing the pressure in the Cailletet apparatus, 

 and the condensation phenomena could be observed. 



The observation tube, attached capillary, and enclosed stirrer 

 are the same as used by Crommelin, in his work on argon and are des- 

 cribed in Comm. No. 115, §2. This part of the apparatus was used with- 

 out modification, except that during the course of the experiments, the 

 observation chamber was opened and the entire tube with capillary 

 stirrer and glass thread for operating the stirrer were cleaned, and the 

 tube closed again. Of course, this operation changed the volume 

 slightly. The steel capillary tubes are the same as have been used in 

 so much of the work in the Leiden Laboratory. The Cailletet pressure 

 apparatus and glass reservoir tube are described in Comm. No. 69 

 also No. 97 a. Pressures were determined with the closed hydrogen 

 manometer described in Comm. No. 78. 



A Bourdon gauge was connected in parallel with the closed 

 manometer as a control and was very useful when applying pressures. 

 Temperatures were determined with two platinum resistance ther- 

 mometers, described in Comm. 141 a. The cryostat and the method 

 of using it are described in Comm. 83. As already mentioned the 

 glass capillary of the observation chamber was connected to the 

 Cailletet apparatus by steel capillary tubing. A short length of this 

 tubing joined the large reservoir to a two-way steel cock. From one 

 outlet of the cock, a steel capillary was connected to the observation 

 tube, as described, and from the other outlet, another steel capillary 

 was connected to a second reservoir or pipette filled with air. This 

 second reservoir was connected, so that if desired, a known amount of 

 air could be added to the stock in the main reservoir or removed from it. 

 The proportions of the main reservoir and the observation tube were so 

 well adjusted that the pipette was unnecessary, except for temperatures 

 well below the plait-point. 



The entire system of reservoirs, observation tube and connecting 

 tubes were carefully cleaned, dried and filled with air from which the 

 water vapor and carbon dioxide had been removed. The filling was 

 accomplished by first exhausting the tubes and then admitting air 

 very slowly through a drying trairi and a battery of tubes immersed 

 in liquid air. It was found that it was absolutely necessary to admit 



