58 THE ROYAL SOCIETY OF CANADA 



mixtures with the composition of the vapour and liquid phases are 

 now given in this paper. 



Measurement of Temperature 



Temperatures were measured by means of a Cu-Const. thermo- 

 couple, the E.M.F. being read on a slide wire potentiometer. An 

 accumulator was used as a source of electric supply and a Weston cell 

 as a standard. 



The fixed points chosen for calibration were^: 

 Boiling point of Nitrogen 77-3 abs. 

 « « « Oxygen 90-0 " 



« « " Methane 109-0 " 



at atmospheric pressure. The reference junction of the thermocouple 

 was kept in melting ice. 



Variations in the E.M.F. of the accumulator were corrected by 

 frequent comparison with the Weston standard. 



Gases Used 



The Methane, oxygen and nitrogen used were all obtained com- 

 mercially. 



Methane 



This was obtained from Messrs. Insoles, Cymmer Collieries, 

 Forth, Wales, and had a purity of 95% to 97%. The impurities, 

 carbon dioxide, oxygen, nitrogen and hydrogen were removed by 

 absorption and liquefaction followed by fractional distillation. 



Nitrogen 



This was supplied by the British Oxygen Company from their 

 Birmingham Works, and was fairly pure. Any carbon dioxide present 

 was absorbed in potassium hydroxide solution and the remainder 

 liquefied. It was found to boil away at a fairly constant temperature. 



These gases were stored separately in aspirator bottles over boiled 

 water containing caustic soda in solution. These bottles were gradua- 

 ted roughly in half-litres. When a mixture was to be made, the two 

 gases were admitted to the cryostat in the proportions desired, approxi- 

 mately, and liquefied. 



This mixture, after a reading of it was taken, was stored in a 

 third bottle and reserved for making other mixtures. 



No attempt was made to prepare mixtures of a known composition 

 but merely to obtain mixtures in sufficient variety for the purpose. 



1 Kaye and Laby's, Phys. and Chem. Constants. 



