1903.] Measurement of the Pressure Coefficient of Oxygen. 379 



" On the Measurement of the Pressure Coefficient of Oxygen, at 

 Constant Volume, and different Initial Pressures." By 

 WALTER MAKOWER, B.Sc., and HENRY R NOBLE, B.Sc. Com- 

 municated by SIR WILLIAM RAMSAY, K.C.B., F.R.S. Received 

 June 26, 1903. 



The Pressure Coefficient of Oxygen. 



1. Introduction. Travcrs and Jaquerod have recently carried out a 

 series of measurements of the pressure coefficients of hydrogen and 

 helium, and, in conjunction with Senter, have applied their results to 

 the measurement of the vapour pressures of liquid oxygen and liquid 

 hydrogen on the constant volume helium and hydrogen scales.* At 

 the conclusion of this research Dr. Travers suggested that we should 

 make an attempt to determine the pressure coefficient of oxygen, 

 which seemed to present those peculiar difficulties which are always 

 associated with measurements involving the observation of mercury 

 surfaces in contact with this gas. The apparatus employed has been 

 previously described by Travers and Jaquerod. f 



2. Previous Determinations. Regnault attempted to measure the 

 pressure-coefficient of oxygen, but failed to obtain concordant results. 

 He attributed his failure to the oxidation of the mercury in the 

 manometer used to measure the pressure of the oxygen.! 



Von Jolly obtained the value 0-0036743 as the mean of eighteen 

 observations at an initial pressure of about 760 mm. The individual 

 observations are, however, very discordant, varying between 0-003680 

 and 0-003668. 



3. Preparation of tlie Oxygen and its Introduction into the Thermometer. 

 The oxygen used was prepared by heating pure dry potassium 

 permanganate. The oxygen so generated was passed over soda-lime 

 and liquefied by passing it into a glass spiral immersed in liquid air. 

 By lowering the vessel containing the liquid air, the oxygen could be 

 allowed to boil off gently. In this way any trace of water vapour or 

 other impurity which might have been present was completely removed. 



The method of introducing the gas into the thermometer was pre- 

 cisely the same as that employed by Travers and Jaquerod.|| 



The thermometer bulb, which at the beginning of the research con- 

 tained helium, was exhausted to a high vacuum, along with the 

 apparatus employed for generating the oxygen. The thermometer was 

 then filled with pure oxygen and after a short time again exhausted. 



* ' Phil. Trans.,' A, Tol. 2CO, p. 105. 

 f Loc. cit. 



I ' Fogg. Ann.,' vol. 55, p. 391, 1842. 



' Pogg. Ann./ Jubelband, p. 82, 1874. 



II Loc. cit. 



