48d Dr. Travers, Mr. Senter, and Dr. Jaquerod. [June 19, 



We have thus three determinations of the pressure coefficient of 

 hydrogen at an initial pressure of 700 mm., to the third of which, 

 since it is the result of one measurement of P and one of P 10 o, and 

 was only carried out to make certain that our instrument was in good 

 working order before determining the pressure coefficient for helium, 

 we attach less weight than to the remaining values. The results of 

 the two experiments with helium are of equal value, each being the 

 result of two determinations of P and three determinations of P 10 o. 

 The mean values of the pressure coefficient for both hydrogen and 

 helium appear to approach 0-00366255, a number which agrees very 

 closely with the value obtained by Chappuis (0-00366254), and is 

 somewhat lower than that given by Onnes (0-0036627) as his final 

 result, though differing little from one of his three actual measure- 

 ments (0-0036625). 



The values of the coefficients at lower initial pressures, do not show 

 the same concordance as those at higher pressure, but they tend to 

 show that at very low pressures the pressure coefficient does not 

 assume a lower limiting value, the reciprocal of which should be the 

 melting point of ice on the absolute scale of temperature. That helium 

 and hydrogen have the same pressure coefficient, and that the coefficient 

 is independent of the pressure, suggest that whatever correction may 

 be necessary to reduce temperatures between 0° and 100° C. on the 

 scale of the hydrogen or helium constant-volume thermometer to tem- 

 peratures on the absolute scale, it must be very small. Further study 

 of the thermodynamic properties of these gases is necessary for the 

 solution of this important problem. 



Part II. — By M. W. Travers, G. Senter, and A. Jaquerod. 



Vapour Pressures of Liquid Oxygen. 



As has been shown in Part I, the coefficients of increase of pressure 

 at constant volume for hydrogen and helium, between 0° and 100° C, 

 have the same value, viz., 0-00366255 or 1/273*03. 



Numerous measurements of the boiling points and vapour pressures 

 of liquid oxygen on the constant volume hydrogen scale have been 

 made by previous investigators. The values obtained differ by two or 

 three degrees, and even the most reliable measurements vary between 

 - 182°*4 and - 182°-7 C. In very few cases are any experimental 

 details given in the original papers ; in most cases it is even impossible 

 to ascertain what value was taken for the coefficient of expansion 

 of hydrogen. In every case, however, it appears that the measure- 

 ments were made by immersing the thermometer in a mass of liquid 

 oxygen, and measuring the pressure under which the liquid was evapo- 

 rating. As is shown in our paper, it is extremely difficult to maintain 

 liquid oxygen in a steady state of ebullition, and unless a rapid current 



