Magnetic Permeability of Liquid Oxygen and Liquid Air. 293 



oxygen at different temperatures, and shown that between the limits 

 of C. and 452 C. tbe magnetic susceptibility of oxygen (K) per 

 unit of mass is a function of the absolute temperature T, such that 



10 6 K = 33700/T, 



and that the value of K (per gram) at C. is, therefore, 123/10 6 . 

 The mass of 1 c.c. of oxygen gas at C. and 760 mm. is O0014107 

 gram, and, reciprocally, the volume of one gram is 708'9c.c. at C. 

 and 760 mm. 



Hence the magnetic susceptibility of gaseous oxygen at C. and 

 760 mm. per unit of volume (one c.c.) would be 123 x 0'00141 x 10~ 6 

 = 0'173 X 10~ 6 , which is not very different from that obtained by 

 other observers.* 



If then it could be supposed that gaseous oxygen followed the 

 same law down to 182 C., and taking the gas in a condition when 

 the density is nearly 0'00423, the volume susceptibility (&) at 

 182 C. would be 1*6 x 10~ 6 , and hence the permeability (/*)> where 



should be 1-00002. 



It is, however, certain that the susceptibility per unit of mass will 

 not continue to increase in accordance with the hyperbolic law, 

 because this would imply that at the absolute zero of temperature 

 the susceptibility would be infinitely great, and hence the above 

 number 1 '00002 gives a superior limit for the permeability of the 

 gaseous oxygen at 182 C. lying on the surface of the liquid oxygen.t 



The conclusion is that the correction to be applied to the above 

 observed value of ^ for the liquid oxygen, viz., T00287, to refer it to 

 a vacuum taken as unity, is altogether masked by the unavoidable 

 errors of experiment, and hence, pen ding further more exact measure- 

 ments, this may be taken as the value of the constant. We have, 

 however, at the present time, arranged a method which will enable 

 us we hope to determine directly the magnetic susceptibility of liquid 



* .Faraday, ' Experimental Researches,' vol. 3, p. 502, gives a value for the sus- 

 ceptibility of gaseous oxygen at 60 F., referred to an equal volume of water as 

 unity, which, when reduced to absolute values by taking the magnetic susceptibility 

 -of water as 0'79 x 10~ 6 , gives the value of the susceptibility as 0'143 x 10~ 6 . Becquerel 

 found a value not very different. 



f The critical temperature of oxygen is 118 C. The corresponding absolute 

 temperature is 155. If we then put T = 155, in Curie's formula, 10 6 K = 

 33700/T, we get 10 6 K = 217'4, as his deduced extrapolated value for the sus- 

 ceptibility per unit of mass. Since the density of liquid oxygen, as determined 

 by one of us (J. Dewar) is l'137o, our value for the susceptibility per unit of 

 mass of the liquid oxygen is 228/l'1375 = 2007. These figures show that the 

 hyperbola does not represent the value of the susceptibility per unit of mass below 

 -the critical temperature. 



