Page:Proceedings of the Royal Society of London Vol 60.djvu/319

Rh oxygen at different temperatures, and shown that between the limits of 0° C. and 452° C. the magnetic susceptibility of oxygen (K) per unit of mass is a function of the absolute temperature T, such that

10® K = 33700/T, and that the value of K (per gram) at 0° C. is, therefore, 123/10®. The mass of 1 c.c. of oxygen gas at 0° C. and 760 mm. is 0 0014107 gram, and, reciprocally, the volume of one gram is 7C>8'9c.c. at 0° C. and 760 mm.

Hence the magnetic susceptibility of gaseous oxygen at 0° C. and 760 mm. per unit of volume (one c.c.) would be 123 X 0 00141 x 10-6 = OT73xlO-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 (Jc) at — 182° C. would be 1*6 x 10-6, and hence the permeability (/*), where fi = 1 -f 47 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 l '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 fi 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, pending further more exact measurements, 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

unify, which, when reduced to absolute values by taking the magnetic susceptibility of water as 0 79 x 10 r>, gives the value of the susceptibility as 0'143 x 10—G. Becquerel found a value not very different.
 * Faraday, * Experimental Researches/ vol. 3, p. 502, gives a value for the susceptibility of gaseous oxygen at 60° E., referred to an equal volume of water as

t The critical temperature of oxygen is —118° C. The corresponding absolute temperature is 155°. If we then put T = 155, in Curie’s formula, 106E! = 33700/T, we get 106K = 217'4, as his deduced extrapolated value for the susceptibility per unit of mass. Since the density of liquid oxygen, as determined by one of us (J. Dewar) is IT 375, our value for the susceptibility per unit of mass of the liquid oxygen is 228/1T375 = 200 7. These figures show that the hyperbola does not represent the value of the susceptibility per unit of mass below the critical temperature.