596 Liquid Hydrogen Galorimetry. [March 25, 1904. 



In passing, it may be noticed that if the constancy of Trouton's 

 constant is to be accepted, the latent heat of oxygen should be 

 greater than that of nitrogen — a result in accordance with the above 

 values. 



The latent heat of air will depend on its constitution, tending 

 tx)wards equality with that of oxygen in the case of old liquid air, 

 which is rich in oxygen. In an early experiment, I found the latent 

 heat of air to be 49*7 gramme-calories ; in a later one, it was 53*41. 

 I then made a series of experiments in which a succession of half- 

 grammes of lead, 10 or 12 at a time, were dropped into old liquid 

 air; from these 5:^) -6:^) gramme-calories were found. These values 

 approach those of Fenner and Richtmyer's,* found by an electrical 

 method. 



During the time Professor Curie lectured at the Royal Institu- 

 tion, some measures of a preliminary kind were jointly made by us 

 of the rate at which radium bromide gives out energy at low tem- 

 peratures. The quantity of radium bromide was 0*42 grm. ; and 

 it was used both in a liquid oxygen and liquid hydrogen calorimeter. 

 The thermal evolutions are given below : 



Gas Evolved Calories 



per minute. per hour. 

 Liquid oxygen . . .5*5 c.c. 22 "SI 



Liquid hydrogen . . . 51-0 „ 31 -g} Crystals. 



Melting ice .... — 24*l| 



Liquid oxygen . . . 2-0 ,, 8*3 After fusion. 



Liquid oxygen . . . 2*5 ,, 10-3 Emanation condensed. 



The apparent increase of heat evolution at the temperature of 

 liquid hydrogen was probably due to the calorimeter being too small, 

 so that hydrogen spray was carried away with the gas, thus making 

 the gas volume too great, and inferentially the heat evolved. 



I have to acknowledge the valuable aid I have received from my 

 Chief Assistant, Mr. Robert Lennox, F.C.S., and that of his col- 

 league. Mr. J. W. Heath, F.C.S. 



[J. D.] 



Phys. Rev., 1905, vol. xx. p. 81. 



