252 



Prof. J. Dewar. 



[Mar. 9, 



glass bulb was immersed in liquid oxygen, nitrogen, or hydrogen 

 contained in a vacuum-jacketed vessel with arrangements for lowering 

 the temperature of the liquids by exhaustion. The narrow tribe just 

 above the glass bulb had a mark engraved upon it, and the volume 

 up to this point, which is to be filled with liquid or solid after cooling, 

 was antecedently carefully calibrated. The glass stop-cock on the 

 projecting part of the glass tube outside the vacuum vessel enabled 

 the rate of the gas supply to be under complete control. The real 

 difficulties were those of manipulation. 



The temperatures employed were the boiling point of oxygen, 

 90°'5 ; the boiling point of nitrogen, 77°*5 • the melting point of 

 nitrogen, 62°*5 ; the boiling point of hydrogen, 20°*5 ; hydrogen boiling 

 under 76 mm. of pressure taken as 14°*7 ; and hydrogen (solid) under 

 10 mm. of pressure taken as 13°*1. 



Allowance for the contraction of the bulb was made by taking 

 0*0000250 as the coefficient of contraction (cubical) of the glass. It 

 is possible that in going to very low temperatures (below -200° C), 

 this coefficient ought to be less, such as 0*0000225. An estimate made 

 of the difference between the two would come within the range of 

 errors, consequently the former value which was adopted in the earlier 

 investigations was retained. 



The weight of 1 litre of oxygen at 0° C. under 760 mm. pressure 

 was taken as 1*430 grammes, of nitrogen as 1*2564 grammes, and of 

 hydrogen as 0*0899 gramme. 



The observations and results are given in the following tables : — 



Table I. — Oxygen. 



No. 



Description. 



T'. 



V. 



T. 



P- 



d. 













mm. 





1 



At B.P. of O .. 



-182° 5 



19 -631 



14 4 



758-5 



1 *1181 



2 



At B.P. of N.. 



-195 *5 



20 536 



14 *4 



758-5 



1 *1700 



3 



At M.P. of ~N. . 



-210 5 



21 -743 



14*55 



758*5 



1 2386 



4 



At B.P. of H .. 



-252-5 



25 003 



14*6 



758 *5 



1 *4256« 









(solid) 









Where T' = the temperature Centigrade of the condensed gas in the 

 flask at the time of observation. 

 V = volume of gas in litres at temperature T° C. and pressure 

 p. mm. 



d = density of the condensed gas at T'° C. 



The volume. of the flask at 15° C. was 23*9212 c.c. 

 Coefficient of expansion of glass, taken as 0*0000250. 

 Weight of 1 litre of oxygen at 0° C. and 760 mm., taken as 1*430 

 grammes. 



