420 ME. T. GEAHAM ON THE ABSOEPTION AND 



hydrogen outwards through the walls of the platinum tube ; and the latter in the end 

 became nearly vacuous from the complete escape of the hydrogen. 



Heated platinum tube containing hydrogen ; air outside. 



the actual height of the atmospheric barometer being 750 millims. at the same time. 

 The tension of the residual gas was therefore no more than 40 millims. of mercury. 

 The ratio between the volume of gas at the beginning and end of the hour is here as 

 18*75 to 1 ; whereas in a diffusion experiment of hydrogen into air, the ratio would be 

 as 3-8 to 1. Further, the residual gas in the platinum tube still retained a small por- 

 tion of hydrogen. Withdrawn by means of the Sprengel pump and examined, the resi- 

 dual gas in the platinum tube amounted to 3-56 cub. centims., and consisted of 



Nitrogen 3-22 cub. centims. 



Hydrogen 0-34 „ 



3^ 



The available capacity of the platinum tube was 113-1 cub. centims. ; and when the 

 tube was heated, the gas driven out by dilatation measured in the cold 39-5 cub. cen- 

 tims., leaving in the hot platinum tube 73*6 cub. centims. of gas estimated at 20° C. 

 and barom. 760 millims. It was found necessary in these experiments to stuff that 

 portion of the platinum tube that was placed across the furnace and strongly heated, 

 with asbestos, to give support to the tube when softened by the heat of ignition, and 

 to prevent the tube from collapsing. 



It is difficult to say where the small volume of nitrogen found in the platinum tube, 

 amounting to 3*22 cub. centims., actually came from. It appears too great in amount 

 to have formed an impurity in the original hydrogen gas, or to have gained access to 

 the vacuum through defective joinings in the apparatus. Its presence suggests the 

 inquiry, admitting that nitrogen cannot pass alone through platinum into a vacuum, 

 whether the same gas may not be enabled to pass, in some small proportion, while 

 hydrogen is simultaneously travelling through the platinum in the opposite direction. 

 The liquid or the gaseous hydrogen occupying the platinum septum would thus form a 

 vehicle or channel, by the help of which another analogous body like nitrogen might 

 be conceived capable of passing through the platinum in small quantity, by a process of 

 liquid or gaseous diffusion. 



