1906.] 



on Studies on Charcoal and Liquid Air. 



435 



Thermal Conductivity. 



Going to another subject, the well-known experiment of Ingen- 

 housz on the relative conductivities of metals may be repeated at 

 low temperatures by means of liquid air. 



A vacuum-jacketed cup Y (see Fig. 3) is filled with liquid air 

 and covered with a sheet of mica (A B), having a set of small holes 

 in it, through which a series of equal wires of different metals (copper, 

 brass, bismuth, etc.) are fixed. After immersing their lower, ends 

 in the liquid air a coating of frozen moisture is deposited from 

 the surrounding atmosphere, and is seen to collect round the lower 

 parts of the wires above the mica screen, ultimately forming definite 

 heights of an ice cap on each wire according to their conductivities. 

 As in the Ingenhousz experiment, the relative conductivities are 

 proportional to the squares of the heights to which the ice ultimately 

 rises on the wires above the level of the mica sheet. In this 

 manner it is possible to determine rapidly conductivities at low tempera- 

 tures. The following table gives some rough measurements made 

 in this way : — 



A similar method might be employed to determine conductivities 

 at temperatures lower than the melting point of ice ; for instance, the 

 experiment might be made in a dry hydrogen atmosphere containing 

 a small amount of sulphurous acid, continuously renewed, in which 

 case the relative conductivities would be found from the melting point 

 of sulphurous acid instead of from that of ice. 



Gas Absorption ly Charcoal at Loiv Temperatures. 



Some of the more important facts regarding the absorption of 

 gases by charcoal at low temperatures were detailed in the address 

 given in 1905, entitled " New Low Temperature Phenomena," and 

 to those a few additions were made due to further experience. Other 

 porous materials are found to possess the power of absorption for 

 gases at low temperatures to a less extent. Thus dry aluminium 

 oxide shows a remarkable power of absorbing air just like charcoal, one 

 gramme condensing at atmospheric pressure some 70 c.c, and the 



2 F 2 



