4 Prof. Magnus on the Propagation of Heat in Gases. 



offers a greater hindrance to motion in other gases than in hy- 

 drogen, still this hindrance is in any case so small as not to 

 cancel the influences of the greater expansibility of other gases, 

 such as carbonic acid or sulphurous acid. 



But if the expansion in hydrogen can produce no stronger 

 currents than in other gases, there remains no other assumption 

 to explain the more rapid cooling in it than that this gas can 

 conduct heat — that is, can give it from particle to particle, as is 

 the case with metals — and that it possesses this property in a 

 higher degree than other gases. The small density of hydrogen 

 militates against this assumption ; and it appeared necessary to 

 decide by a few experiments how far it was correct. Accord- 

 ingly in a glass tube 2 centims. broad and 10 centims. long, and 

 closed at one end, a thermometer was fitted air-tight, so that the 

 bulb was in the middle of the tube, while the graduation was 

 above the cork. In order to fill the tube with different gases, 

 there were two narrow glass tubes fitted into holes near the 

 thermometer. Outside the tube they were bent at right angles, 

 and could be closed by stopcocks. After water had been boiled 

 in a capacious flask until all air had been expelled, the tube 

 which had been previously filled with gas, was introduced into 

 the flask, during the ebullition, in such a manner that it was 

 entirely surrounded by vapour. The time was then measured 

 which elapsed before the thermometer rose from 20° to 80° C. 

 or 90° C. 



The following results were obtained for the time necessary to 

 heat the thermometer in the different gases : — 



In 



20° to 80°. 



20° to 90°. 



Atmospheric air 



. 35 minutes. 



5-25 minutes. 





3-5 



>■> 



5-25 



)> 





35 



)> 



5-2 



>> 



Hydrogen . . 



. 1-0 

 10 



)) 



1-5 

 1-25 



» 





1-1 



a 



1-4 



>) 





1-0 





1-5 



)) 



Carbonic acid . 



. 4-25 



)> 



65 



}j 





4-25 



}} 



6-25 



>t 



Ammonia . . 



. 3-5 



>) 



5-5 



)> 





3-5 



„ 



5-5 



)) 





3-5 



„ 



5-25 







35 





5-25 



j) 



Analogous experiments have been made by Leslie*, Daltonf, 



* Inquiry into the Nature of Heat, p. 483. 



f Memoirs of the Manchester Literary and Philosophical Society, vol. v. 

 part 2. p. 379. 



