336 "Prof. Magnus on the Condensation of Gases 



metres, hence the condensation for every such square is 



196k = 000080 °- 



For the unit of the smooth surface of glass, the condensation of 

 sulphurous acid at 0° is therefore =0*0008 of the unit of volume. 



This calculation is based on the assumption that the conden- 

 sation at 100° is a vanishing quantity. If at this temperature 

 a condensation still exists, which might be ascertained by com- 

 paring the expansion of the gas in the two tubes at higb tem- 

 peratures, then the condensation at 0° would amount to more 

 than 00008 of the unit of volume. 



It remains to determine the condensation of other gases in a 

 similar manner ; this is the more necessary, as the experiments 

 of MM. Jamin and Bertrand, so far as they have been made 

 known, have been confined to the condensation effected by 

 bodies in powder. 



Having found the amount of the condensation upon smooth 

 surfaces, it appeared of interest to ascertain whether it is much 

 greater upon rough surfaces. 



Determinations of the coefficients of expansion were therefore 

 undertaken where spongy platinum was made use of instead of 

 glass. To enable us to judge of the purity of the gas in 

 these experiments also, a tube was filled which contained no 

 platinum, while another contained 7 grammes of the substance. 

 Both tubes had nearly the same volume as the former ones, and 

 were filled at the same time. In order to be certain that no 

 sulphuric acid was formed by the presence of the platinum and 

 atmospheric air, the tubes were first filled with hydrogen, the 

 spongy platinum being heated to redness by a lamp. The air 

 and water being thus completely expelled, the sulphurous acid 

 was conducted through both tubes, until on its escape it was 

 completely absorbed by caustic potash; the tubes were then 

 cooled, hermetically sealed, and fixed in the two pieces of appa- 

 ratus above mentioned. 



The determination of the coefficient of expansion gave the 

 following result : 



In the tube. 



Without spongy platinum. With spongy platinum. 



0-3822 03922 



from which we obtain 



- =0-00G5. 

 n 



As the content of the tubes was the same as the tubes with the 



