THE MOLECULAR THEORY 



329 



In the case of five gases which were soluble in water com- 

 parative experiments were made with tubes of carefully-dried 

 gas inverted over mercury (Fig. 48), the expansion observed 

 being identical in every case with that of atmospheric air. 

 Gay-Lussac summarises his conclusions as follows : 



" The experiments which I have just described and which 

 were all made with great care, prove incontestably that 

 atmospheric air and oxygen, hydrogen, azote, nitrous gas, 

 ammonia, muriatic gas, sulphurous acid, and carbonic acid 

 are expanded equally by 

 the same degrees of heat ; 

 and that, consequently, their 

 greater or less density . . . , 

 their greater or less solu- 

 bility in water and their 

 particular nature, have no 

 influence on their expan- 

 sion." 



" From this consideration 

 I conclude that all gases, 

 in general, are expanded 

 equally by the same degrees 

 of heat ; provided that they 

 are all placed under the 

 same conditions " (loc. cit. 

 p. 172). 



'- 



- i 



" 



- T 



FIG. 48. GAY-LUSSAC'S APPARATUS 

 FOR COMPARING THE EXPANSION OF AIR 

 WITH THAT .OF SOLUBLE GASES AND 

 VAPOURS. 



The gases were confined over mercury 

 in two tubes TT standing in a trough of 

 mercury AC. 



A further series of experi- 

 ments on the expansion of 

 the vapour of ether between 60 and iooC. (loc. cit. p. 173) 

 carried out in the presence of Berthollet, showed that the 

 law of equal expansions could be applied to vapours as well 

 as to gases ; Gay-Lussac therefore concluded that they 

 would probably be equally compressible, i.e. that the simple 

 hypothesis of Boyle could be applied to vapours, so long as 

 they remained uncondensed. All gases and all vapours would 

 then be influenced in the same way by changes of pressure 



