164 Intelligence and Miscellaneous Articles. 



and immersed in an oil-bath. After being heated to a given tempe- 

 rature, it is exhausted and the liquid gradually introduced. The 

 moment of saturation is ascertained by a slight deposit of dew on 

 the glass plates. Connexion is then established with a cold reser- 

 voir containing air at a known pressure, lower than that of the 

 vapour ; and at the same time the condition of the cylinder is ob- 

 served. 



Water and ether behaved as in the experiments of M. Hirn ; the 

 vapour of the latter liquid never condensed by expansion, while that 

 of the former always did. When the difference of pressure was 

 more than 0'5 metre of mercury, the fog formed rendered the interior 

 of the cylinder completely opake ; when it was less, a halo was often 

 seen round a flame looked at through the vapour. 



With chloroform, the inversion takes place when the pressure of 

 the reservoir is increased. Beyond a certain pressure no condensation 

 is obtained, even when the excess of the pressure of vapour is mate- 

 rially increased. An idea of the experiments may be formed from the 

 following Table, in which the pressures are approximately measured 

 by columns of mercury. 



D ressure in the 



Excess of pressure 



Temperature 



Effect 



air-reservoir. 



of the vapour. 



of the vapour. 



observed. 



metres. 



metres. 







0-75 



0-90 



85 



Condensation. 



075 



1-09 



89 



>> 



0-75 



1-62 



99 



»> 



1-47 



0-92 



99 



>t 



1-47 



2-18 



117 



>> 



1-84 



2-01 



119 



*» 



225 



2-52 



129 



>» 



3-27 



1-13 



125 



No condensation 



3-50 



WO 



127 



>» 



3-94 



2-50 



143 



*i 



4-01 



2-64 



145 





It is thus seen that vapour saturated at 125° and expanding with 

 an excess of pressure of 1*13 metre does not condense, but that 

 vapour at 129° condenses with an excess of 252 metres. It is 

 readily understood that this latter, attaining during expansion the 

 temperature of inversion at the moment at which it has a pressure 

 equal to the maximum tension which corresponds to this tempera- 

 ture, behaves from this moment like a vapour which starts from a 

 temperature lower than that of inversion ; thus in this case the fog 

 is only visible at the end of the expansion. — Comptes Rendus, Janu- 

 ary 2, 1866. 



, 



