The Adiabatic Condensation of Ether Vapour 



95 



secured into a mercury chamber by a rubber packed stuffing box^. 

 The chamber is connected by a steel tube to a second chamber containing 

 oil under a screw which can be used to create pressure in the glass tube. 

 The tube has a small amount of ethyl ether on top of the mercury. A 

 small metal box containing coils of nichrome wire surrounds the upper 

 part of the glass tube so that the tube and its contents may be heated 

 to any desired temperature. Since the tube is surrounded by air as the 

 only heating agent, the temperature is not as uniform as might be desired, 

 but the apparatus serves very well. With this apparatus it is easy to 

 bring the temperature to any desired point and then to change the volume 



Fig. 2. 



at will. Among other things it is easy to show the continuous change 

 from liquid to vapour as exhibited by Andrews, a point of which so 

 much was made by van der Waals. 



It is easy to see the effect of adiabatic expansion by plotting the lines 

 of constant dryness on the temperature-entropy diagram and observing 

 how the adiabatics or isentropics cut these lines. We have the necessary 

 data in the results of Regnault for most of the common liquids. The 

 entropy of the vapour calculated from zero Centigrade as the starting 



^Clark, Proc. Am. Acad, of Arts and Sciences. XLI, 371, 1906. 



