THE ADIABATIC CONDENSATION OF ETHER VAPOUR 

 By A. L. Clark, Ph.D., F.R.S.C. 



Read May Meeting, 1920. 



It is a well known fact that water vapour under certain conditions 

 condenses when expanded adiabatically. If the water vapour in the 

 air is approximately near the saturation point, an adiabatic expansion 

 will bring about condensation, which is greatly facilitated by the presence 

 of nuclei in the air. No doubt almost all cloud formation is due to adia- 

 batic condensation of moisture laden air. Conversely the adiabatic 

 compression of a fog bearing body of air will bring about evaporation of 

 the cloud if the compression is sufficiently great. We find evidence of 

 both phenomena in the well known alto-wave cloud formation, or in 

 the common cirrocumuli of "mackerel sky." The visible portions are 

 the crests of waves where the expansion accompanying increase in 

 altitude has brought about cloudy condensation, while the blank spaces 

 are the troughs of the waves where compression accompanying rapid 

 descent has evaporated the cloud or has prevented its formation. 



The condensation mentioned is, of course, independent of the presence 

 of air and takes place equally well in a closed tube where only water and 

 water vapour are present. The same is true of the vapours of other 

 liquids, indeed nearly all, in fact of all except a very few, notably ethyl 

 ether whose saturated vapour has a positive specific heat at ordinary 

 temperature. That the vapour of water should condense upon adiabatic 



^60 



I. Water. 



2. Carbon Bisulphide 



6. Chloroform 



Fig. 1. 



3. Acetone. 4. Carbon Tetrachloride. 

 7. Ethyl Ether. 



93 



5. Benzine. 



