518 



Drs. Ramsay and Young on 



Another method of comparison is to regard the value of 

 for water as equal to unity at each pressure, when the 



numbers for chloroform become 



1-00 0-962 0-953 0-938 0922 0-911 0-903 0-893 0-885 0*850. 



Similar results may be obtained on comparing other bodies 

 with water; it may be, however, remarked that the instance 

 chosen is one of those in which least concordance is to be 

 noticed. It is evident that here also the concordance is 

 merely approximate. 



Another point worthy of notice is this. The heat of 

 vaporization is expended in at least two channels : — it pro- 

 duces expansion against pressure, thus doing external work ; 

 and it is partly expended in internal work on the molecules 

 of the body. Now it follows from what has preceded that 

 the internal and total work bear an approximately constant 

 proportion to each other for any one pressure, whatever be 

 the liquid. Thus at a pressure of approximately 760 millims. 

 the ratio of external to total work is shown as follows : — 



Substance. 



Total work. 



External work. 



Bromine 11-09 



Phosphorus chloride ... 10*09 



Carbon disulphide 10*39 



Methyl alcohol 12*53 



Ethyl alcohol 13*33 



*Ethyl oxide (ether) 1 1 55 



Water 1302 



Methyl iodide 10*45 



Ethyl iodide 10*69 



Methyl formate 11*55 



Methyl acetate 12-51 



Substance. 



Total work. 



External work. 



Ethyl acetate 11-81 



Ethyl oxalate 11-67 



Amyl alcohol 13*32 



Ethyl chloride 11-39 



Benzene 10*25 



Chloroform 10*99 



Carbon tetrachloride ... 10-35 



Mercury 12*36 



^Nitric peroxide 12-42 



Acetic acid 13*18 



Water 13*02 



* Vapour-density found at a few degrees above boiling-point. 



In the equation- =.-¥• — , both terms are approxi- 



s 1 — s 2 at o xx 



mately known for a number of substances. But before com- 

 paring them it is necessary to reduce the pressures which 

 have been given in the previous part of this paper in milli- 

 metres of mercury, to grams per square centimetre. The 

 comparison has been made for water, with the following 

 results : — 



