8 



Messrs. Barrel^ Thomas, and Young on tlie 



Again, the ratios of the actual to the theoretical density 

 (for a perfect gas) at the critical point should be the same 

 for all substances if Van der Waals's generalizations were 

 strictly true : these ratios are also given in the table under 



the heading ^y- 





PV 



T) 



Substance. 



"T" 



D 7 ' 





. 16390 



3-79 





. 16380 



3-77 





. 16270 



3*80 





. 16360 



3-78 





. 16610 



3-71 



Carbon tetrachloride.. 



. 16940 



3-65 





. 16630 



376 





. 16290 



3-83 



Methyl alcohol 13750 4-52 



Ethyl alcohol 15470 4-02 



Propyl alcohol 15460 4-02 



Substance. 



PV 



D 





T 



JJ' 





12440 



500. 





. 15840 



393 





. 15990 



3-88 





. 15750 



394 





.. 16070 



387 





.. 15730 



3-95 



Methyl propionate . 



. 15920 



390 





. 15760 



3-94 





. 15830 



3-92 





. 15900 



3-90 



Methyl isobutyrate . 



.. 16070 



3-87 



Here, again, the grouping of the compounds is well 



py 



marked : acetic acid has by far the lowest value of -™- (and 



the highest density ratio) ; the alcohols come next in order, 

 the values for methyl alcohol standing about midway between 

 those for the other alcohols and acetic acid ; the esters 



PV 



agree well together, the values of -_- being in every case 



lower than for the members of the first group. 



II. On the Separation of Three Liquids by Fractional Dis- 

 tillation. By Professor F. R. Bakkell, M.A., B.Sc, 

 G. L. Thomas, B.Sc, and Professor Sydney Young, 

 B.Sc, F.R.S., University College, Bristol*. 



IT is well known that the separation by fractional distillation 

 of two substances which are miscible in all proportions 

 and which do not — like propyl alcohol and water or formic 

 acid and water — form mixtures of constant boiling-point, is 

 usually a simple matter if there is a considerable difference 

 in their boiling-points. The facility with which the sepa- 

 ration can be effected depends, in fact, chiefly on this 

 difference. 



* Communicated by the Physical Society : read November 10, 1893. 



