Properties of Liquid Mixtures. 47 



pressure by y \jo (temperature constant) would needa change 

 usually as great as ^ or more in the composition; this 

 would correspond to about ±' of arc on the refractometer — a 

 quantity very easily observed. The composition of the 

 mixture might alter by escape of the vapour past the con- 

 denser; this would be discovered by a comparison of the 

 refractive index before and after the boiling— as a matter of 

 fact, the change rarely exceeded 2': further, it would neces- 

 sarily alter as some of the substance was present in the form 

 of vapour, but the weight of vapour in the apparatus could not 

 have exceeded -^-^ of the weight of liquid, and as the com- 

 position of the vapour is never 30 per cent, different from that 

 of the liquid, the evaporation of that quantity could not alter 

 the composition of the remainder more than about g 1 ^. The 

 degree of accuracy thus anticipated appears to have been 

 realized except in a few unfavourable cases, as will be seen 

 from the following observation, which is given as a spe- 

 cimen, and to show the mode of reduction adopted. 



Specimen Observation. 

 Weighing-bottle 11*3608 grms.) 

 + toluene . . 17-1159 „ [ 52*40 per cent, of CC1 4 . 



+ CCI 



23-4510 



Refractometer before 40° 16£' at 21°'l. Hence /x 18 = 1-48817, 

 after 40° 20V at 21°'8. „ = 1-48809. 



Height of 

















Pressure. 



Obs. 

 temp. 



Oorr. 



temp. 



Log 

 pressure. 



L og_P 5 o- 







Barom. 



Gauge. 













7791 



6145 



1646 



48-14 



48-20 



2-2164 



22470 



(779-4) 



596-8 



182-6 



50-84 



5092 



•2615 



59 



(7796) 



580-5 



199-1 



53-18 



53-31 



•2991 



27 



779-9 



561-3 



218-6 



55-60 



55-79 



•3397 



12 



(779-6) 



587-4 



192-2 



52-24 



52-33 



•2838 



42 



(7794) 



608-0 



171-4 



49-38 



49 45 



•2340 



32 



(779-2) 



625-3 



153-9 



46-64 



4669 



•1872 



36 



7791 



641-4 



137-7 



43-90 



43-93 



•1389 

 Mean= 



22 

 2-2437 



From curve v °' ' 

 dt 



:0-01702. 



The observed temperatures and logarithms of the pressure 

 were, in practice, plotted on a curve (which was approxi- 

 mately a straight line), and the values of log^ 50 and d(\ogp)/dt 

 read off. Here the values of log p 50 have been calculated 

 from each observation and the assumed temperature-coefficient, 

 in order to show the degree of concordance obtained The pro- 



