202 M. J. A. Groshans on the 



Properties of the Substances S 2 C1 2 and S0 2 C1 2 . 



These two bodies have the same molecular weight, the 

 density-number is the same, = 12. The data are as follows: — 



a. B. S°obs. tfobs d . d s . 



S 2 01 2 135 12 1381 173 17094 1-4920 



S0 2 C1 2 135 12 699 120 1*7081 1*5602 



Mean . . a? =1*46. 



The boiling-points differ by 68 0, 2, but the almost perfect 

 equality of the two densities d points to the equality of x\ 

 and we may admit that the true mean value is #=1*5, which 

 gives 110°*1 as the common boiling-point. 



In the two sets of cases that we have examined above, it 

 appears that the disturbing cause does not operate till above 

 0°C., the values of d are the same in each pair. But this is 

 not alwaj'S the case: for instance, in two isomers examined by 

 Thorpe (loc. cit.), 



a. B. S° obs. x obs. d . d s . 



C 2 H 4 C1 2 99 14 835 3*28 1-2808 11563 



C 2 H 4 CJ 2 99 14 599 2-86 12309 11092 



Mean . . a- = 3'07. n/3 = 67'5. 



Such a disturbing influence on the boiling-points and 

 densities of liquids is of a nature to hinder the progress of 

 the study of the physical properties of substances. 



Compounds Liquid at the Ordinary Temperature. 



The best method of applying the law of density-numbers 

 to liquids is perhaps that based, as above, on the comparison 

 of the volumes at the boiling-points ; but the data necessary 

 for this comparison are but seldom available. When this is the 

 case, we are still able in very many cases to verify the density- 

 numbers simply by comparing together the values of d or dt 

 (t being the ordinary temperature 15° — 20°C.) of analogous 

 bodies, when the values of k t will exhibit an agreement more 

 or less complete. 



In Table XXIII. an example is given of the above. The 

 substances are arranged in the order of their boiling-points. 

 By thus employing corresponding temperatures (slightly 

 raised), it is possible to obtain satisfactory concordance in the 

 values of Jc. When £ = the constants k t arrange them- 



