Law of Density-Numbers. 201 



In this connection I shall take some other case from the 

 paper by Thorpe on the molecular volumes of liquids, Chem. 

 Boo. Journ. 1880. 



Properties of the Compounds Br 2 and IC1. 



The molecular weights of the above substances are respec- 

 tively 160, 162*5, being very nearly equal, and both have 

 B = 18. We would expect to find their densities (at the boil- 

 ing-points) equal, but they differ by 0*1, or about 3*5 per 

 cent. With regard to their densities at C C, S , these are 

 practically equal, notwithstanding the fact that their boiling- 

 points differ by 42°. The following are the data relating to 

 the above : — 



Br 2 

 IC1 



a. 

 160 



162-5 



B. 



18 



18 



S°. 

 593 



101-5 



x. 

 1-81 



2-22 



3-1883 

 3-1822 



2-9822 

 2-8812 



The values of x differ from the whole number 2 : the one is 

 smaller, the other greater, the mean being # = 2'01. Where 

 .£ = 2 for each body the respective boiling-points would be 

 76 c, 5 and 81 c, 9, which lie close together ; and the two densi- 

 ties d 8 and d f s i would have been equal. I have calculated from 

 the dilatations observed by Thorpe, what the densities would 

 be at the calculated boiling-points : they are respectively 

 2-9244 and 2-9404. 



It appears, then, that there exist in the case of these sub- 

 stances certain unknown causes which affect the boiling- 

 points, raising the one 19 0, 4 and lowering the other 17°*5. 



The existence of such an influence in very many cases will 

 be strange to no one, for it has been suspected by many. It 

 is the new Law, however, that points most clearly to it. 



This also explains why the values of w, calculated from 

 observed boiling-points, do not always present themselves as 

 whole numbers, but are often affected by fractions, for 

 instance : — 



I have for valid reasons assumed that # = 3 in the case of 

 the four following bodies (see above) : — 



C 2 H 6 S 



C 2 H 6 Se . 



*=3-05. 



C 2 H 6 S 2 

 C 2 H 6 Te 



a=f312. 



# = 3-27. 



The 



experiments of Thorpe (loc. cit.) furnish jet another 

 example. 



