1 



I 



354 PROCEEDINGS OF THE AMERICAN ACADEMY § I 



according to Gay-Lussac, by from 600* to 5000 dynes.f ; 



The expansion into vapor being nearly equal to 1630 vol- 1 



umes of the boiling liquid shows that the cohesive attrac- i 



tion must have diminished between seven million and \ 



seventy million times, while the distance from particle to i 



particle must have increased in the ratio of the cube ! 



root of 1630, or 11.75. ^^^ this case, therefore, we might I 



infer that the cohesive attraction per unit of surface varied • 



inversely as some power of the molecular distance not ' 

 less than six and not greater than seven and one-half, a 



mean value being the most probable; and remembering J 

 that the number of particles which exert this attraction 



diminishes as the square of the distance increases, the i 



molecular attraction would vary according to the fourth j 



or fifth power, inversely. % 



For alcohol, in the same way, the coefficient of expan- ; 



sion at 78° being .0013, the total expansion into vapor about ' 

 455 volumes, and the difference of specific heats, 15,000,000 



ergs, the cohesion is about 12,000,000,000 dynes per I 



square centimetre, and since the pressure of the saturated | 



vapor according to Gay-Lussac,J reduced by suitable ] 



formulae, is 15,000 dynes less than the theoretical value, I 



it would appear that the molecular attraction varied as i 



the four-and-two-thirds power, inversel}'. i 



For ether we find a difference of specific heats of only 



4,000,000 ergs, and a coefficient of expansion .0017, in- ' 



dicating about 2,400,000,000 d3'nes for the cohesion; the ' 



expansion into vapor is about 235 volumes, and the pres- | 



sure of cohesion of the vapor, deduced from Gay-Lussac's i 



figures, § is 14,000 dynes, also indicating the four-and- | 



two-thirds power of the distance. i 



These are the only liquids which I can find, the density 1 



* Allowing for the space occupied by the molecules. See Zeuner, Chap. I, III, Chaleurs 

 lafentes interne et externe. 



t See Deschanel's Natural Philosophy, Part II. (283-284. 

 J See Zeuner, French Translation, 1869, page 282. 

 § Zeuner, ibid. 



