Force* of Attraction between Atoms and Molecules. 803 



determined for distances less than 100 cm. between the 

 attracting bodies and its value we see is less than that given 

 by the expression for the chemical attraction. The chemical 

 force must therefore decrease much more rapidly than that 

 given by the inverse fifth power law for distarices greater 

 than one centimetre. The result suggests, however, that 

 the chemical force at a distance of one or two cm. from a 

 mass of matter may possibly be comparable with that of 

 gravitation. If that is so, it should not be impossible to 

 detect the fact experimentally. 



To obtain a legitimate comparison between gravitational 

 and chemical attraction it is necessary to compare the at- 

 traction between two molecules separated by a distance 

 equal to their distance of separation in the liquid state, say 

 two molecules of ether at § T c , corresponding to which K 

 has been determined. The distance between two molecules 



of liquid ether at | T? c is ( - 1 J , which gives 5*1 X 10 -8 cut 



The gravitational attraction between two hydrogen atoms 

 separated by that distance is 1*3 XlO -41 dyne, while the 

 chemical attraction is 5'6 x 10~ 10 dyne. The chemical at- 

 traction is thus much greater than that due to gravitation. 

 The gravitational attraction thus plays practically no part iri 

 producing molecular aggregation, and the various phenomena 

 connected with it. 



It will also be interesting to compare the chemical attrac- 

 tion with that of two opposite electrical charges each equal 

 to e. When separated by a distance 10 - " 3 cm. the electrical 

 charges attract one another with a force equal to 1*16 x 10~ 3 

 dyne, while the chemical attraction between two hydrogen 

 molecules for that distance is '2 X 10~ 5 dyne. The electrical 

 attraction is thus greater than the chemical attraction between 

 two hydrogen atoms. But the chemical attraction between 

 two atoms of lead would be about 200 times greater than that 

 between two hydrogen atoms, and thus of the same order of 

 magnitude as the electrical attraction between two charges e. 



The inverse fifth power law of attraction between two 

 molecules has already been put forward by Maxwell. He 

 arrived at the law from the following considerations. 

 Measurements of the coefficient of viscosity have shown that 

 it is proportional to the temperature, and the coefficient of 

 diffusion is proportional to the square of the temperature, 

 but according to the formulas based upon the kinetic theory 

 of gases these quantities vary as the 1/2 and 3/2 power 

 of the temperature respectively. The law of force must 



3F2 



