Attraction of Mass, and some New Gas Equations. 97 



Substances like Fe and C (diamond) may belong to those 

 which, but for association to complex-molecules, would 

 contain the largest number o£ molecules per unit of volume. 

 Compared with their specificweights, their atomic weights are 

 relatively lowest. It' for these substances all translatory 

 motion ceases, II becomes 0, and 



P = -Pi- 



Instead of exerting pressure, the molecules require a force 

 to separate them equal to the cohesive force of iron, and p± 

 would be the maximum pull iron can oppose before breaking. 

 As J . N . M represents the relative density p in respect 

 of Hydrogen, 1000 c.cm. of iron weigh 7*7 kilogram, of 

 Hydrogen 8*987 . 10" 5 kilogram ; consequently, 

 _ 7-7 



9 ~ 8*987. lO" 5 ' 

 the cohesive force p x per cm. 2 is, roughly, 



p 1 — p 2 . 3 . 10" 6 kilogram (vide eq. 45), 

 and per mm. 2 



p x = ^.S-IO" 8 kilogram. 

 Thus 



* = { 8W1F } ^ 3 * 10 " 8 kil ° gram 

 = 224*1 kilogram. 



This is considerably higher than the pull necessary to break 

 iron. With decrease of diameter the experiment, however, 

 affords rapidly increasing values. Thus a wire of Swedish 

 iron of *72 mm. diameter will stand a pull of 64 kilograms 

 before breaking. But a wire of *10 mm. diameter already 

 requires a pull of 123 kilograms to break it (both, of course, 

 per unit of surface)*. Butp t is the maximum value if all 

 translatory motion has ceased : the wire breaks where it is 

 weakest, the temperature rises during the experiment, and 

 there may remain a degree of translatory movement. 



It is, however, interesting to note that we arrive at a 

 value for the tensile strength of iron which is of the same 

 order as the experimental value, out of the deviations from 

 the gaseous laws. Whatever the ultimate nature of the 

 cohesive forces may be, they seem proportional to the square 

 of the molecular weight, and to obey the inverse square law, 

 — a law consequently similar to Newton's law of attraction 

 of mass. 



Chemical Department, 

 University of Bristol. 



* Poynting and Thomson, 'Properties of Matter/ London, 1915, p. 61. 

 Phil. Mag. S. 6. Vol. 37. No. 217. Jan. 1919. H 



