Law of Molecular Attraction. 499 



K MM' 

 Kleeman is trying to apply, namely, /= 5 where M 



and M' are the masses of the attracting particles. 



Prof. D. Tyrer raises an important point * when he says : 

 " We see again that the specific heat o£ a fluid at constant 

 volume increases as the density increases, and from this it 

 must follow that in an isothermal change in density, intra- 

 molecular energy is liberated. This result is of extreme 

 importance in the investigation of the potential energy of 

 liquids and molecular attraction. It vitiates at once all 

 conclusions regarding molecular attraction based on the 

 assumption that during the expansion of a liquid the whole 

 of the energy absorbed goes to do work against molecular 

 attraction, except of course the small amount which does 

 work of expansion against the external pressure." The fact 

 that the specific heat of a gas at constant volume increases 

 as the density increases, and the consequences Prof. Tyrer 

 mentions of this fact, have been long known to me. Never, 

 since my second paper in 1904, have I made the unqualified 

 statement that the total energy of a molecule in the gaseous 

 and in the liquid condition was the same. A distinct 

 statement to the contrary was made in the sixth paper f. 

 Also in a paper on Chemical Energy % attention was called 

 to the fact that there was some energy change which I did 

 not then understand and that the total energy necessary to 

 change a solid monatomic element from — 273° 0. to the 

 liquid condition at its melting-point was about three times 

 the kinetic energy of translation required by the element at 

 that temperature. I may say that in my opinion it is 

 essentially the fact noted by Prof. Tyrer that makes itself 

 felt in various ways. In attempting to find the true equation 

 of state, and in studying surface tension phenomena, as well 

 as when studying specific heats, I continually found that 

 where changes of temperature entered into the phenomena, 

 the relations were not so simple as I had at first supposed. 

 The question was studied from various points of view 

 throughout a period of several years. The true explanation 

 is I think given in my article on Temperature and Molecular 

 Attraction § : 



" The energy given out by any two bodies originally at rest 

 at an infinite distance apart in forming any stable configuration 

 under the action of gravitational attraction is equal to the 



* Phil. Mag. Jan- 1912, p. 112. 



t Jour. Phys. Ohem. xi. p. 156 (1907). 



% Trans. Amer. Electro-chem. Soc xiv. p. 42 (1908). 



§ Phil. Mag. July 1911, p. 97. 



