GENERAL CHEMISTRY OF THE PROTEINS 7 



applying the laws of mechanics. For a gram molecule of a gas 

 (or dissolved substance) the simple formula of the kinetic theory 

 reads : 



pv = 2 N^ = RT, 



where N is Avogadro's number and w the mean kinetic energy 

 of one molecule of gas or solute. 



The kinetic theory of gases has, moreover, caused the 

 behaviour of gases under high pressure to be compared with 

 that of liquids, with the result that the apparent difference in 

 molecular condition in the two cases is not found to exist.* 



J. Perrin f has applied the conclusions of Van t'Hoff for 

 solutions to the cases both of pure liquids and of suspensions. 

 To quote his own clear summary : " Van t'Hoff 's law states 

 that a molecule of ethyl alcohol has the same energy in an 

 aqueous solution as when it is vaporised therefrom. It would 

 also possess the same energy in solution in chloroform, that is, 

 when surrounded by chloroform molecules, and similarly in 

 solution in methyl or propyl alcohol. It may therefore be 

 supposed that its energy is also the same in ethyl alcohol solu- 

 tion ; in other words, when it is a constituent molecule of pure 

 ethyl alcohol. So that, by admitting that the molecular energy 

 is the same in the liquid as in the gaseous state, we can now 

 state that at the same temperature the mean kinetic energy of 

 all molecules of every liquid is the same, and is proportional to 

 the absolute temperature. 



" The general hypothesis can, however, be still further deve- 

 loped. From what has been stated above, the heavy sugar 

 molecules in a sugar solution have the same mean energy as the 

 mobile molecules of water. Now the sugar molecule contains 

 45 atoms ; that of quinine sulphate more than 100. One 

 can enumerate still heavier and more complex molecules, to all 

 of which the law of Van t'Hoff is applicable, for no limit is 

 placed to the size of the molecule. Consider, now, a particle 

 made up of several molecules, say a dust particle. Is it likely 

 it will conform to a different law under the bombardment of the 



* See W. Nernst, " Theor. Chemie.," 1907, p. 226. 



\ See Koll. Chem. Beihefte, 1910, 1, 221, for complete literature. 



