REVIEWS 3 21 



are they chemically. This last fact may partially explain the occur- , 

 rence of chemically active substances uncombined deep within the 

 earth. It is to be noted, however, that temperature acts in an oppo- 

 site sense to pressure and for every allotropic state there may be a 

 critical temperature above which it cannot exist no matter under what 

 pressure. 



In several following papers he explains experiments which confirm 

 his previous conclusions on the diffusion of matter in the solid state. 

 He finds that the velocity of diffusion depends upon three factors: (i) 

 a constant peculiar to each substance and depending upon the velocity 

 of molecular movements ; ( 2) the temperature, with which the molecular 

 velocity increases, and (3) the pressure, which makes the contact more 

 perfect and tends to overcome the " surface tension " of the solid par- 

 ticles. He demonstrates that there is a critical temperature for the 

 change of solids into liquids and mentions cases where liquids by 

 increase of pressure have been changed into solids. 1 



In further experiments he finds that intimate contact caused by 

 constant shaking without pressure causes diffusion between solids, and 

 this diffusion takes place with extraordinary rapidity (three hours) at 

 a higher temperature, though far below the melting point of either 

 substance employed. 2 



In the article " Sur l'apparition dans l'etat solide des certaines pro- 

 prietes caracteristiques de l'etat liquide ou gazeux des metaux," 3 he 

 recapitulates some of his former conclusions and presents new ones as 

 follows : 



1. Cohesion between fragments like that between drops of water 

 must be overcome before diffusion between the two can take place. 



2. The property of diffusion under pressure is not equally devel- 

 oped in all bodies and is best developed where internal friction is the 

 least and where molecular velocity is the greatest. 



1 Reaction du sulfate de baryum et du carbonate de sodium sous l'influence de 

 la pression. Bull, de 1'Academie, etc. 3 me sdrie, 10, 1885, p. 204. 



Bull, de la Socie'te chimique de Paris, XLI, p. 488. 



Sur un case de decomposition chimique produite par la pression. Bull, de 

 'Academie, etc. 3 me serie, 13, 1887, p. 409. 

 Zeits. f. Phys. Chemie. I, p. 165. 

 Comptes rendus, t. CV, 1887, p. 165. 



2 Sur la reaction chimique des corps a l'etat solide. 3 me se"rie, 16, 1888, p. 43. 

 s Bull, de 1' Academie, etc. 3 me sdrie, 28, 1894, p. 23. 



Zeit. f. Phys. Chemie. 



