320 REVIEWS 



besides his own valuable results, an excellent resume of all the differ- 

 ent theories concerning regelation. From experiments upon all kinds 

 of chemical compounds he develops the following : 



i. All solid bodies tend to consolidate under pressure, and this 

 tendency is a function of the malleability of the substance or, in other 

 words, an inverse function of the internal friction. 



2. Pressure aids in consolidating or welding solid bodies because 

 it makes an intimate contact. 



3. Bodies capable of assuming crystalline form tend, under pressure, 

 to weld so that the mass has a single crystallographic orientation. 



4. Welding under pressure is caused by an actual molecular dif- 

 fusion in the solid state similar to that in liquids, but far less active. 



5. Pressure aids diffusion merely by bringing the particles into 

 intimate contact with each other. 



6. The reactions of solids upon solids are equilibrium reactions, 

 and therefore chemical action under pressure tends to go in the direc- 

 tion which gives the smaller volume. Therefore, since the crystalline 

 state is generally that which takes the smallest volume, pressure aids 

 crystallization. 



In two succeeding articles he states that solids, as well as liquids 1 

 and gases, are perfectly elastic volumetrically, that is, upon removal of 

 pressure, the molecules vibrate with the same frequency as before and 

 so the substance assumes its former volume. The only compression he 

 could produce was caused by the crushing in of cavities, etc., and large 

 contraction only occurred where new chemical compounds were formed, 

 as where a new allotropic or polymeric form of the substance was 

 assumed. The statement that matter takes an allotropic state corre- 

 sponding to the volume which it is obliged to occupy has an exact 

 significance. Moreover, the different states of matter all belong to 

 one series — a liquid is an allotropic form of a gas — a solid of a liquid 

 — a denser solid of a solid of less specific gravity. 



This polymerization of molecules accounts for all changes of form 

 and the more dense the polymeric forms, in every case the less active 



la pression. Bulletins de l'Academie Royale de Belgique. 2 me serie, 49, ]88o, 

 P- 323- 



1 Formation de sulphures metalliques sous Taction de la pression. 3 me serie, 5, 

 1883, p. 492. 



Sur l'elasticite parfaite des corps solides chimiquement definis. Analogie nouvelle 

 entre les solides, les liquides et les gaz. 3 me serie, 6, 1883, p. 507. 



