HIGH-PKESSURE RESEAECH BRIDGMAN 16] 



As a physicist, I am sanj^uine that the niatheinatician can go far 

 toward reconstructing the function if he knows its first three deriva- 

 tiA^es, and we may hope at any rate that these^ data will make possible 

 a more adequate description of the force field about an atom, even 

 if they do not completely determine the mechanism. 



It has been stated that compressibility becomes less at high pres- 

 sures. This is what we should expect, because, as the atoms are 

 squeezed closer together, it seems natural that they should resist 

 more strongly attempts at closer propinquity. I have found, how- 

 ever, a significant exception in quartz glass and several varieties of 

 ordinary glass in which SiOo is a prominent constituent. These 

 become more compressible at high pressures. This can not but be 

 significant; our theories must explain why it is that, under some 

 conditions, the atoms resist compression less strongly the closer thev 

 are pushed together. It is natural to seek to establish a connection 

 wdth the fact that these abnormal substances are amorphous instead 

 of crystalline, and that they would doubtless crystallize with a 

 decrease of volume. 



The probable effect of pressure on melting temperature w^as for a 

 long time a matter of controversy. Early view^s were strongly influ- 

 enced by the striking critical phenomena between liquid and vapor, 

 and it was supposed by many that there would be found a critical 

 point between liquid and solid such that above this point liquid and 

 solid might be made to change from one into the other without dis- 

 continuity. A later rival theory, strongly defended, was that of 

 Tammann, who supposed that there was a maximum melting tem- 

 perature above which a liquid could not be forced to freeze by any 

 pressure no matter how high, and below which the liquid might be 

 frozen and the solid melted again by a sufficiently high pressure. 

 The experimental difficulty in settling this question was that the 

 available pressure range was not sufficient. But with the data now 

 at hand, we may, I believe, regard this question as settled. It appears 

 from the evidence of 37 substances that there is no experimental rea- 

 son to think that the melting curve does not rise indefinitely, at a 

 continuously decreasing rate, but nevertheless so that at any tem- 

 perature a pressure can be found high enough to freeze the liquid 

 to the solid. There is no connection whatever between the melting 

 phenomena and the ordinary critical phenomena of liquid and vapor ; 

 the amorphous phase may be frozen by sufficient pressure either 

 above or below the critical temperature. This is, after all. the nat- 

 ural result. It would seem as if one ought, by pushing the atoms 

 close enough together, to be able eventually to undo the disorienting 

 effect of an increase in the energy of temperature agitation. A con"^ 

 tinuous passage from a liquid to a solid was most difficult to visualize 

 with our concept of a liquid as a haphazard aggregate of molecules, 



