408 WRIGHT and hostetter: crystal growth 



in his discussion of " surfaces of discontinuity between solids 

 and fluids. 4 



While some of the more recent writers on the subject have not 

 discussed the reversibility of the fundamental process, it is in- 

 teresting to note that the reversibility of the process has indeed 

 been questioned by Tammann 5 and by Pockels. 6 Nernst, 7 on 

 the other hand, defended the reversibility of the process and con- 

 sidered that the thermodynamic treatment of such cases may 

 be; carried out exactly. 



Johnston and Adams 8 in their treatment of the effects pro- 

 duced by non-uniform pressure on melting took the position that, 

 inasmuch as the main process may be considered to be made 

 up of an aggregate of reversible local meltings, the process itself 

 may be considered reversible. Niggli, 9 following a line of rea- 

 soning similar to that used by Gibbs, held to the view that, al- 

 though the actual process is not reversible, a comparison of ther- 

 modynamic potentials at the boundary solid-liquid for different 

 states of strain in the solid is permissible. Still another method 

 of avoiding the issue as to the reversibility of the process is that 

 employed by Hassellblatt, 10 namely to consider the process an 

 -"indirect equilibrium." 



EXPERIMENTAL. 



- In the present paper both experimental and geologic field evi- 

 dence are given which prove the correctness of the assumption 

 ■ that the process, even for nonuniform pressure, is reversible and 

 that on crystallization the liquid enters into the crystal state 



under the same state of strain as that of the crystal on which 



- 



it is deposited. This statement is proved by three distinct lines 

 of evidence and is supported by many other facts which have a 



4 Loc. cit., p. 316. 

 ' § Tammann, G. Ann. Phys., (4) 7: 198. 1902. 



6 Pockels, F. Neues Jahrb. f. Min., Centralblatt 1906, p. 667. 



7 Nernst, W. Theoretical Chemistry, 4th ed., p. 667. 



8 Johnston, J. and Adams, L. H. Am. Journ. Sci., 35: 212. 1913. 

 » Niggli, P. Zeit. f. anorg. Chem., 91: 125. 1915. 



10 Hasselblatt, M. Zeit. f. anorg. Chem., 93: 75. 1915. 



