94 tutton: x-ray analysis and assignment of crystals 



and circulation of liquid continued, but here again, instead of 

 deposition taking place on the remaining crystal, other nuclei 

 were formed developing later into the usual fernlike growths. 

 These experiments were repeated under a sufficient variety of 

 controlled conditions to show that the phenomenon was con- 

 nected with certain relations at present beyond our control. 



The literature is filled with observations on the effect of 

 foreign material on crystal habit but experience gathered in the 

 course of these investigations has shown that, in general, such 

 effects have been largely overestimated, at any rate in certain 

 classes of salts. Furthermore, it will be shown in future publica- 

 tions that there is nothing mysterious about the action of addi- 

 tion products in many cases, but that a simple explanation based 

 on well-known physico-chemical laws will suffice. 



The crystals grown in this apparatus have been used in the 

 study of certain problems connected with the linear force of 

 growing crystals,^" and also the effects of nonuniform pressure 

 on solubility. ^^ The publication of other results, delayed by the 

 war activities of this Laboratory, will be made as opportunity 

 permits. 



CRYSTALLOGRAPHY.— X-fa>; analysis and the assignment 

 oj crystals to symmetry classes. Alfred E. H. Tutton, 

 Past President of the Mineralogical Society of London. 

 (Communicated by R. B. Sosman.) 



A memoir on the above subject is contributed by Edgar T. 

 Wherry to a recent issue of this Journal^ which calls especially 

 for some notice, inasmuch as it is largely based on certain mis- 

 conceptions regarding fundamental crystallographic facts, of 

 a type which is becoming increasingly common among the 

 growing number of workers and writers on this new and highly 

 inviting subject of X-rays and crystals. The memoir in question 

 assumes that evidence has been accumulating that the crystals of 



1" Becker, G. F., and Day, A. L. Journ. Geol. 24: S'^iSSS- 1916. 

 " HosTETTER, J. C. Journ. Wash. Acad. Sci. 7:79. 1917. Wright, F. E., 

 and HosTETTER, J. C. Op. cit. 7: 405. 191 7. 



1 This Journal 8: 480. 1918. Compare also Dr. Wherry's reply, p. 99. 



