PROCEEDINGS 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. VII, pp. 2S3-3SS. July 24, 1905. 



THE LINEAR FORCE OF GROWING CRYSTALS. 

 By George F. Becker and Arthur L. Day. 



That growing crystals exert a linear pressure in the direc- 

 tion in which they grow appears to have been first observed by 

 Dr. Jean Lavalle in 1853.^ He noticed that crystals in satu- 

 rated solutions increase most rapidly on their under surfaces, so 

 that the first portion of the crystal to form is driven upward by 

 the forces involved in the crystallization. This result was de- 

 nied by Kopp, but has since been confirmed by various authori- 

 ties, including Lehmann, who gave an account of the matter in 

 his work on Molecular Physics" in 1888. The evidence in 

 favor of Lavalle's view includes many familiar phenomena like 

 the raising of crusts of earth by frost, the appearance of which 

 must be familiar to everyone in high latitudes. Perhaps a 

 still better one, to which reference has not been made, is the 

 fact that fence-posts are very apt to be gradually drawn out of 

 their beds by recurrent frosts. 



No quantitative experiments have been made, so far as we 

 know, on this subject, which seems to have excited very little 

 attention for the past twenty years. 



In the study of ore deposits, occurrences are sometimes ob- 

 servable in which crystals have exerted a very considerable 

 force ; for example, it was long ago noticed that crystals of 

 pyrite form in slates in such a way as to drive apart the lamince 

 of the rock without any sensible or traceable deformation of the 

 crystals.^ More important evidence of similar action is found 



' Compt. Rend., vol. 36, 1S53, p. 493. 

 2 Vol. I, p. 345. 



3U. S. Geol. Survey, i6th Ann. Rep., Part III, p. 2S7. 

 Proc. Wash. Acad. Sci., July, 1905. 



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