532 S. Taker— Growth of Crystals, 



Art. XXXYII. — The Growth of Crystals Under External 

 Pressure ; by Stephen Taber. 



The question whether it is possible for growing crystals to 

 exert a linear pressure is of such great interest and importance 

 to geologists that it is surprising the problem has received so 

 little attention. Jean Lavalle, in 1853, appears to have been 

 the first to assert that crystals do exert such a force.* He 

 observed that crystals were pushed upward during their growth. 

 This, however, was denied by Kopp, who, upon placing crys- 

 tals of alum colored with a small amount of chrome alum in a 

 solution of plain alum and allowing them to grow, noticed that 

 no material was deposited on the under side of the colored 

 crystals. He states that he was never able to observe anything 

 tending to confirm the view that a crystal can raise itself in 

 order to grow also on the side on which it rests.f Since that 

 time several investigators have published their conclusions but 

 they have reached no general agreement. It is not necessary 

 to review here the literature bearing on the subject, a very 

 complete bibliography of which has already b&en published by 

 Dr. E. Andree4 



In 1905 Becker and Day published an account of their very 

 interesting and suggestive experiments. § Using alum, they 

 found it possible "in a saturated solution of constant temper- 

 ature to grow clear crystals a centimeter in diameter which 

 would raise a weight of a kilogram through a distance of sev- 

 eral tenths of a millimeter. The crystal was placed upon a 

 piece of plate glass in a beaker containing saturated solution of 

 the same material, and loaded as desired. Knowing the weight 

 raised, it appeared an exceedingly simple matter to determine 

 the force required, since it was only necessary to ascertain the 

 actual area of contact between the weight and the crystal. 

 Here, however, an unexpected difficulty was encountered."! 

 The under side of the crystal where it rests on the plate glass, 

 instead of being plane consists of a terraced cavity so that the 

 bearing surface is only a narrow rim around the outer edge of 

 the crystal. The exact measurement of this area of contact is 

 very difficult and uncertain, and, therefore, it is hard to esti- 

 mate the force per unit area exerted by the crystal. However, 



*Compt. Rend., vol. xxxvi, p. 493, 1853. 



fKopp, H., Uber die Bildung von Krystallen mit Kernen, Ann. Chem. 

 Pharni., vol. xciv, p. 124, 1855. 



% Die geologiche Bedeutung des Wachstuinsdrucks kristallisierender Sub- 

 stanzen, Geologische Rundschau, vol. iii, pp. 7-15, 1912. 



§ Becker, G. F., and Day, A. L. , The Linear Force of Growing Crystals, 

 Proc. Washington Academy of Sciences, vol. vii, pp. 283-288, 1905. 



|| Ibid., pp. 285-286. 



