RECENT ADVANCES IN SCIENCE 403 



equilibrium relations. The theory that each particle which it 

 deposited on the crystal is in the same state of strain as the 

 crystal in its immediate neighbourhood is confirmed, so that 

 the relations between crystal and liquid are always reversible. 



Rawdon (Met. and Chem. Eng. 15, pp. 406-8, 191 6) makes 

 some interesting observations on the twinning of crystals of 

 electrolytically deposited copper. The tendency to twinning 

 increases with the current density and the effect of annealing 

 indicates that the electrolytically deposited crystals form under 

 conditions of stress. 



Schubnikov (Zeit. Kryst. Min. 54, pp. 261-66, 267-72, 1914, 

 from Jour. Chem. Soc. 112, ii. p. 449, p. 450, 191 7) in the 

 first paper deals with the influence of temperature variations 

 on the growth of crystals, and explains the growth of some faces 

 at the expense of others in this way, in preference to the theory 

 of varying solubility of the different crystallographic forms. In 

 the second paper he has investigated the relation between 

 supersaturation and external symmetry, and finds that the 

 latter tends to increase with the degree of supersaturation. 



The formation of striae and vicinal forms is discussed mathe- 

 matically by Grinakovskii (Jour. Russ. Phys. Chem. Soc. 48, 

 PP- 974-85, 1916, from Chem. Abs. 11, p. 1070, 191 7), who con- 

 cludes that it is due to the disturbance of the equilibrium con- 

 ditions, particularly of the thermal equilibrium of the contact 

 layer of liquid and crystal. 



Polymorphism. — In a number of papers Bridgman has made 

 an elaborate study of polymorphic changes. In the case of 

 the nitrates of the monovalent metals (Proc. Amer. Acad. 51, 

 pp. 581-625, 19 1 6) it is found that the rubidium, caesium 

 and thallium salts are similar, but the behaviour of silver 

 nitrate is very different. The ammonium and potassium 

 nitrates are both very complicated, and one new type of the 

 former and two of the latter, stable only under high pressure, 

 have been obtained. From a consideration of the phase 

 diagrams, especially at high pressures, it is concluded that the 

 alkali nitrates have complete similarity of structure. In a 

 second paper (ibid. 52, pp. 57-8, 1916) the velocity of poly- 

 morphic transformation for many substances has been measured 

 by determining the isothermal time rate of change of pressure 

 during the transformation. The velocity is not the same for 

 the two directions in a reversible transformation, while there 



