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XX. On the Velocity of Solidification and Viscosity of Super* 

 cooled Liquids. By Harold A. Wilson, B. A. {Camb.), 

 D.Sc. (Lond.), M.Sc. (Vict.), 1851 Exhibition Scholar, 

 Allen Scholar. Cambridge University*. 



IN the following paper an account is given of a series of 

 experiments, the object of which was to obtain infor- 

 mation on the influence of the viscosity of a supercooled 

 liquid on its rate of solidification. When solidification is 

 started in a supercooled liquid, rays of solid grow in the 

 liquid with a definite velocity the relation of which to the 

 initial supercooling has been determined f for a number of 

 substances, e. g. phosphorus and benzophenone. In consi- 

 dering the nature of the observed relation between the velocity 

 and the supercooling, it is important to take into account the 

 production of heat which accompanies the solidification, and 

 which must raise the temperature of the surface at which the 

 solidification takes place ; so that the observed relation may 

 differ greatly from the relation between the velocity and the 

 temperature of the solidifying surface. 



In a previous paper " On Velocity of Solidification " $ 1 

 have shown that the general character of the relation ob- 

 served between the velocity of solidification and the super- 

 cooling of the liquid can be explained in detail by supposing 

 the solidification to be due to the difference between the 

 internal pressures in the liquid and solid, and that the mole- 

 cules at the surface of separation between the solid and 

 liquid are urged from the liquid into the solid by this differ- 

 ence in the internal pressures. Using the method given 

 by Van't Hoff for calculating the osmotic pressure of a salt 

 in solution from the depression of the vapour-pressure, and 

 making certain assumptions described in detail in the paper 

 just referred to, the following formula for the velocity was 

 obtained: — 



F o -0 



where v is the velocity of solidification, F the latent heat of 

 fusion of one gram of the solid, A the force required to give 

 unit velocity to one gram of the liquid diffusing through 

 itself, a the thickness of the layer of molecules at the sur- 



* Communicated by the Author. 



t Gernez, Journ. de Phys. [2] ii. p. 159. Friedlauder & G. Tammann, 

 Zeitschr. f. Phys. Chem. xxiii. p. 326, arid xxiv. p. 152. 

 X Proc. Camb. Phil. Soc. vol. x. pt. 1. 



