and Viscosity of Supercooled Liquids. 245 



velocity with the temperature at which it takes place in a very- 

 satisfactory manner in the case of salol. 



In the case of substances having greater velocities of soli- 

 dification than salol, it is not easy to ' determine the rise in 

 temperature during solidification. I have made measure- 

 ments of the viscosity and velocity of solidification of super- 

 cooled salol, beuzophenone, benzoic anhydride, and azobenzol, 

 for which measurements of the velocity have also been made 

 by Friedlander and Tammann (loc. cit.), and my results for 

 the velocity do not differ much from those given by them. 

 Benzoic anhydride has a maximum velocity of about 35 jj^' ; 

 so that the thermocouple would only be in the boundary for 

 Ob* sec, which is probably not long enough to enable it to 

 take up the temperature at the boundary. 



Another difficulty was that the galvanometer available had 

 rather a long period of swing, so that it could not be used for 

 measuring so sudden a rise of temperature. An attempt was 

 made to increase the time during which the couple was in the 

 boundary, by moving it along with a velocity nearly equal to 

 the velocity of the boundary; and an apparatus was made 

 which automatically did this. Unfortunately, however, the 

 motion of the couple in the liquid nearly always caused it to 

 solidify, and the couple became fixed in the solid. I believe 

 that this could be prevented by taking care not to allow the 

 wires from the couple to carry any of the liquid into the cold 

 air above the bath, and by heating the couple with the liquid 

 for a long time ; but I am not able at present to devote any 

 more time to these experiments, and shall therefore simply 



use the results obtained to test the formula v = C^. without 



correcting for the rise in temperature during the solidi- 

 fication. 



The following Tables give the results obtained with 

 benzoic anhydride. The velocity was measured between two 

 marks 10 cms. apart on a tube 0'3 cm. in diameter. The 

 apparatus already described was used for the viscosity 

 determinations. 



Phil Mag. S. 5. Vol 50. No. 303. Aug. 1900. S 



