244 Dr. H. A. Wilson on the Velocity of Solidification 



cooling usually shows a very small rate of increase of velocity 

 when the supercooling is small. This is shown in fig. 1, where 

 the velocity- curve produced cuts the axis of temperature at 

 37°, whilst the melting-point of the salol was about 41 o, 0. 

 Still some indications of partial melting occurred at about 37°; 

 and it is very probable that if the substance were cpaite pure, 

 then the very small rate of increase of tho velocity near the 

 melting-point would not occur. Tammann (loc eit.) has shown 

 that purifying a substance always diminishes this region of 

 small velocity; and consequently, for the purpose of testing 



the formula v — Gy-, I have measured the supercooling from 



the point (37°'0) at which the velocity-curve shown in fig. 1 

 cuts the temperature-axis. 



To get the value of C in the formula v—C^ the values of 

 the velocity (v) and viscosity (V) were taken at 22°, at which 

 temperature s is 15°; hence C= ^ =5*74. 



The following table shows the results obtained, using the 

 formula v = 5*74^ and values of V taken from the curve for 

 the viscosity of salol. 



1 





1 



1 



1 v 



1 

 v. 



j Temp, 



.s. 



V. 



=5-74 *, 



(Found.) 



o 



o 









35 



2 



10-0 



115 



1-25 



33 



4 



107 



2-14 



2-5 



31 



6 



120 



2-90 



3-2 



29 



8 



135 



3-40 



3-7 



27 



10 



150 



3-82 



39 



25 



12 



170 



405 



4-0 



21 



16 



225 



4-08 



41 



19 



18 



25-0 



4-13 



41 



15 



22 



31-6 



4-00 



4-1 



The agreement between the found and calculated values of 

 v is sufficiently good. The independence of the velocity and 

 the temperature from 15° to 25° thus appears to be due in 

 this case to the viscosity being approximately proportional to 

 the supercooling between these limits of temperature. 



The formula v = C^ thus represents the variation of the 



