﻿Manchester Memoirs, Vol. xlix. (1905), No. 4. 7 



adapted to the measurements of such small values of rj as 

 occur at this stage of the solidification process.* 



Observations made within an hour of filling the tube 

 showed that the jelly behaved like a very viscous fluid, 

 the whole mass flowing through the tube when subjected 

 to pressure. To prevent the plug from slipping as a 

 whole, the walls of the tube were roughened by etching a 

 number of shallow rings by means of hydrofluoric acid on 

 the inside surface. After two hours, the jelly shows very 

 little viscosity, but possesses hysteresis to a great extent ; 

 that is, after removing the pressure causing a constant 

 deformation, the plug did not return to its original 

 position, but showed a permanent strain. This hysteresis 

 effect became less marked as the solidification went on, 

 until at about 20 hours after preparation it suddenly 

 disappeared, and the further alteration in the rigidity was 

 very slow, often being quite inappreciable in the remaining 

 observations extending over several days. This behaviour 

 seems to confirm the theory that solidification of matter 

 begins round a number of nuclei. In the state repre- 

 sented by the ascending branch we should then have a 

 number of globules of jelly in a more advanced stage of 

 solidification than the material surrounding them. On 

 subjection to pressure the more condensed masses would 

 be elastically deformed, and would at the same time slide 

 over one another, shearing the material between them, 

 which would unite again when the steady state of 

 deformation was attained. On removing the pressure the 

 elastically deformed portions would return slightly 

 towards their initial position, but the mass as a whole 

 would have a permanent strain. The behaviour of the 

 weaker portions under stress is illustrated by the fact that 



* Measurements with very stiff jellies have been made by Maurer, WiecU 

 Ann. 28, 1886, p. 628, Fraas, Wied. Ann. 53, 1894, P- I °74- 



