﻿M andies ter Memoirs, Vol. xlix. (1905), No. 4. 



IV. On the Rigidity of Gelatine. 



By H. MORRIS-AIREY, M.Sc. 



Received and read January 24th, 1905. 



The material used in the following experiments is a 

 jelly made by dissolving gelatine* in warm water. On 

 cooling, the mass becomes an elastic solid which has some 

 interesting properties. 



For all ordinary pressures (i.e., up to 5 or 6 atmos- 

 pheres) the material shows no diminution in volume but 

 it is very easily distorted by tangential stress. This latter 

 property has been made use of in optics by Clerk- 

 Maxwell to exhibit the action of crystalline media on 

 polarised light. 



If such a jelly is saturated with a salt solution many 

 of its physical properties, such as velocity of electrolytic 

 ions in it, are approximately the same as those of the 

 aqueous solution of the salt. Consequently jellies of this 

 kind have found application in experiments where con- 

 vection currents within the salt solution were to be avoided. 



An interesting property is mentioned by Mactear.f 

 A crystal embedded in a salt solution jelly, continues to 

 grow as a single crystal developing into a very symmetrical 

 specimen, while in an ordinary aqueous solution this is 

 hindered by the formation of other lesser crystals. He 

 attributes the formation of the very perfect selenite 

 crystals found in plastic clay to this cause. 



It was in connection with the use of jelly plugs in 

 diffusion experiments that the method of measuring the 

 rigidity of gelatine solutions was suggested. 



*That known commercially as "Nelson" leaf gelatine was used, 

 t Transactions of Inst. Mining and Metallurgy, XII., 1902, p. 132. 



February 16th, ipoj. 



