21i8 EIGHTH PACIFIC SCIENCE CONGRESS 



CaClg during alkali-treatment favors jelly-strength. Taking advantage 

 of this, attempts have recently been made to manufacture agar-agar from 

 cheaper material, e.g., Gracilaria confervoides. 



Ill, Rheological Studies of Agar-hydrosol and Gel 



a) Visco-elasticity of agar-hydrogel (16):— The experimental pro- 

 cedure adopted was that used by Schwedoff (1889), Hatschek and Jane 

 (1926), and Poole (1926), the apparatus being composed of two concen- 

 tric cylinders, the intervening gap being filled with gel and the inner 

 cylinder being suspended by a tortion wire. When the top of the tor- 

 tion wire is twisted, the rigidity G of the gel is determined; the elastic 

 equilibrium is attained immediately, and the viscous flow commences, 

 so that the inner cylinder is observed to move gradually. 



Experimental results obtained are as follows. Elastic deformation 

 is Hookeian in the range of strain studied (shear rate 0.1-0.6), and ri- 

 gidity G markedly increases with the increase of concentration: 

 G(dyne/cm.2) 2.1xl0-i 4.3xl0-i 1.27 1.46x10 3.7x102 



Cone. (%) 0.039 0.053 0.062 0.12 0.28 



Viscous flow is anomalous; it increases along with the increase of 

 shear strain, namely with the increase of deflection of the inner cylinder. 

 The visco-elastic behaviour of agar-gel is described by the three-element 

 mechanical model. 



b) Thermo-elastic property of agar-hydrosol (n):— Aqueous solu- 

 tion of agar, gelatin, pectin, etc. or benzene solution of some metallic 

 soaps make elastic jellies. The principal characteristic of these gel states 

 is shape-durability and high elasticity in spite of a relatively high con- 

 tent of solvent. 



The thermo-elastic property of agar-hydrogel was studied according 

 to Meyer and Ferri's scheme (1935) for determining the elasticity of 

 rubber. Thus, both the energy contribution and the entropy contri- 

 bution to elasticity can be discussed from the stress-temperature curve 

 under a constant strain. 



The experimental device was the same as has been mentioned in the 

 previous section (a). Experimental results show that the elastic force 

 gradually decreases with increase of temperature. This means that the 

 elastic force of gel is concerned with the increase of internal energy and 

 also with that of entropy by deformation; this situation is similar to 

 the behaviour of metals and crystals. 



The nature of the high elasticity of gel seems to be somewhat dif- 

 ferent from that of rubber elasticity, which is chiefly attributed to the 



