[Pkoc. Eoy. Soc. Victoria, 30 (N.S.), Pt. II., 1918]. 



Art. XV. — A Covtrihution to the Theory of Gel Structure. 



By W. a. OSBORNE, M.B., D.Sc. 



(From the Physiological Laboratory, University of Melbourne). 

 [Read 13th December, 1917]. 



It is now generally admitted that a gel is a diphasic system, but 

 divergent views are held concerning the nature and possible vec- 

 torial characteristic of the more solid phase, and the forces which 

 hold the more liquid phase in position. Whether the meshwork of 

 the more solid phase is composed of micro-crystals, or is truly 

 amorphous, or whether both can give rise to gel structure, further 

 refinements in ultra-microscopy may determine. But Avhatever 

 view may be correct, the question is unaffected, whether the " fila- 

 ments," " needles," or micellae assume a definite arrangement 

 under the influence of forces akin to those that produce crystallisa- 

 tion. Is the meshwork of the more solid phase devoid of any vec- 

 torial characteristic, or is such actually present? 



To throw some light on this problem I commenced certain experi- 

 ments in 1909 on the shapes of bubbles found in strong gelatine 

 gels when decompressed after being subjected, when warm and dur- 

 ing setting, to gas under pressure — generally COr,. The ordinary 

 fracture of a gel can be described as " perfectly conchoidal," and 

 this in itself indicates that like obsidian or ordinary flint homo- 

 geneity of structure may be present. But such reasoning cannot 

 be pushed very far, for conchoidal fracture can be given by crystal- 

 line substances, notably quartz. It was this consideration that led 

 me to exaimine the internal fractures produced by bubble forma- 

 tion. The simplest way to carry out the experiment is to subject 

 warm 10% gelatine solution in a sparklet syphon to the action of 

 CO2 under pressure. I have also employed the Leonard Hill high 

 pressure chamber with gas pressures of 10-20 atmospheres but the 

 small quantity of gelatine that can be used is here a disadvantage. 

 On decompression the appearance of the jelly is remarkable. Each 

 bubble that forms is lenticular, or apparently a disk of great thin- 

 ness, and entirely in one plane. I communicated this result to the 

 late Mr. William Sutherland, and he wrote me as follows, under 

 date May 7th, 1910;— 



" The form of the gas cavity will depend on the rigidity of the 

 jelly in the following way : The spherical form characteristic of 



