300 PHYSICAL PROPERTIES 



silica, be examined under high magnification they can all be 

 demonstrated, Hardy states (33) (34), to possess a fine open 

 spongy structure. When, for example, a 13 per cent solution 

 of egg-white is fixed with sublimate, sections are found to show 

 a sponge or net structure. Staining the section with iron- 

 hsematoxylin, with saturated solutions of acid and basic dyes or 

 even by evaporation to dryness in solutions of such dyes, failed 

 to produce the staining of any substance within the meshes of 

 the net, while pressure applied to the gel resulted in the squeezing 

 of fluid out of these interstices. The structure of the gel is 

 therefore that of an open sponge-work of solid, containing fluid 

 within its meshes. Direct experimentation with agar showed 

 that in a gel containing 1 per cent agar the solid framework is 

 a solution of water in agar, while the fluid contained in the inter- 

 stices is a dilute solution of agar in water; upon the heating the 

 system the two components become miscible in each other and 

 we obtain a homogeneous solution. Upon the basis of these 

 facts Hardy draws a far-reaching analogy between this system 

 (and other jellies which are heat-reversible) and the system 

 phenol-water, which, if it contains more than 71 per cent or less 

 than 76 per cent of phenol separates, at temperatures below 

 80 degrees, into two phases, the one a solution of phenol in water, 

 the other a solution of water in phenol. According to the view 

 developed by Hardy, the two cases differ only in the fact that 

 upon separation of the two phases in the agar-water system the 

 system retains a structure, while in the phenol-water system no 

 structure is retained. Essentially, he believes, the difference 

 between the two systems consists in this, that when the phenol- 

 water system separates into two phases the phases become sepa- 

 rated by the minimum possible surface, namely a plane; while 

 when the agar-water system separates into two phases they 

 remain in contact over an area far larger than the minimum. In 

 the latter case it would appear that the surface tension at the 

 surface of separation of the two phases is very low, so that the 

 force leading to a diminution of surface is indefinitely small. 



Pauli and Rona (72) object to the use which Hardy has made 

 of the term "phase" in. this connection. They point out that 

 the fluid which may be pressed out of an agar jelly may contain 

 from to 0.14 per cent of agar according to the magnitude and 

 mode of application of the pressure, and they urge, in considera- 



