GELATINIZATION AND COAGULATION 303 



in the extent of the surface which separates the phases, but also 

 in the variabiHty of the composition of its phases, in this respect 

 resembhng rather the system hydrated siUca-water, investigated 

 by van Bemmelen (1). 



An inversion of the external and internal phases of a diphasic 

 system, similar to that observed by Hardy on increasing the con- 

 centration of gelatin in the system gelatin-alcohol- water, may also 

 be observed in the system olive oil-alkahne water, on increasing 

 the proportion of oil to water (84) (85), and is here manifestly 

 due to the inability of a limited quantity of alkaline water to 

 surround and envelop an unlimited quantity of oil. 



The question has been raised whether the jelly which is formed 

 by gelatin dissolved in water (instead of alcohol-water mixtures) 

 really possesses a structure analogous to that observed by Hardy 

 in ternary systems. It has been urged that this structure is 

 an artefact arising out of partial coagulation of the protein, 

 since it is not directly visible in binary systems. The action of 

 coagulants upon jellies which already possess a structure of this 

 type, however, is not to otherwise alter but merely to coarsen 

 the structure. This is due to loss of water on the part of the 

 colloid-rich droplets with a consequent diminution of the volume 

 of the colloid-rich phase and an increase in the volume of the 

 more fluid interstices. This can be shown, not only by direct 

 observation, but also by the relative ease with which water can 

 be expressed from the jelly before and after "fixation." From 

 Poiseuilles' law for the outflow of liquids from capillary tubes, 

 it follows that the pressure required to express the fluid from the 

 interstices of a gel at a given rate must vary approximately as 

 the inverse fourth power of the diameter of the meshes, although, 

 of course, the variable viscosity of the expressed fluid will be a 

 factor introducing departures from this simple law. Now a 

 hydrogel containing 13 per cent of pure gelatin at a tempera- 

 ture of 15 degrees will endure a pressure of 400 pounds to the 

 square inch without expression of water; after fixation with 

 formalin or corrosive sublimate, however, the fluid can be ex- 

 pressed from the gel like water from a sponge, with simple hand- 

 pressure (33). 



Since more complete coagulation does not alter the type of 

 structure possessed by jellies of partially coagulated protein, 

 but merely coarsens it, it is a fair inference that jelhes which 



