* 



20 



will the membrane be quite impermeable to soap, and further, since 

 dilute solutions in particular are appreciabl}^ hydrolysed, hydrolysis 

 will be developed by the continued removal of the alkaline products 

 of hydrolysis, leaving behind the insoluble or coUoidal acid soap, 

 the whole forming an instance of membrane hydrolysis. In the 

 second place, however, one practical consideration vitiates the niceties 

 of theoretical interpretation, that is that quite exceptional opportunities 

 are afforded for decomposition of the soap by the carbonic acid from 

 the air or from the large quantities of water emj)loyed. For instance, 

 as we have seen Moore and Pai'keri^ obtained an osmotic pressure 

 50 times too small, and were unable to detect any alkali coming 

 through ordinary parchment. Various other investigators, Rotondi, 

 Botazzi, and VictorofE-' found that acid soaps or possibly even free 

 fatty acid remained behind on dialysis under such conditions. How- 

 ever, they, like Mayer, Schaeifer, and Terroine-'* found that as long as 

 the solution was kept alkaline some of the soap did pass through the 

 membrane. 



VI. — Solidification and Gelatinisation of Soap Solutions. 



The solidification and gelatinisation and salting out of soap solutions 

 afford penomena of extraordinary interest which have not received 

 adequate interpretation in the literature. 



Upon cooling, or upon the addition of various substances white 

 opaque curd may be formed, or again, there may be obtained typical 

 gels, clear and transparent or ranging through various degrees of 

 cloudiness. These two very distinct forms, white curd and clear 

 gel have always hitherto been confused with each other and referred 

 to indiscriminately. Hence there has been controversy as to whether 

 they were colloidal at all. 



Sodium oleate solutions as studied by Miss Laing present a 

 particularly mteresting case since here it is possible to obtain one and 

 the same solution at any one temperature in the form of transparent 

 sol, clear jeUy, or white opaque curd. The conductivity of a given 

 soap solution is independent of whether it is studied as sol or clear 

 gel. Again the concentration of sodium ions present is also indentical 

 in the two cases. 



We are tending towards the opinion that in a gel there exist well- 

 developed strings of long molecules forming an exceedingly fine 

 filamentous structure which accounts for the elasticity of gels and 

 also for the fact that they exhibit more or less clearly oriented 

 properties, such, for instance, as the lenticular, fauiy definitely 

 oriented, form of bubbles generated wthin gels. This assumed 

 structure is, however, not resolvable under the ultramicroscope, as 

 is only to be expected. If we are able to obtain sufficiently definite 

 evidence for this, it would appear that the same forces are in play 

 here as account for the phenomena of crystalline liquids and liquid 

 crystals. There is a great deal of circumstantial evidence for this. 

 It would serve also to explam the incipient structure which most sols 

 develop on standmg and which is such as prevents for example, 

 definite measurements of viscosity from being taken independent 



