Production of Soap Jellies. 



115 



of the aqueous phase of an emulsion of oil dispersed in water, and 

 that the emulsion subsequently broke down, the oil and water 

 layers separating. This effect was believed to be attributable to 

 the precipitation of the surface film of soap on which the stability 

 of the emulsion depended. To test this question Na oleate was 

 treated with salt at different concentrations, and it was found that 

 at .4 to 45M NaCl complete precipitation of the soap took place. 

 It was noted, however, that prior to precipitation a tendency to 

 jelly formation was exhibited in the zone from .2M NaCl to .4 or 

 .45M NaCl. 



An attempt to repeat this experiment with a soap, which had 

 been slightly acidified either by the addition of a minute quantity 

 of oleic acid or of mineral acid, gave an entirely different result, an 

 opalescence with increasing cloudiness and tendency to precipita- 

 tion was noted between .2M and .4M NaCl, followed by com- 

 plete precipitation at .45M NaCl. Further tests using varying 

 proportions of soap, varying proportions of NaOH, and of NaCl 

 and other salts of Na, brought out the remarkable fact that, as 

 long as the soap employed was not too greatly diluted and was 

 slightly alkaline, a jelly would be formed at all points between 

 .2M Na and .45M Na regardless of whether the Na was derived 

 from NaOH, from NaCl or other salts of Na. 



In very concentrated soap solutions or in very strong alkali 

 the jelly formation commences at a somewhat higher concentration 

 and continues also somewhat above 45M. But it may be stated 

 as a general principle that a zone of jelly formation obtains within 

 these ranges, provided the original concentration of OH ions is in 

 excess of the amount required to produce a strong pink coloration 

 of the soap solution with phenolphthalein. If insufficient alkali 

 is present as a result of the addition of small amounts of organic or 

 mineral acids to the system, precipitation instead of jelly formation 

 is observed. Since jelly formation commences and ends at a 

 given strength of the Na salt almost regardless of the nature of the 

 anions present provided there is a sufficient initial concentration 

 of OH ions, it seems probable that the explanation is as follows: 



A dispersion of Na oleate in water represents a dispersion of 

 particles of oleic acid by means of NaOH. Further additions of 

 NaOH lead to a more perfect dispersion of the soap particles, 



