368 Mr. S. B. Schryver and Miss M. Hewlett. Investigations 



manner without added salts, the diphasic erosion curves were not obtained, 

 and, generally, the solutions with low surface tensions had a greater erosive 

 action than those with higher tensions. When the sel contained an added 

 salt, however, a diphasic curve was always obtained, but the breadth of the 

 " zone of instability " and the amount of erosion within this zone varied 

 from salt to salt. In the second phase of the curve the solutions of 

 low surface tensions exerted the greatest erosive action. Of particular 

 interest is the action of sodium lactate on the gel containing potassium 

 chloride (X/ 8), which shows a very narrow '-'zone of stability," but a very 

 active erosion within this zone. The results are given in Table VI. 



Table VI. — Erosive Action of Sodium Lactate on Cholate Gels. 





Concentration of Lactate. 



N/20. 



2N/20. 



3N/20. 



4N/20. 



5N/20. 



6N/20. 



7N/20. 



8N/20. 



G-el without 



11 





40 



>75 



>75 



>75 



>75 



>75 



added salt 



















Gel containing 



17 





>75 



21 



33 



>75 



>75 



>75 



N/8 KC1 



















It will be noticed that the erosion is very large in the concentration 

 2X720— 3N/20, but small in that of 3X/20— 4X/20. 



The salt solutions in all these experiments were made by neutralising 

 exactly to phenolphthalein 2X solutions of sodium hydroxide with the acid, 

 and then diluting with water till the concentrations were normal. 



Theory of the Action of Salts on Gels. 



The results recorded indicate that the action of salts on a gel system is a 

 complex one, and that tbe stability is in all probability the resultant of 

 several different factors acting simultaneously. In the following pages an 

 attempt is made to summarise these. Certain of the generalisations will 

 refer more especially to the cholate gel, whereas others will apply to gel 

 structures in general. 



The phenomena accompanying the formation of the cholate gel have been 

 described in a former paper,* and these indicate that the gel itself consists of 

 two phases, viz., a eholate-poor phase (designated hereafter as the " acmeous 

 phase ") and a cholate-rich phase (designated as the " cholate phase "), which 

 during gel-formation gradually increases in bulk until its parts are more or 

 less coterminous throughout the system. When this gel is introduced into a 

 * ' Koy. Soc. Proc.,' B, vol. 87, p. 366 (1914). 



