242 Mr. W. R. Dunstan and Miss L. E. Boole, 



the pure active substance. Starting with crotonoleic acid, and with, 

 the last fraction of the first operation, repeating several times the 

 process of fractional precipitation (assisting the subsidence by the 

 addition of kaolin), a substance was obtained the vesicating power of 

 which did not seem to be increased by further treatment. The 

 quantity produced from the crotonoleic acid was, however, compara- 

 tively small, and, as the process of obtaining the "acid" itself from 

 croton oil is extremely tedious and unproductive, we decided to seek 

 for some other method of isolating the active substance, it being no 

 longer of any importance to work with crotonoleic acid, since we had 

 conclusively proved this substance to be a mixture. 



Isolation of the Vesicating Constituent from Croton Oil. 



To begin with, an attempt was made to prepare a mixed lead salt 

 by precipitation from the sodium salts resulting from the saponifica- 

 tion of croton oil with soda. The croton oil dissolved in alcohol was 

 boiled for some hours with alcoholic soda. The soap thus prepared 

 was found to be non-vesicating, and so also were the fatty acids 

 regenerated from it. It was therefore certain that the vesicating 

 constituent of croton oil is decomposed by heating with alkalis, a 

 conclusion which has since been substantiated by numerous experi- 

 ments. 



For this reason the lead salts were prepared by direct saponifica- 

 tion of croton oil with a mixture of lead oxide and water. The lead 

 " soap " thus produced was a yellowish-white sticky mass, possessing 

 apparently all the vesicating power of the original oil. After having 

 been thoroughly washed with warm water, the soap was dried in the 

 water bath, mixed with sand, and the powdered mixture digested 

 with ether in a stoppered bottle for about four weeks. The ether 

 was then poured off, and the digestion repeated during one week 

 with two successive quantities of ether. The ethereal solutions were 

 mixed together and distilled, when a thick brown sticky mass 

 remained ; and this seemed to be considerably more vesicating than 

 the original lead soap; the residue of lead salt insoluble in ether 

 was much less active than the original mixture, whilst by repeated 

 extraction of a part of it with ether it became almost devoid of vesi- 

 cating property. It is thus clear that the vesicating substance passes 

 into solution in ether together with lead oleate. The ethereal 

 residue was now extracted several times with strong alcohol, and, 

 although only a small proportion dissolved on each occasion, the 

 material became less and less vesicating and finally quite inactive. 

 By this means the greater part of the lead oleate was separated, 

 whilst the whole of the vesicating substance was dissolved by the 

 alcohol. The alcoholic solution left on distillation a brown, nearly 



