Nature of tlie Vesicating Constituent of Croton Oil. 239 



of the crotonoleic acid is saponified, the vesicating property is found 

 in the acids regenerated from the soap. 



In 1883 H. Senier,* apparently unaware of previous researches on 

 the subject, including those of Buchheim, published an account of 

 observations which led him to conclusions similar in some respects 

 to those previously arrived at by Buchheim. Senior found that 

 strong alcohol separates croton oil into two parts : a small part 

 which dissolves, carrying with it the whole of the vesicating consti- 

 tuent, and the main part which does not dissolve, but retains the 

 purgative power, although it has lost the vesicating property. The 

 vesicating constituent is not a free acid since it is not removed from 

 croton oil by agitation with aqueous sodium carbonate. When the 

 soluble oil is saponified with potash the vesicating property is no 

 longer exhibited by the soap ; but the acid regenerated from the soap 

 vesicates powerfully. By a process of fractional saponification, 

 followed by ft actional precipitation of the fatty acids, Senier con- 

 cluded that the vesicating constituent is a non-volalile fatty acid, 

 closely resembling oleic acid. The glyceride of this acid is less 

 readily saponifiable than the other glycerides present in croton oil ; 

 and, similarly, the acid is regenerated first when the soaps are 

 decomposed, being thrown out with the acids of lowest melting- 

 point. 



In 1890, the question as to the nature of the vesicating constituent 

 was reinvestigated by Hirscheydt,'|' working in Professor Robert's 

 laboratory at Dorpat. It is pointed out, in his voluminous paper, 

 that alcohol fails to effect a sharp separation of the vesicating from 

 the non- vesicating portion of croton oil ; that different specimens 

 vary in their solubility in alcohol ; and that, although the vesicating 

 constituent is far more soluble, yet, if sufficient alcohol be used, the 

 whole of the oil will gradually pass into solution. A repetition of 

 Buchheim's experiments confirmed his conclusion that a non- volatile 

 fatty acid is the cause of the vesicating property ; and for this acid it 

 was proposed to retain the name of " crotonoleic acid," originally 

 suggested by Buchheim. By purifying the barium salt, the acid was 

 ultimately obtained in a purer condition than it had been produced 

 by Buchheim. It was not submitted to ultimate analysis; but since 

 its barium salt, prepared in the pure state by fractionally precipi- 

 tating the sodinm salt with barium chloride, contained less barium 

 than barium oleate, it is judged to have a higher molecular weight 

 than oleic acid. The acid is a brown oil at the ordinary temperature, 

 and is very unstable, especially when in contact with alkalis, which, 

 if heated with it, slowly destroy its vesicating power. 



The following improved process for the isolation of crotonoleic acid 



* ' Pharm. Journ.,' Ill, vol. 13, p. 446. 

 f ' Dorpat Arbeiten,' 1890, vol. 4, p. 5. 



