1895.] Nature of the Vesicating Constituent of Croton Oil. . 239 



numerous chemists and pharmacologists during the past forty years. 

 According to the researches of Buchheim, and more recently of Robert 

 and Hirscheydt, the vesicating action is due to an acid closely allied 

 to oleic acid, which has been given the name of crotonoleic acid. 

 This substance is now prepared on a large scale in Germany for 

 medical use, being extracted from croton oil by the method devised 

 by Kobert and Hirscheydt. This consists in saponifying with 

 barium hydroxide that part of croton oil which readily dissolves in 

 strong alcohol. The resulting barium salts are washed with water, 

 then dried, and repeatedly extracted with ether, which dissolves the 

 barium salts of oleic and crotonoleic acids. These salts are separated 

 by means of ether, which dissolves only the barium crotonoleate, and 

 this, when decomposed with dilute sulphuric acid and extracted with 

 ether, furnishes- the crotonoleic acid as a viscid oil. 



Since very little is known about this acid, even its composition 

 being undetermined, the authors prepared it with the object of 

 studying its properties and, if possible, of determining the constitu- 

 tion, since no fatty acid of known constitution exhibits the property 

 of vesicating. Starting with the crotonoleic acid prepared as 

 described above, the lead salt was obtained and submitted to a pro- 

 cess of fractional precipitation by adding successive quantities of 

 water to its solution in alcohol. By this means crotonoleic acid was 

 proved to be a mixture composed for the most part of inactive oily 

 acids, the lead salts of which are precipitated first, whilst the true 

 vesicating constituent (or its lead salt) is principally contained in 

 the last fractions, and represents but a small proportion of the 

 original material. It was observed that the conversion of the 

 crotonoleic acid into a lead salt did appreciably affect its vesicating 

 power. 



The supposed active constituent of croton oil, crotonoleic acid, 

 Laving thus been shown to be a mixture, the authors proceeded to 

 attempt to isolate the vesicating constituent from croton oil direct. 



By saponifying that parb of croton oil which is soluble in strong 

 alcohol with a mixture of lead oxide and water, and repeatedly frac- 

 tionating an alcoholic solution of the lead salts with water, the later 

 fractions, which possessed the greatest vesicating power, ultimately 

 furnished, when submitted to a series of fractionations, a resinous 

 substance having extraordinary power as a vesicant. This substance 

 could not be further resolved by repeating the process of fractional 

 precipitation of the alcoholic solution with water. The same sub- 

 stance was isolated from the so-called " crotonoleic acid," and the 

 authors propose to name it " croton-resin." To its presence the 

 vesicating property of croton oil is due. The composition of croton- 

 resin is expressed by the empirical formula C 13 H lb Oi. So far all 

 attempts to crystallise it, or to obtain crystalline derivatives from it, 



TOL. LV1I1. S 



