Nature of the Vesicating Constituent of Croton Oil. 243 



solid substance, having extraordinary power as a vesicant. Alkalis, 

 even in the cold, slowly decomposed it, the vesicating property being 

 gradually lost. The acid recovered from this material, which was 

 presumably a lead salt, proved to be highly active. During this 

 regeneration we were surprised to notice that the material contained 

 very little lead, so little as to render it almost impossible for the 

 vesicating substance to be itself a salt of lead. In order to investi- 

 gate this important question, some of the material was dissolved in 

 alcohol and precipitated with a solution of sodium carbonate. The 

 lead carbonate, which was but little, having been filtered off and the 

 alcohol removed by boiling the liquid, the solution of sodium salts 

 was extracted with ether. This dissolved a small quantity of a 

 yellow oil, which nearly solidified on standing, forming a transparent 

 resinous substance. This was proved to be more active as a vesicant 

 than any substance hitherto prepared. It burned without ash and 

 was therefore not a sodium salt. The solution which had been 

 extracted with ether contained "soap," which was inactive, as were 

 also the fatty acids regenerated from it. Similarly, if an alcoholic 

 solution of the sodium salts (prepared from the lead salts) is precipi- 

 tated with silver nitrate, the silver salt is found to be inactive ; 

 but if the filtrate is extracted with ether a powerfully vesicating 

 resinous subslance is removed which contains no silver; and it was 

 thus ascertained that the vesicating constituent of croton oil is a 

 resinous substance which is not an acid and cannot be saponified by 

 a mixture of lead oxide and water. This substance may be pro- 

 visionally named " croton-resin." 



Isolation of Croton-resin from Crotonoleic Acid. 



It now became of interest to show that crotonoleic acid, the sup- 

 posed active constituent of croton oil, owes its activity to the croton 

 resin it contains, and not to the " acid " which is present. Some 

 quantity of crotonoleic acid was heated with a mixture of lead oxide 

 and water. The resulting lead soap was thoroughly washed with 

 water and extracted with alcohol, which dissolved about one-half. 

 The alcoholic solution was mixed with aqueous sodium carbonate, 

 the alcohol dissipated, and the aqueous solution extracted with ether 

 until it became virtually inactive. The ethereal solution left, on 

 evaporation, the croton resin which we had previously obtained 

 from croton oil. The inactive aqueous soap solution, when decom- 

 posed, furnished a mixture of fatty acids, which was quite inactive. 



By a different method of procedure the same result was obtained. 

 Crotonoleic acid was warmed with aqueous sodium carbonate, which 

 left a portion, chiefly croton resin, undissolved. As soon as action 

 was over, the liquid was extracted with ether, which removed the 



