238 Mr. W. R. Dunstan and Miss L. E„ Boole. 



to some other constituent which is present as an impurity in this 

 acid, and cannot be separated from it. In this paper Buchheim does 

 not decide in favour of either of these hypotheses, but on the whole 

 leans towards the last supposition. A year later, the subject was 

 investigated by Schlippe,* who was apparently not familiar with 

 Buchbeim's observations. Schlippe showed that the vesicating con- 

 stituent, obtained by solution of the croton oil in strong alcohol, was 

 destroyed by heating it with alkalis. He concluded that it is not an 

 acid, but a polyhydric alcohol of the formula CigHuO* ; and he 

 proposed for it the name of crotonol. In 1873 Buchbeimf published 

 an account of further work on the vesicating constituent. Repeat- 

 ing the experiments of Schlippe, he came to the conclusion that this 

 observer was mistaken in considering crotonol as the active consti- 

 tuent of the oil. Buchheim maintains that his new experiments 

 have conclusively proved that the vesicating principle is an acid, 

 crotonoleic acid. This substance he isolated in the following manner: 

 croton oil was shaken several times with alcoholic ammonia, the 

 upper alcoholic layer, which contains the vesicating constituent, 

 being each time removed from the insoluble oil below. The alcoholic 

 solution was mixed with an aqueous solution of barium chloride, and 

 warmed. The barium salt thus formed was filtered off, washed and 

 dried. It was then repeatedly extracted with ether, which dissolves 

 the barium salt of oleic and crotonoleic acids, but leaves the barium 

 salts of other fatty acids (stearic, palmitic, &c.) undissolved. The 

 ethereal solution of the barium salts is decomposed by shaking it 

 with dilute hydrochloric acid. The ether, having been washed with 

 water, is distilled and the oleic and crotonoleic acids are then left in 

 the form of an oil. This oil is dissolved in alcoholic ammonia, and 

 the liquid fractionally precipitated with a solution of barium chlo- 

 ride, the last precipitate being subjected to a repetition of the 

 process until finally a barium salt having a constant composition is 

 obtained. By this means the less soluble barium oleate may be sepa- 

 rated from the more soluble barium crotonoleate. The acid regene- 

 rated from the barium salt is an oil, which Buchheim considered to 

 be the same as Schlippe's crotonol. 



Crotonoleic acid is slowly decomposed when heated with alkalis or 

 strong acids, losing its vesicating property. Buchheim did not pre- 

 pare the acid pure enough to admit of ultimate analysis, but from 

 its behaviour he concludes that crotonoleic acid is closely related to 

 the ricinoleic acid of castor oil. Its glyceride does not vesicate ; 

 and, according to Buchheim, croton oil contains the glyceride as well 

 as the free acid, so that, if the bland oil remaining after the removal 



* ' Annalen der Chemie und Pharmacie,' 1858, vol. 105, p. 1. 

 f ' Archiv der Heilkunde,' 1873, vol. 14, p. 4. 



