240 Mr. W. R. Dunstan and Miss L. E. Boole. 



is suggested by Hirsebeydfc : — The part of the croton oil which is 

 readily soluble in strong alcohol is heated on the water bath with a 

 hot saturated solution of barium hydroxide, until saponification is 

 complete. The barium soap thus formed is well washed with water, 

 until the soluble barium salts (acetate, butyrate, tiglate, &c.) are 

 removed, and it is then dried by warming it in a vacuum. The dried 

 mass is next repeatedly extracted with ether, which dissolves the 

 barium salts of oleic and crotonoleic acids, but not those of palmitic, 

 stearic and other solid fatty acids. 



In order to separate the barium crotonoleate from the barium 

 oleate which accompanies it in the residue left on the evaporation of 

 ethereal solution, the mixture is extracted with cold absolute alcohol, 

 which dissolves only the crotonoleate. The barium crotonoleaie thus 

 obtained is decomposed by the addition of dilute sulphuric acid, and 

 the crotonoleic acid separated by extracting the mixture with ether 

 in the usual manner. 



By this means Hirscheydt claims to have produced crotonoleic acid 

 in a purer and more active condition than that in which it was ob- 

 tained by Buchheim. He points out, however, that the new process 

 is not a wholly satisfactory one for the production of the acid, since 

 some is inevitably decomposed by the barium hydroxide, even if every 

 precaution is taken to avoid over- heating the mixture during saponi- 

 fication. 



Crotonoleic acid thus prepared has been employed medicinally, 

 and is now an article of commerce. 



It will be seen from the foregoing brief sketch of previous experi- 

 ments on the nature of the vesicating constituent of croton oil that, 

 although conflicting accounts have been given, the evidence which 

 has been so far accumulated goes to prove that the active substance 

 is the glyceride of an acid to which the name of crotonoleic acid is 

 given, the acid, as well as its salts, having vesicating properties. It 

 is, however, very doubtful, from the nature of the processes which 

 have been employed to isolate the compound, and from the descrip- 

 tion of its properties, whether it is a single substance. It appeared 

 to us important to attempt to obtain the pure compound and then to 

 ascertain precisely its chemical constitution, so that we might be able 

 to understand the kind of structure which is associated with the 

 vesicating property, especially since no other fatty acid of known 

 constitution exhibits this peculiarity. 



'Examination of Crotonoleic Acid. 



The crotonoleic acid used in these experiments was either prepared 

 by ourselves from croton oil, following the Dorpat directions given 

 above, or it was procured from Merck of Darmstadt, who prepares 



