might have contained seme of the poisonous principle as 

 an impurity, but that it would not produce the dermatitis 

 if prepared in a pure state. He therefore prepared a 

 quantity of the acid hy distilling the finely divided fresh 

 plant with steam. The yield was increased by acidulating 

 the mixture with sulphuric acid before the distillation. 

 The acid distillate so obtained was freed from a non-poison- 

 ous oily substance by shaking the solution with ether. 

 Barium and sodium salts were made by neutralizing the acid, 

 and were purified by crystallization. Analysis showed them 

 to be salts of acetic acid, and they gave the characteristic 

 tests for this acid. The toxicodendric acid of Maisch was 

 thus shown to be acetic acid, and was therefore not the poison- 

 ous principle of the plant. 



Pfaff obtained the active principle by the following 

 process: The plant was extracted with alcohol, the alcohol 

 was distilled off, and the residue was taken up in ether. 

 The ether solution was washed with water and dilute sodium 

 carbonate solution, an.d the ether was evaporated. An oily, 

 black, poisonous substance partly soluble In alcohol was 

 obtained. To get the active principle in a pure state, 

 this residue was extracted with alcohol and filtered and 

 the filtrate was precipitated fractionally by lead acetate. 

 The final precipitates consisted of the lead compound of 

 the poison in a pure state. On decomposing the lead com- 

 -16- 



