SECT. VII. EXTRACT; 401 



might itself be regarded as the true extractive 

 principle. 



With this object in vieWj Vauquelin commenced 

 a series of experiments chiefly upon the sap and 

 expressed juices of plants, during the process of 

 which he remarked that they always began to ac- 

 quire a darker shade of colour from the moment 

 they were exposed to the air ; and that during their 

 evaporation a brown or reddish pellicle was formed 

 on the surface, which afterwards broke into flakes 

 and remained insoluble. Similar phenomena were 

 found to take place in pharmaceutical extracts, and 

 the longer the evaporation was continued, the more 

 of the insoluble flakes were formed. This was ac- 

 cordingly regarded as a detection of the true ex- 

 tractive principle, and the formation of the pellicle 

 and flakes was found to be the result of its absorp- 

 tion of a portion of the oxygene of the atmos- 

 phere, to which it was thus found to have a strong 

 affinity. 



Its distinguishing properties are the following. 

 It is soluble in water as it is obtained from the 

 vegetable, but becomes afterwards insoluble in con- 

 sequence of the absorption of oxygene from the at- 

 mosphere. It is soluble in alcohol ; and it unites 

 with alkalies, and forms compounds which are so- 

 luble in water. When distilled it yields an acid 

 fluid impregnated with ammonia, and seems to be 

 composed principally of hydrogene, oxygene, car- 

 bon, and a little nitrogene. 



VOL. i. 2 D 



