402 COMPOUND PRODUCTS. CHAP. I. 



Varieties. Extract, or the extractive principle, is found in 

 a greater or less proportion in almost all plants 

 whatever, and is very generally an ingredient of 

 the sap and bark, particularly in barks of an as- 

 tringent taste. But still it is not exactly the same 

 in all individual plants, even when separated as 

 much as possible from extraneous substances. It 

 may therefore be regarded as constituting several 

 different species, of which the following are the 

 most remarkable. 



Extract of Catechu. This extract is obtained 

 from an infusion of the wood or powder of catechu 

 in cold water. Its colour is a pale brown ; and its 

 taste slightly astringent. It is precipitated from its 

 solution by nitrate of lead, and yields by distilla- 

 tion carbonic and carburetted hydrogene gas, leav- 

 ing a porous charcoal. 



Extract of Senna. This extract is obtained 

 from an infusion of the dried leaves of Cassia 

 Senna in alcohol. The colour of the infusion is 

 brownish, the taste slightly bitter, and the smell 

 aromatic. It is precipitated from its solution by 

 the muriatic and oxymuriatic acids, and when 

 thrown on burning coals consumes with a thick 

 smoke and aromatic odour, leaving behind a spongy 

 charcoal. 



Extract of Quinquina. This extract was ob- 

 tained by Fourcroy, by evaporating a decoction of 

 the bark of the Quinquina of St. Domingo in 

 water, and again dissolving it in alcohol, which 



