38$ Confederations on Vegetable Extra&s. 



diftinguiflied in plants which, like the tithymalli, give milky 

 juices: nature prefents us with fuch a combination in refinous 

 gums, fuch as gum ammonia, afTa-faetida, &c. 



6th, Extractive matter: it is always united with other 

 immediale materials of vegetables, and is found in greater 

 quantity in plants which have come to maturity, in ligneous 

 roots, wood, bark, and dried leaves, than in vegetables or 

 thofe parts of vegetables where mucous matter prevails. 



7th, Colouring principle : tberc are two kinds of it. 



ift, That which, combined with mucous or extractive 

 matter, is folubie in water; it is feen in flowers under the 

 ikins of fruit, in Indian wood, the root of madder, &c. 



2d, That which, when fixed on any refmous fubftance 

 united with extractive matter, is rather carried away than 

 diflblved by boiling water, and may form part of extracts. 

 It e\iiis in the root of the walnut-tree, in fandal wood, in 

 the bark of the alder-tree, in the hnfk of walnuts, &c. 



8th, The tanning principle. This fubftance has an aftringent 

 favour, which particularly diftinguifhes the oak, the gall nut, 

 Sec. The maceration of thefe fubftances has the property of 

 precipitating and rendering infoluble the animal gelatin, of 

 hardening it in leather, which by thefe means can be pre- 

 ferved for a long time without alteration. 



The tanning principle is often accompanied with gallic 

 acid, which may be diftinguifhed by the property it has of 

 precipitating iron black, and which was thought to belong 

 to that principle called aftringent, and which bears the name 

 of tannin. 



9th, The aroma. This is the volatile and odorous prin- 

 ciple, which, being differently modified in many plants, gives 

 to each of them an odour by which it is characterized. 



It refides, in particular, in volatile oils. Perhaps it is no- 

 thing elfe than thefe oils themfelves, more or lefs combined 

 wiih other vegetable principles, which facilitate its folution 

 in water, and which, in feveral cafes, give it a certain fixity : 

 but fome chemifts have entertained doubts reflecting the ex- 

 igence of aroma diftinct from the other materials of vege- 

 tables. 



f^xtract of opium, indeed, retains the virous odour of the 

 poppy, uotwithftanding the continued heat which the juice of 

 that plant experiences during its evaporation. 



Extracts of rue, favine, and wormwood, retain the odour 

 of thefe plants ; and the fugar, carried to a very high tempe- 

 rature in the preparation of rofe and orange flower tablets, 

 flill exhales a very feniibie odour of the flowers which have 

 been employed. 



And 



