274 EXPERIMENTS ON ASTRINGENT VEGETABLES. 



ounces of water, at 52°, are required to 100 grains of extract 

 Therefiduum feldom amounts to ^ of the original weight of 

 the catechu ; and, in mod cafes, it is found to confift chiefly of 

 calcareous and aluminous earths, and*offine fand, which, by 

 accident or defign, had probably been mixed with the primi- 

 tive infufion at the time of its evaporation. 

 Alcohol diflolves A considerable portion of both kinds of catechu is foluble in 



much ; and alcohol ; but, after the action of alcohol upon it, a fubftance 

 leaves mucilage. _ , . , * , . , . 



remains of a gelatinous appearance and a light brown colour, 



which is foluble in water, and is analogous in its properties to 



gum or mucilage. 

 The peculiar ex- The peculiar extractive matter in the catechu, is much lefs 

 traft of catechu f ] u t>Ie in water than the tanning principle ; and, when a fmall 



is much efs fo- . *» • r 



luble than tannin quantity of water is u led to a large quantity ot catechu, the 

 in water. « quantity of tannin taken up, as appears from the nature of the 



ftrongeft infufion, is very much greater than that of the ex- 

 tractive matter. 

 And is more fo- The extractive matter is much more foluble in warm water 

 y than in cold water j and when faturated folutions of catechu 



are made in boiling water, a confiderable quantity of extrac- 

 tive matter, in its pure ftate, falls down, as the liquor becomes 

 cool. 

 Repeated lixivi- The peculiar extractive matter of the catechu may be like- 

 in 1 water, leave w ^ e obtained, by repeatedly lixiviating the catechu, when in 

 the peculiar ex- fine powder, till the fluids obtained ceafe to precipitate gela- 

 tract. t j ne . t j ie re f 1( j ua | foiid Wl \\ then De f ounf i to be the fubftance 



in queftion. 

 Its fenfible The pure extractive matter, whether procured from the 



qua lties. Bombay or Bengal catechu, is pale, with a faint tinge of red- 



brown. It has no perceptible fmell ; its tafte is flightly aflrin- 

 gent ; but it leaves in the mouth, for fome time, a fenfation of 

 fweetnefs, ftronger that given by the catechu itfelf. 

 Solution in water j ts f„i u ti n in water is at firft yellow-brown; but it gains a 

 tint of red by expofure to the air. Its folution in alcohol does 

 not materially change colour in the atmofphere ; and it is of an 

 uniform dull brown. 

 Habitude with The extractive matter, whether folid or in folution, was not 

 tefts > found to produce any change of colour upon vegetable blues. 



— with alkalis. It became of a brighter colour by the action of the alkalis ; 

 but it was not precipitated from its folution in water by thefe 

 bodies, nor by the alkaline earths. 



4. The 



