204 0N VARIOUS SPECIES OF CINCHONA. 



rated. Water itself redissolves this substance, though it has 

 been separated from it by evaporation ; but it requires a larger 

 quantity, than when it is accompanied with the other princi- 

 ples of cinchona, which seems to show, that these principles 

 promote the solution in water. 

 This not ran. If the infusions of. bark be allowed to cool several times, 

 t\ Te u f W j "n before tne y are evaporated to dryness, at each cooling they let 

 fall a matter similar to that just mentioned. It was formerly 

 supposed, that this substance was rendered insoluble by con- 

 biningwitb oxigen, but the effect appears rather to be owing 

 to the insufficiency of the water. 

 In this the bit- It is this sort of resinous matter, that gives to bark and its 

 ' emess resi | ■ * infusions their bitter taste : for if these sediments be separated 

 as they form, and the infusion thus boiled down be afterward 

 made up to its former quantity by the addition of water, it 

 will no longer possess the same degree of bitterness. The 

 ■uhole"of this matter however cannot thus be separated from 

 water; for the other principles of the cinchona always retain 

 a pretty large quantity in solution. 

 Itisbestpreci- But if, after having proceeded as I have just mentioned, 

 cohol a " ^ e i n * us i° ns °f cinchona reduced to the state of soft extract 

 be treated with alcohol, the greater part of the resiniform mat- 

 ter will be separated ; and nothing will remain but a brown 

 viscous substance, that has scarcely any bitterness, is per- 

 fectly soluble in water, and does not precipitate from it on 

 cooling. 

 Two different These experiments teach us, that in the infusions of these 

 principles m S p ec i cs f cinchona there are at least two very distinct sub- 

 stances: *one bitter and astringent, soluble in alcohol, and 

 but little soluble in water; the other on the contrary wholly 

 insoluble in alcohol, very soluble in water, and having a 

 sweet and mucilaginous taste, 

 in which most These substances being unquestionably those, which ope- 

 of Us virtue ra t e m0 st efficaciously in the diseases in which cinchona is 

 employed, I conceive it will not be superfluous to give an 

 account of their properties somewhat more at large. I shall 

 Properties of begin with that which is soluble in alcohol. 1. This sub- 

 that which is stance, in the dry state, has a brown red colour, and a very 

 h Qj U " bitter taste. 2. Cold water dissolves only one portion of it, 



another 



