172 A BOTANICAL DLSCIUPTION OF 



The Urceola eaout-chouc, rubs out the marks of a 

 black lead pencil, as readily as the American, and is 

 evidently the fubitance of which the Chinefe make 

 their elaltic rings. 



'b v 



It contains much combultible matter, burning en- 

 tirelv away, with a clear flame, emitting a coniidera 

 ble deal of dark-coloured fmoke which readily con- 

 denfes into a large proportion of exceeding fine foot, 

 or lamp-black \ at the fame time it gives but little 

 fmell, and that not difigrceable ; the combuition is 

 often fo rapid, as to caufe drops of a black liquid, 

 very like tar, to fall from the burning mats ; this is 

 equally inflammable with the reft, and continues 

 when cold in its ferni-fluid itate, but totally void of 

 elasticity ; in America the caout-chouc is ufed for 

 torches, ours appears to be equally fit for that pur- 

 pofe. Expofed m a lilver lpoon to a heat, about 

 equal to that which melts lead or tin, it is reduced 

 into a thick, black, inflammable liquid, fuch as drops 

 from it during combuition, and is equally deprived of 

 'tis elaftic powers, confequently rendered unfit for 

 thole purpofes, for which its original elafticity ren- 

 dered it lo proper. 



It is inlbluble in fpirits of wine, nor has water any 

 more effect on it, except when aililted by heat, and 

 then it is only foftened by it. 



Sulphuric acid reduced it into a black, brittle, 

 charcoal like fubitance, beginning at the furface of 

 the caout-chouc, and if the pieces are not very thin, or 

 fmall, it requires fomc days, to penetrate to their cen- 

 tre; during the proceis, the acid is rendered very dark 

 coloured, almoft black. If the fulphuric acid is pre- 

 viouflv diluted, with only an equal quantity of water, 

 it does not then appear to have any effect on this fub- 



nce, nor is the colour of the liquid changed thereby. 



Nitric 



