40 , Esperimcnts en Caoui-ihouc, or Indian Ruhler, 



The Urccok caout-chouc, rubs out the marks of a black lead pencil, as readily as 

 the American, and is evidently the fubftance of which the Chinefe make their elaftic 

 -rings. 



It contains much combuflible matter, burning entirely away, with a clear flame, 

 emitting a confiderable deal of dark-colourcd fmoke which readily condenfes into a 

 large proportion of exceeding fine foot, or lamp-black ; H the fame time it gives but 

 little fmell, and that not difagrecable ; the combuftion is often fo rapid, as to caufe drops 

 of a black liquid, very like tar, to fall from the burning inafs ; this is equally inflam- 

 mable with the reft, and continues when cold in its femi-fluid ftate, but totally void of 

 elafticity ; in America the caout-chouc is ufed for torches, ours appear to be equally fit 

 for that purpofe. Expofed in a lllver fpoon 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 combuftion, aid is equally tleprived of its elaftic powers, confequently rendered 

 unfit for thofe purpofes, for which it* original elafticity rendered it fo proper. 



It is infoluble in fpiTit> of wine, nor has water any more effeft on it, except when 

 afljfted by heat, and tl"ic;i it is only foftened by it. 



Snlphurifc acid reduced it into a black, brittle, charcoal like fubftance, beginning at 

 the furface of the caout-chouc, and if the pieces are not very thin, or fmall, it requires 

 foir.e days to penetrate to their centre ; during the procefs, the acid is rendered very dark 

 coloured, almoft black. If the fulphuric acid is previoufly diluted, with only an equal 

 quantity of water, it does not then appear to have any cffc£i on this fubftance, nor is 

 the colour of the liquid changed thereby. 



Nitric acid reduced it in twelve liours to a foft, yellow-, unelaftic mafs, while the acid 

 is rendered yellow ; at the end of two days, the caout-chouc had acquired fome degree 

 of friability and hardnefs. The, fame experiment made on American caout-chouc was 

 attended with fimilar effe£ls. Muriatic acid had no efFeft on it. 



Sulphuric aether only foftened it, and rendered the different minute portions it wal 

 eut into eatily united, and without any feeming diminution of elafticity. 



Nitric aether I did not find a betwr mentftruum than the vitriolic, confequently, if the 

 aether I employed was pure, of which I have fonle doubt-, tltis fubftance muft differ 

 fffeatially from that of America^ which Berniard reports to be foluble in nitric 

 aether. 



Where this fubftance can be had in 4 ffntd ftate, there is no necefTity for diffolving 

 or foftening ic, to render it applicable to Ihe various uf«s for which it may be roquired;; 

 but where the dry caoilt-chouc is only procurable, fblphuric aether promifes to be an 

 ufeful medium, by whkh it ihay be rendered fo foft as to be readily formed intb'a 

 variety of Ihapes. 



Like American awUt-chduc, it is;foi\li)lie in the effential oil of turpantine, and rfiml 



n 



