or ElaJJic Bitumen of Derhv/h'tre, 229 



Section I. 



Comprejjlble Bitumen. 



Variety T. Elaftic bitumen of a blackifh brown and fome- 

 what olive colour, foft, exceedingly comprefliblc, unAuous 

 and fomewhat fat, of a fligblly aromatic fmcll, but having 

 a little of the infipid odour of natural caout chouc; inflam- 

 mable, and burning with a bright brilliant flame, leaving a 

 black oily refiduum which does not become dry. The frag- 

 ments of this variety are fometimes an inch and a half in 

 thicknefs and four inches in breadth. Thev are the largeft 

 except the fragment ia poirellion of Mr. Mawe, which is 

 confiderably larger. 



Variety If. Foffil caout-chouc, fplit and cracked in the 

 whole exterior furface, which was in contact with the matrix 

 from which it has been detached. It is dry in that pari, but 

 neverthelefs compreffible ; black on the furface expofcd to 

 the contaA of the air; but remarkable in this refpetl, that 

 when a lamina of about a line in thicknefs is cut from this 

 caout-chouc with a very fliarp knife, it appears in the infide 

 of a yellowilh white colour : when cut in a very thick part, 

 where the aftion of the air has not been able to render it 

 black, like certain balls of the elaflic gum brought fometimes 

 from Para, it has the fame appearance as the ufual caout- 

 chouc. Another circumllance worthy of attention is, that 

 in the part recently cut a kind of acid matter is obferved to 

 ooze out, which is not of a difagreeable talle, and which ap- 

 pears to be of the nature of the pyrolignic acid. This caout- 

 chouc is pellucid on the edges, and almofl of a hyacinth red 

 colour. 



Scarcely has the air exercifed its aolion on the part re- 

 cently cut, which is white, when it aflumes a flight reddifh 

 tint, which daily becomes darker, and acquires a dark maho- 

 gany and then a blackifli brown colour; at length, at the end 

 of a month, if expofcd to the air, it becomes of a deep black. 



Variety III. The fame caout-chouc as the preceding, but 

 of a fomewhat firmer texture and a ligneous appearance. 

 When viewed with a magnifying glafs, it is obferved that the 

 fibrous undulations feen in this variety are merely the efie6t 

 of the milky fubftance which flowed from the tree more or 

 lefs flovvly or at different times, and which did not acquire 

 confiflence till it had loll the mucilaginous water which held 

 the matter of caout-chouc fulpended or in folution. I par- 

 ticularly mention this facM, to (liow that this variety has no 

 real relation to the word of the tree which produced at that 

 period the claflic bitunicu. 



O 3 Variety 



