Oh/ervatkns tn the ElaJlUliy df Bltumm, 5}e| 



SPECIES THE SECOND. 



B, No. I. — Elaftic bitumen, which, recently cut, cxadlly refembles fine clofe cork in 

 colour and texture, but, by the air, in a few days it becomes of a pale reddifh brown.— This 

 forms a thin coat, which completely covers a mafs of elaftic bitumen, which is foft, and of 

 a brownifti olive colour, like A, No. 9. 



B, No. 2. — ^The fame, excepting that the coat or cruft is much thicker. 



B, No. 3. — ^The fame, but the coating is thicker than that of No. 2, and the brownifh 

 olive-coloured bitumen much lefs in quantity. 



B, No. 4.— The fame, excepting that the greater part of the mafs refembles cork, fo that 

 only a very fmall nucleus of the brown bitumen remains *. 



B, No. 5. — The fame, excepting that the bitumen, which is coated, is in the ftate of 

 afphaltum. The fpecific gravity of this fpecimen is 0,9881. 



B, No. 6. — Elailic bitumen, the whole mafs of which refembles fine cork. — The fpecific 

 gravity is 0,9748. 



B, No. 7. — The fame, but friable, and apparently paffing by decompofition into an 

 ochraceous coloured powder. 



THE varieties of the firft fpecics of the elaftic bitumen, or that which is like the cahout- 

 'chou, evidently appear to be formed from a naptha or petroleum, which, like that which pro- 

 duces the other fimple bituminous fubftances formerly mentioned, is fufceptible of various 

 degrees of infpiflation. 



All the varieties of the firft fpecies, from No. i, to No. 15, may be regarded as thus form- 

 ed ; for in thefe we can trace all the modifications comprehended between petroleum and 

 afphaltum : with this difference, that the intermediate modifications of this fpecies have the 

 remarkably property of elafticity which is the moft complete in the variety which occupies 

 the middle place between petroleum and afphaltum. 



The fecond Ipecies B, or that which resembles cork, appears fo different from that marked 

 A, that it is not at firft eafy to conceive how they are connected, or at leaft the difficulty 

 muft appear great to thofe who have only feen fpecimens of each fpecies complete in their 

 refpe£tive charailers. But, from an attentive examination of many fpecimens, and particu- 

 larly of thofe which I have defcribed, I am convinced that the varieties of the fpecies B are 

 only modifications of the fpecies A, produced probably by long maceration in the water of 

 the rivulet in which this fpecies is found, to the effects of which we may, with fome appear- 

 ance of reafon, add the viciffitudes of the feafons, of air, and of the weather in general, as 

 well, as thofe of reiterated moifture and drynefs occafioned by the rife and fall of the water of 

 the rivulet -, and what feems to corroborate this opinion is, that the fubftance, like cork, in- 

 crufts the fpecies A, and appears to be only a change which has penetrated deeper into the 

 fubftance of it in proportion to the duration of the caufes which I have mentioned, fo that at 

 length the original fubftance no longer remains in its primitive ftate. I do not believe, 

 however, that this change arifes from any alteration in the conftituent principles, but merely 



* Oue ef the fpecimens in my poffeflion, fimikr toB, No. 4, weighs between 13 and i4pouads. 



K k 2 feoia 



