•5<;i XJbftrvatlons and Experiments on ElaJ}ic Bitumen, 



from a partial and minute dif-union or difintegracion of the particles of the original fiibfknct, 

 as both fpecies melt into one whiclj is perfedlly fiinilar. I muft alfo add, that the fpecies A 

 burns cafily, and with rapidity ; but the fpecies B burns with fome difficulty, and crackles as 



'if it had imbibed a quantity of water. 



I have remarked, when the different varieties of the elaftic bitumen were melted, that they 



-completely loft the claftic property, and a quantity of air or gas appeared to be difenga^ed, 

 particularly from the fpecies B. I alfo obfcrvtd, that the fubftanccs which remained after 

 this operation, correfpondcd, in refpeil to confiftence, with thofe which had been employed, 

 as the following table will fhevv : 



A, No. 7 and 8 produced a thick h'quid petroleum, not apparently different from that 



which is commonly known. 

 A, No. 9 produced a thicker petroleum, approaching to mineral tar. 



A, No. 1 1 and I2 . . . produced mineral tar. 



B, No. 6 produced the fame, approaching to mineral pitch. 



A, No. 13 produced mineral pitch. 



A, No. 14 and 15 .. . did not fuffer any change, but remained as at firft, with all the cha- 



rafters of afphaltum. 



From what I have related, I fufpe£t that the elaftic property is occafioned by the inter- 

 vpofition of very minute portions of air or fome other elaftic fluid between the parts of the 

 bitumen, and that this takes place by reafon of iCcnQ unknown caufc at the time of forma- 

 tion ; but when thefe bitumens are melted, the elaftic fluid is liberated, and the mafs lofcs 

 that fine fpongy texture which I fufpect to have been the caufe of the elaftic property *. 



Derbyfhire is well known as a country which exhibits, in the moft ftriking manner, the 

 remarkable changes which our globe 'has fufFered. In every part of it, the moft indifpatablc 

 evidences appear of fome great and extraordinary revolution j and there is not any place 

 where extraneous foffils, fuch as the remains and imprefftons of vegetables and animals, arc 

 more abundant. 



Bitumen, in other countries, is moft commonly found where thefe prefent themfelves; 

 and, in like manner, there are few countries which abound fo much with bitumen as Derby- 

 {hire. 



Whoever has examined the limeftone rocks about Matlock, and moft other, places in this 

 county, muft be convinced of the truth of this aflertion. 



The limeftone and calcareous fpars alfo, where the elaftic bitumen is found', are, for the 

 greater part, in the fameftate ; fo that no doubt can be entertained but that this bitumen has 

 had the fame origin as thofe which are more generally known ; and it would undoubtedly 

 have been confounded with them, had it not been difcovcred when paffing from the liquid 

 to the folid ftate. 



* The elaftic bitumen, A, No. 9. when digeflcd in fulphuric ether in a temperature of about 55°, is partly 

 diffolvcd. The folution is yellowiih brown when oppofed to the light ; but, vvhen otherwife viewed, is lil^c 

 the bitumen, that is, of a browniih olive colour. By fpontancous evaporation, the etheric folutJon leaves a 

 yeliowilb brown bitumen, which is totally devoid of elafticity. The undilTolved portion (like the cahout-efeou 

 under fimilar circumflances; is foftened, and is much increafed in bulk. 



The fpecies B, No. 6. cut into very thin flices, communicates a yellow tinge to fulphuric ether j in other 

 refpefts It is but Ihtle affefted. 



The 



