EFFECTS OF HEAT. \Q3 



and where the veflel has withftood the expanfive force, that 



the carbonate has been agglutinated into a good lime-ftone, but Remarkable fa£l 



, ,n • ■ 1 1 • 1 - of a Droduttion 



that the coal has loft about half its weight, together with «ts refembling 

 power of giving flame when burnt, remaining in a very com* blind coaU 

 pad ftate with a (hining fra6ture. Although this experiment 

 has not afforded the defired refult, it anfwers another purpofe 

 admirably well. It is known that where a bed of coal is crofled 

 by a dyke of Whinftone, the coal is found in a peculiar ftate 

 in the immediate neighbourhood of the Whin, the fubftance in 

 fuch places being incapable of giving flame, it is diftinguiftied 

 by the name of blind coal. Dr. Hutton has explained this 

 fad by fuppofing that the bituminous matter of the coal has 

 been driven by the local heat of the Whin into places of lefs 

 intenfity, where it would probably be retained by diftillaiion. 

 Yet the whole muft have been carried on under the aftion of a 

 preflTure capable of conftraining the carbonic acid of the calca- 

 reous fpar which occurs frequently in fuch rocks. In the laft 

 mentioned experiment, we have a perfe6t reprefentation of the 

 natural fad lince the coal has loft its petroleum, whilft the chalk 

 in contad with it has retained its carbonic acid. 



I have made fome experiments of the fame kind with ve- Animal and ve- 

 getable and animal fubftances. I found their volatility much f^uttreTted?'* 

 greater than that of coal, and I was compelled with them to 

 work in heals below rednefs; for even in the loweft red heat 

 they were apt tadeftroy the apparatus. The animal fubftance 

 I commonly ufed was horn, and the vegetable faw-duft of fir. 

 The horn was incomparably the moft fuftble and volatile of the 

 two. In a very flight heat it was converted into a yellow red 

 fubftance like oil, vvhicli penetrated the clay lubes through and 

 through. |n thefe experiments I therefore made ufe of tubes 

 of glafs. It was only after a confiderable portion of the fub- 

 ftance had been feparated from the mals that the remainder af- 

 fumed the clear black peculiar to coal. In this way I obtained 

 coal, both from faWrduft and from horn, which yielded a bright 

 flame in burning. 



The mixture of the two produced a fubftance having exadly ProbabiHty that 

 the fmell of foot or coal tar. I am therefore ftrongly inclined ^^^^ ^^ ^^ ammat 

 to believe that animal fubftance, as well as vegetable, has con- j^ble origin. 

 tributed towards the formation of our bituminous ftrata. This 

 feems to confirm an opinion advanced by Mr. Keir, which has 

 l}een mentioned, to n)e fince I made this experiment. I con- 

 ceive 



