SY COMPRESSION?, ^ IQQ 



Stance in such places being incapable of giving flame, it is dis- I'eflenjblin^ 



/• !»• J T-. TT L blind coalwas 



tinguished by the name of bund coal. Dr, Hutton has ex- afforded. 



plained this fact, by supposing that the bituminous matter of 

 the coal, has been driven by the local heat of whin, into places 

 of less intensity, where it would probably be retained by distil- 

 lation. Yet the whole must have been carried on under the 

 action of a pressure capable of constraining the carbonic acid 

 of the calcareous spar, which occurs frequently in such rocks^ 

 In the last-mentioned experiment, we have a perfect represen- 

 tation of the natural fact ; since the coal has lost its petroleum, 

 while the chalk in contact with it has retained its carbonic 

 a^id. 



" I have made some experiments of the same kind, witbAmtwal an*! 

 vegetable and animal substances. I found their volatility i^uch ^ *^^*j^3^g™*jj' 

 greater than that of coal, and I was compelled, with them, tothe same maiv- 

 work in heats below redness ; for, even in the lowest red-heat, "'''^* 

 they were apt to destroy the apparatus. The animal substance 

 I commonly used was horn, and the vegetable, saw-dust of fir. 

 The horn was incomparably the most fusible and volatile of 

 the two. In a very slight heat, it was converted into a yellow- 

 red substance, like oil, which penetrated the clay tubes through 

 and through. In these experiments, I therefore made use of 

 tubes of glass. It was only after a considerable portion of the 

 substance had been separated from the mass, that the remain- 

 der assumed the clear black peculiar to coal. In this way I 

 obtained coal, both from saw-dust and from horn, which yield- 

 ed a bright flame in burning. 



** The mixture of the two produced a substajice having ex- it is probable 

 actly the smell of soot or coal-tar. I am therefore strongly in- ^^^^^ as™geS- 

 clined to believe, that animal substance, as well as vegetable, ble matter has 

 has contributed towards the formation of our bituminous p^^*^lj.y^-jj*°g 

 strata. This seems to confirm an opinion, advanced by Mr. strata. 

 Keir, which has been mentioned to me since I made this ex- 

 periment. I conceive, that the coal which now remains in the 

 world, is but a small portion of the organic matter originally 

 deposited : the most volatile parts have been driven off by the 

 action of heat, before the temperature had risen high enough to 

 bring the surrounding substance into fusion, so as to confine the 

 elastic fluids, and subject them to compression. 



*'In 



