MODIFIED by COMPRESSION. 151 



the refult of which I have already laid before the Society. 

 I fhall now repeat that communication, as printed in Nichol- 

 son's Journal for October laft (1804). 



" I HAVElikewife madefome experiments with coal, treated 

 in the fame manner as the carbonate of lime : but I have found 

 it much lefs tradable ; for the bitumen, when heat is applied 

 to it, tends to efcape by its fimple elafticity, whereas the car- 

 bonic acid in marble, is in part retained by the chemical force 

 of quicklime. I fucceeded, however, in conftraining the bitu- 

 minous matter of the coal, to a certain degree, in red heats, fo 

 as to bring the fubftance into a complete fufion, and to retain 

 its faculty of burning with flame. But, I could not accomplifh 

 this in heats capable of agglutinating the carbonate ; for I 

 have found, where I rammed them fucceflively into the fame 

 tube, and where the veflel has withflood the expanlive force, 

 that the carbonate has been agglutinated into a good limeftone, 

 but that the coal has loft about half its weight, together with 

 its power of giving flame when burnt, remaining in a very 

 compact ftate, with a mining fracture. Although this experi- 

 ment has not afforded the delired refult, it anfwers another 

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

 is crofted by a dike of whinftone, the coal is found in a pecu- 

 liar ftate in the immediate neighbourhood of the whin : the 

 fubftance in fuch places being incapable of giving flame, it is 

 diflinguifhed by the name of blind coal. Dr Hutton has ex- 

 plained this fact, by fuppofing that the bituminous matter of 

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

 of lefs intenfity, where it would probaBly be retained by diftil- 

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

 action of a preffure capable of conftraining the carbonic acid 

 of the calcareous fpar, which occurs frequently in fuch rocks. 

 In the laft-mentioned experiment, we have a perfect reprefen- 



tation 



