Effects of Heat modified by Compression. 153 



Had the pressure been continued till all was cool, these sub- 

 stances must have been retained, producing a real coal. 



On the 24th of April 1803, a piece of leather used in a 

 similar manner (the compressing force being continued} 

 however, till all was cold) was changed to a substance like 

 glue, owing doubtless to compression, in a heat under that 

 of melting lead. 



These observations led me to make a series of experiments 

 with animal and vegetable substances, and with coal ; the 

 result of which I have already laid before the society. I shall 

 now repeat that communication, as printed in Nicholson's 

 Journal for October last (1804). 



" I have likewise made some experiments with coal, 

 treated in the same manner as the carbonate of lime : but 

 I have found it much less tractable ; for the bitumen, when 

 heat is applied to it, tends to escape by its simple elasticity, 

 whereas the carbonic acid in marble is in part retained by 

 the chemical force of quicklime. I succeeded, however, in 

 constraining the bituminous matter ox the coal, to a certain 

 degree, in red heats, so as to bring the substance into a 

 complete fusion, and to retain its faculty of burning with 

 flame. But I could not accomplish this in heats capable of 

 agglutinating the carbonate; for T have found, where I ram- 

 med them successively into the same tube, and where the 

 vessel has withstood the expansive force, that the carbonate 

 has been agglutinated into a good limestone, but that the 

 coal has lost about half its weight, together with its power 

 of giving flame when burnt, remaining in a very compact 

 state, with a shining fracture. Although this experiment 

 has not afforded the desired result, it answers another pur- 

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

 is crossed by a dike of whinstone, the coal is found in a pe- 

 culiar state in the immediate neighbourhood of the whin ■ 

 the substance in such places being incapable of giving flame 

 it is distinguished by the name of blind coal. Dr. Mutton 

 has explained 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 probablv be re- 

 tained by distillation. Yet the whole must nave been car- 

 ried 



