198 ACTION 0-f HEAT MOPIFIEB 



matter of the leather which escaped from the outward parts, 

 had within the rim, been constrained to remain united to 

 the rest of the composition, upon which it had acted as a 

 flux, and' the whole together had entered into a liquid state, 

 in a very low heat. Had the pressure been continued till 

 all was cool, these substances must have been retained, pro- 

 ducing a real coal. 

 Direct expcri- On the 24th 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.)* Vy, 



ecTtrhe^t un-' " ^ ^^'^ likewise made some experiments with coal,treated- 

 Aet conipres- ^ " -- manner as the carbonate of lime : but I have found 



sion. it much less tractable ; for the bitumen, when heai :.■ >, plied ■ 



to it, tends to escape by its simple elasticity, whereas the.CAr--, 

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

 of quicklime. I succeeded, however, in constraining the bitu- 

 minous matter of the cx)al, 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 I 

 have found, where I rammed 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 com- 

 pact state, with a shining fracture. Although this experiment 

 has not afforded the desired result, it answers another purpose 

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



tho volatile , , ^■^ c ^ • I , . ^ 



matter escaped crossed by a dike of whmstone, the coal is found in a peculiar 

 a production gtatc in the immediate neighbourhood of the whin : the sub- 



* As the present extract is short, it was thought better to repeat 

 it here, than to interrupt the subject by referring to our ixth volume. 

 , Ed. 



• . ' stance 



