MODIFIED by COMPRESSION. 151 
the refult of which I have already laid before the Society. 
I fhall now repeat that communication, as printed in Nicnot- 
son’s Fournal for October laft-(1804). 
“ I wave likewife made fome experiments with coal, treated 
in the fame manner as the carbonate of lime: but I have found. 
it much lefs tractable; 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 L 
have found, where I rammed them {ucceflively into the fame 
tube, and where the veflel has withftood the expanfive 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 fhining fracture. Although this experi- 
ment’ 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 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 
diftinguithed by the name of blind coal. Dr Hurrow 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 haye a. perfeét reprefen- 
tation. 
