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Bitumen alone would not, however, accomplish that grand pur- 
pose for which nature formed coal ; that of supplying future ages 
with a substance for fuel, which, by a moderate exercise of the 
ingenuity of man, might be made to burn with almost every degree 
of intensity ; from that which is employed to convey to the human 
body a grateful sensation, to that which is necessary to fuse some 
of the untractable metals. 
The rapidity with which pure bitumen burns, would not only 
occasion a considerable waste of it, if it were attempted to be 
employed for the purposes to which coal is applied; but would 
also render it so unmanageable, as entirely to prevent its useful 
application, to even the most ordinary purposes which coal is in- 
tended to fulfil. 
To moderate this high degree of combustibility, and so to regu- 
late it, that the consumption of a substance, so necessary to man, 
should be rendered uniform and economical, was therefore required. 
To accomplish this, the intermixture of some incombustible sub- 
stance with the bitumen became necessary. But to produce those 
characteristic properties, by which coal is distinguished from all 
other substances of the same class, a particular kind of arrange- 
ment of the particles of this heterogeneous mass was requisite. It 
was necessary that the bituminous particles should be so involved, 
and insulated, on every side, as to be nearly defended from the 
action of the fire. It was also necessary that the regularity of its 
combustion should not be disturbed, by the superadded incombus- 
tible matter existing in the mixture, in such gross particles, or in 
so irregular a state of diffusion, as would have been the case, if the 
earth had remained in it, in the state in which it had subsided along 
with the sunken vegetable mass. 
The arrangement of the respective particles of the mass, which 
would make the nearest approach to the attainment of the required 
object, would be that in which each individual particle of bitumen 
