Professor Harkness on Coal. 7" 
this’ a greater amount of hydrogen than obtains in ordinary coals, 
and this greater amount of hydrogen must have arisen from this 
principle, as continued in the original tissues of the plants which 
have furnished the organic elements of this substance ; and this cir- 
cumstance leads us to conclude that the vegetable matter forming 
cannel has been less subjected to chemical decomposition than that 
in ordinary coals. The aspect of this substance, which is generally 
less shining also, supports the inference that the amount of 
change produced on the organic constituents is less than usually 
prevails in other coals, and therefore we must regard cannel as being 
the result of vegetable matter which retains more of its original con- 
stituents than other coals. As respects ordinary coals, these are 
intermediate in their character, so far as regards hydrogen, between 
the cannel and the anthracites. They seem to have parted witha 
considerable portion of their hydrogen, as this originally formed 
portions of the plants from which coal is derived ; and hence we have 
them possessed of different properties and amount of constituents, in 
some instances affording a considerable amount of hydrogen, and in 
others only a small quantity, approaching in their nature to the 
anthracites, where we have the hydrogenous principle developed only 
to a very small extent. 
Taking, therefore, the elemental principle hydrogen, as a crite- 
rion from which to draw deductions concerning the state in which 
the vegetable matter forming this substance is, we should infer that 
in those which retained the greatest amount of this we have the 
tissues nearest their original condition, and we should consequently 
conclude that in cannels this vegetable matter is nearest its original 
state ; while in ordinary coals it is more changed, and in anthracites it 
has so far lost its original character as to retain but a small portion of 
_this principle. The result of this loss of hydrogen, and the change 
which the vegetable matter would undergo consequent thereon, would 
induce us to expect that compression would be varying in its effects in 
proportion to the modification which the vegetable matter has been 
subject to, more particularly when no mineral matter has supplied 
the place of the organic constituents of the vegetables, a circumstance 
which seems to have been ordinarily the case with coals. In can- 
nels, therefore, and in other coals abounding in hydrogen, where the 
constituents of the plants are nearest their original state, and where 
we may infer that the cellular structure has only been in part obli- 
terated, the effects of compression on this would be less than when 
the vegetable matter had so far changed its nature as to be almost 
converted into carbon. We may therefore infer that the results of 
compression would be modified according to the condition of the sub- 
stance compressed ; and taking this as a means of judging of the state 
and effects of compression, we might conclude that cannel was better 
able to resist compression than ordinary coals, and that, consequently, 
the effects produced thereby are less than on this form of fossil fuel, 
a conclusion which we shall find some matters connected with this 
