212 
Dr MacCulloch on Peat, 
sure to the action of the cause by which the change in the vege- 
table compound was induced. It is probable that the peat 
found under alluvial soils Avill be more highly bituminized than 
when it occurs in superficial beds; as in most cases it will, in 
these situations, be a more ancient deposit ; but as yet no op- 
portunities for making the requisite trials have been aiforded. 
It is impossible, by direct experiments, to prove that water, 
or the action of water and air combined, is capable of changing 
vegetable matter into bitumen, as the necessary element of time 
cannot be introduced into such experiments. It may, however, 
be inferred, with a considerable degree of probability, from 
analogical observations. It has already appeared that the essen- 
tial distinction between the bitumen and the products of vege- 
table distillation, consisted in the predominance of oxygen in 
the latter class of substances. Apologizing for a little laxity in 
the use of the term, the process of bituminization must therefore 
be considered as a deoxydation of the vegetable matter. Now, 
when turpentine is converted into resin by the action of air, or 
of air and water, not only the proportions of hydrogen and car- 
bon are changed, but it no longer yields on distillation the same 
quantity of acetic acid. A species of deoxydation has here 
therefore taken place, and analogous effects appear to result 
from the action of the same causes on the liquid bitumens, and 
on vegetable tar. It was also shewn that peat yielded less acid 
on distillation than unchanged wood, so that the action of water 
in this case also, has the power of deoxy dating the vegetable 
matter, as well as of dissipating a portion of the hydrogen 
which it contains. It is not unreasonable to conclude, that it 
may, by a continuance of the same action, produce the ultimate 
change into bitumen. The changes which it is capable of effect- 
ing on the fibrous parts of animal matter, by converting them 
into adipocire, if they do not present a very exact analogy, at 
least indicate a power adequate to the production of effects more 
complicated and less to be anticipated. 
It has been asserted that vegetable matter was converted in- 
to bitumen by the action of fire ; and, in extending this theory 
to the formation of coal, some experiments have been adduced 
in support of its truth These consisted in heating vegetable 
Sir James Watt’s experiments. 
