21Q Dr MacCulloch on Peat. 
change is a change of proportion between the hydrogen and 
carbon, which constitute the chief part of their bulk ; and that 
the action of the atmosphere consists in dissipating, in a manner 
not yet understood, a portion of the former substance, so as to 
increase the relative quantity of carbon. It is not, in fact, dissi- 
milar in its effects to the action of ffre. 
In attempting to apply this knowledge for the purpose of di- 
stinguishing peat from lignite, or of ascertaining the progress 
of bituminization, it will be evident, that from the identity of 
the products obtained by destructive distillation, and the diffi- 
culty of ascertaining minute differences in their proportions, no 
satisfactory results can be derived from examining these propor- 
tions, in cases where the change is incipient, where, in effect, 
there is a mixture of peat and bituminiz^d matter. In the last 
stages, the differences become more palpable, and in the case of 
jet, which is the most perfect of the lignites, they are abundant- 
ly sensible. But the test of naphtha may be applied to the ex- 
amination, either of the oil procured by the distillation of peat, 
in its progress to bituminization, or to that obtained from the lig- 
nites. By means of this fluid, the mixed oil is separated ; that 
which is produced From the peat or unchanged vegetable mat- 
ter being rejected, while that which proceeds from the bitumi- 
nized vegetable matter is dissolved. A tolerable conjecture can 
thus be formed of the degree in which the progress of bitumini- 
zation has taken place ; and, when considerable, it is generally 
also sensible in the smell of the oil, which resembles that produ- 
ced by mixing naphtha with the oil of wood. The peculiar 
smell which some peat gives in combustion, arises from this 
cause, and indicates the commencement of bituminization. 
In thus examining the various kinds of submerged vegetable 
matter to which we have access, the progress of bituminization 
may be traced, with little interruption, from peat, through sub- 
mergnd wood, brown coal, and surturbrand, down to jet, the 
most perfectly bituminized substance still retaining its organiza- 
tion, with which we are acquainted. That which I have cho- 
vSen to consider as pure peat, gives no traces of bitumen ; jet, on 
the contrary, gives very minute indications of the products ob- 
tained from unchanged vegetable matter. The state of the 
submerged papyri offers an mtcrestiiig example of the progress 
