Dr MacCulloch an Peat. 207 
Even in this case, however, long maceration and heat still ex- 
tract it. Another important remark on this subject was reserv- 
ed to this place. Wood- tar is highly soluble in acetic acid in 
all its states, and is also invariably mixed with a portion of 
free acid, which may be sepai’ated from it imperfectly by water, 
and more completely by the alkaline solutions ; after either of 
which operations it becomes more pitchy and tenacious. When 
this tar, therefore, appears to dissolve in water, it is in fact partly 
brought into solution by the acid. It is evident how this fact 
operates in comparing the solubility of peat with that of wood- 
tar ; since the dissipation and final disappearance of the acid 
from the former, must, in a corresponding degree, diminish the 
solubility of the hydrocarbonaceous compound. 
It does not appear that there are at present any further 
means of illustrating the chemical nature of pure peat, or the 
nature of the effects which are produced on the matter of vege- 
tables by the action of air and water, as far as the generation 
of that substance in its simple State is concerned. At this 
point also, the analogy between the effects of fire and of water 
appear to cease, since the application of the former agent has, 
in no direct experiment yet instituted for that purpose, produ- 
ced the results which follow the ulterior action of the latter. 
These results are, the change from peat into lignite, through 
all its stages, down to the bituminization of the vegetable mat- 
ter as it is found, nearly, if not absolutely, perfected in jet. 
To illustrate this part of the subject, it is necessary to con- 
sider the distinction between the bituminous substances, and the 
hydrocarbonaceous compound which constitutes the essence of 
peat, and to inquire by what tests the two can be distinguisli- 
ed. A method of making this distinction is required for tlie 
purpose of ascertaining, if possible, the point at which the pro- 
cess of bituminization commences; and, by the result of the 
inquiry, it will be seen, that there is an essential distinction be- 
tween peat and the bituminized woods, and that whatever con- 
fusion may appear between the two, follows from the admixture 
of both which occurs in certain states of the progress. 
The comparison between bituminous wood and peat will be 
rendered most easy, and the actual distinctions made more 
