£04 
Dr MacCulloch on Peat. 
ammonia, often very minute, is also found, and this, as might 
be expected, is combined with the acid. When the process is 
irregularly conducted, a second process is carried on together 
with the first, and the new compounds become partially decom- 
posed. Thus there is produced a gaseous substance, which is 
either hydrocarbonic gas, containing various proportions of car- 
bon, or else a^ mixture of that gas and carbonic oxide. At 
times, according to the mode in which the process has been con- 
ducted, no essential oil is obtained, the whole of it being decom- 
posed as fast as it is formed, and recompounded into the hydro- 
carbonic gas. But it may be procured by redistilling the tar, 
which thus becomes separated by a further decomposition into 
essential oil, pitch, and a fresh proportion of acetic acid, always 
holding, from its strong affinity to that substance, a portion of 
the inflammable compound in solution. The pitch, by continu- 
ing this process, at length loses its character, and becomes a 
brown or black friable mass, but still continues to give over vo- 
latile inflammable matter and acid, until it is finally reduced to 
the state of charcoal; Finally, it gives over hydrogen only, and 
acquires an extreme degree of hardness, as ordinary charcoal 
does in tlie same case, becoming also unsusceptible of further 
change. It may be remarked, that as the tar becomes pitchy, 
the essential oil, which was originally pale, and at first nearly 
colourless, becomes gradually darker, and that the volatile pro- 
duct of the solid pitch is not oil but tar, which is, however, ca- 
pable of being decomposed in a similar manner by a repetition 
of the same treatment. It is obvious, that this is the conse- 
quence of the greater heat required in this case, to eflect the se- 
paration of the volatile product. 
In reconsidering the consequences of thus pushing the process 
touts extremity, it is apparent that the whole vegetable matter 
is or may, by further analysis of the acetic acid and the ammo- 
nia, be resolved into carbon, hydrogen, oxygen, and azote; 
that the proportions of these might, by a more laborious and ac- 
curate analysis, be discovered, and that they may be conjectured 
with sufficient accuracy for the purposes now in view, by attend-^ 
ing to the several proportions in which these compounds are ob- 
tained. 
