The Middlebury register. [volume] (Middlebury, Vt.) 1850-1882, 1870-06-21
Deterioration of Coal by Exposure ia
the Air.

Very few articles on this importan
subject have appeared in our scientii,
journals, and it is only within few year
that the attention of engineers has beer
called to the great loss suffered by Goa
from exposure in the open air. Recent
ly German chemist, DR.. T.. Richtcrs
has been studying the question, and ha.
given the world the benefit of his obser
vations. 1t appears that coal at ordin
ary temperatures, absorbs oxygen ant
it it be heated to 390' F., it at first in
creases in weight, carbonic acid and wa
ter are expelled, and oxygen absorbed
until the oxygen and hydrogen are in the
proper proportions to form water.
The carbon in the coal appears to b,
present in two notifications, one of which
is not well understood and it is comprised
under the general name of bitumen. The
bitumen carbon is first oxidized, and the
other modification is the last to be affect.
ed. The amount of microscopic water
that the coal can absorb varies considerably
and does not appear to be dependent upon
the structure ofthe coal. Solid coal absorbs
not unfrequently, three times as much
water as softer, more amellar article
The changes that take place in the coal
are naturally more rapid in the early
stages of its exposure than at later
period, but the absorption of oxygen doe
not cease at any time. Ifa current of
air is passing over coal heap, large quan.
titles Of carbonic acid will be given off ;
but where the air is quiet,the coal absorbs
the carbonic acid and less change is man.
ifest According to this, on windy DAYS
the loss in the weight of coal must be
crater than when the weather is calm
The temperature of the air has much
to do with the deterioration of coal, as
warm weather greatly promotes the alb
sorption OF oxygen and the formation of
carbonic acid. All engineers agree that
the influence Of moisture is very great
Water operates in various ways; it acts
upon the iron pyrites, that in greater or less
quantity accompanies all coal, vAidises
the iron, slakes the coal, and thus exposes
crater surface to the action Of the air.and
heats up the mass, so as to promote oxid-
alton. The sulphate Of iron in turn oxi-
dies, and is again reduced by the coal !;
and it is thought that the green vitriol
thus serves as Il conveyancer of oxygen
to the coal and occasions its combustion,
This fact has been overlooked in account
ing for the large loss in the value OF coal.
Whether sunlight has any influence
upon the decomposition and oxidation of
coal is uncertain. All Of the observations
were contradictory, hut perhaps a major
ity of them authorize the conclusion that
sunlight prevents the destruction of coal.
The spontaneous combustion of coal is
a matter of great importance, and has
been the special object of study, but it is
difficult to give satisfactory explanation
OF it. By some observers it is attributed
to species Of molding,such as moist h~y
undergocs, thus giving rise to sufficient
iron pyrltcs, but IA closer study OF the sub
ject has shown that 1902 Fab is the ut
most that can be anticipated from this
cause.
The most rational explanation appears
to be the absorption Of oxygen and the
rapid oxidation of the carbon-thc more
rapid the oxidation the crater the increase
OF heat, until Il temperature is reached
that sets fire to the heap Of coal. The
conditions that favor the spontaneous ig-
milton Of the coal are, great exposures OF
surface, fine structure of the coal. in pill
ing in large heaps, and moisture.
There appears to be no doubt that the
loss in the wei ght and heat-producing
value of coal is very great, whenever it is
exposed to the action of the atmosphere
in large heaps, and it is better not tc
keep such stock on hand as is done by
many establishments. Aside from the
loss in weight, there is IA manifest detcri'
alton in its heating power, occasioned by
the liberation of much Of the hydrogen
and the consumption of the bitumen mod
i6cation of carbon. Coal freshly mined
is more valuable as fuel, and it is wortf
more per tun than the heaps that have
been dcteriorated by long exposure to thu
air.