The Liverpool Standard and General Commercial Advertiser.
Liverpool, Merseyside, England, 1844-06-11 00:00:00

LIVERPOOL POLYTECHNIC SOCIETY.

On Tuesday, the 14th ult., Mr. D. Waldie delivered
the second part of a communication on Flame and its prac-
tical relation to Light, Heat, and Smoke, with special
relation to the Combustion of Coal, of which the follow-
ing is a brief abstract : _ _

He commenced by a brief recapitulation of the first part
of the communication delivered at the previous monthly
meeting. Combustion was defined to be an act of chemi-
cal combination of such intensity as to be productive of
heat and light, and flame was such a process taking place
between two bodies both in the gaseous state. Two sub-
stances of opposite chemical affinities were necessary to
this process ; and though one class were usually called
combustibles, and another, such as air or oxygen, sup-
porters of combustion, there was no real distinction be-
tween the two, the difference being only circumstantial,
both being alike combustibles, and each a supporter of
the combustion of the other.

In gaseous combustion, combination always takes place
between definite proportions of the two substances, and
may be affected either between the two gases previously
mixed, or during the spontaneous mixture which takes
place when one gas flows into another. In the latter case,
the various circumstances of density, combining propor-
tion and composition of the two gases, influence the form,
size, and appearance of the flame.
Light gases, which possess great diffusibility or tendency
to spread through others, form large flames when they
burn in an atmosphere of heavier gas, and vice versa.
Again, when one gas requires a much larger volume than
its own of another to combine with it, when the former
flows into an atmosphere of the latter, it forms a large
flame, requiring to spread far through it ; when the cir-
cumstances are reversed, a small flame is the result.
In such cases, when simple gases are employed, or even
some compound ones, the flame consists of three parts :-
Ist. A dark central portion, where the issuing gas is un-
mixed with the other, and no combustion takes place ;
2d. The proper burning mixture of the two gases, forming
a shell of some shade of blue, where the greatest beat is
found ; and, 3d. An external shell of a yellowish colour,
generally consisting of the products of combustion. These
are simple flames, and yield light sufficient only to render
themselves visible.

Compound flames are those in which solid particles are
separated during the process, and have the same parts and
structure, with some additions. The most usual exam-
ples of them are hydrocarbons or carburetted hydrogen
gases, such as coal gas. The additional parts are a thin
shell of blue flame at the bottom and coolest part of the
flame, where the gas is not decomposed; while in the
upper part of the flame it suffers decomposition a large
quantity of carbon is separated and raised to a state of
vivid ignition in the form of solid particles, constituting
the white luminous part of the flame.
The mixture of incombustible gases affects the size and
appearance of flames. Hydrogen in coal gas burn with
a larger flame in air than in pure oxygen, because they
require to spread further through air in order to meet with
a sufficient supply of oxygen to combine with. Different
incombustible gases vary in their injurious influence on
flame—the heaviest being the worst, probably from its
light gases spreading through them to a greater extent,
and thus cooling the flame to a greater degree.
Flame was then considered in its practical relations to
heat and light. For the attainment of these results in
their greatest perfection, the principal points to be at-
tended to are, to secure perfect combustion by effecting
mixture of the two gases in their proper combining pro-
portions, to avoid all sources of loss of heat, and for
light, to separate as much as possible of the carbon in the
solid form compatible with perfect and sufficiently intense
combustion. Various modes of effecting these objects
were adverted to.
Smoke is the term given to the products of combustion
of gaseous matter, where they contain visible solid or
liquid particles ; in ordinary cases this consists of carbon,
and is produced by imperfect combustion, gaseous and

solid matter escaping combination with the oxygen of the
air. This may be caused in two ways—first, by the with-
drawal of heat from the flame with such rapidity that it
is cooled, and the combustion checked and rendered im-
perfect, second, by an insufficient supply of the oxygen of
the air either from too limited supply of air, or by the
issue of the gas in so large a volume that the force of
diffusion cannot effect with sufficient rapidity a mixture
with the proper quantity of air for perfect combustion.
The second cause in both its forms is that which produces
smoke in close furnaces in which coal is burnt.
Coal is a compound of carbon and hydrogen, with
smaller proportions of cxygen, nitrogen, and incombus-
tible earthy substances. There are many varieties prin-
cipally interesting, in respect to the proportion of carbon
they contain, some leaving about 96 per cent. of fixed
matter when ignited in close vessels, others only about 44
per cent. For the present purpose it will be most useful
to consider only the truly combustible portion of ordinary
splint or caking coal, as composed of about 100 carbon
and 5% hydrogen, or of 79 carbon and 21 carbonetted
hydrogen.
When coal is heated in close vessels it gives off various
products in thestate of gas or vapour, com posed ofcarbonand
hydrogen in various proportions, but the general result of
which may be taken as equivalent to carbonated hydrogen
gas. These burn in the form or flame, while the remain-
ing carbon burns in the solid form as coke, and 79 parts
of carbon compared with 21 parts of carboneted hydro-
gen require about two and a half times as much oxygen
for perfect combustion. But in considering the subject
economically, if we suppose the whole of the. heat from
the combustion of the gases to be economically applied, it
is necessary to deduct from the combustion of the coke
that proportion which is necessary far the expulsion of the
gaseous matter, and so lost as to its economical applica-
tion. This may be estimated at one-fourth of the coke,
so that while the oxygen consumed by the coke is about
two and a half times as much as that consumed by the
gases and the heat produced proportional, the quantity of
heat available for economical purposes, is somewhat less
than twice as much.
When coal burns the gaseous matter is emitted from
the cracks and crevices which are produced by heat upon
the coal, which produce flames of considerable diameter.
presenting an impediment to the due mixture with a suf-
ficient quantity of air. In a common steam boiler furnace
the quantity of gaseous matter produced on new firing is
very great, while the supply of air is deficient, and its
proper mixture too slow, the consequence is imperfect
combustion and the production of smoke. As the com-
bustion proceeds the quantity of gases evolved diminishes,
and the combustion is more perf•ct. The proper object
should be to make the combustion as perfect as possible
during the whole time.
The object directly looked to is to remove or prevent
black smoke, and for this purpose there are a great num-
ber of plans patented or otherwise. Ist. Washing the
gaseous products of combustion by a shower of water in
flues constructed for the purpose, an effectual method,
but not conveniently applicable in most circumstances,
and not improving the combustion. 2d. Passing the first
products of combustion through or over incandescent coke
already deprived of its gaseous constituents, and effected in
various ways—by simple management in the feeding of
the furnace, by peculiar arrangements, such as two sets of
bars, one fixed and the other moveable, coking boxes, dead
plates or ovens, divided furnace, with alternate feeding,
&c. By such plans, the smoke in passing through the
incandescent coke is deprived of its solid particles of
carbon by their combining with carbonic acid erising from
the burning coke, to form gaseous invisible carbonic oxide,
or should free oxigen be present, the particles of carbon
may be burnt, that is converted into carbonic acid. Upon
the presence and action of oxigen depends entirely the
economical worth of this plan, as the formation of car-
bonic oxide is productive only of loss of heat. 3d. Con-
stant and gradual feeding of the fire by mechanical feeders,
or revolving grates or bars; the worth of this plan is de-
pendant on the perfectness of the combustion, from a suffi-
cient supply and proper mixture of air, as unless this is
the case, the smoke may be rather diffused more uni-
formly over the lime than destroyed ; besides, the machi-
nery is expensive and troublesome, and only adapted for
producing a regular and uniform supply of steam; which
is frequently not all that is desirable. 4th. Admission of
air, besides that by the fire-bars, to burn the gases—the
most correct in theory. Parkes's split bridge is one of
the earliest of such plans, but requires careful manage-
ment, as the admission of such a large body of cold air
is apt to check the combustion of the gases by its cool-
ing effect. To remedy this the air has been heated ; but
when this is effected by the same furnace, it is robbed of
its heat, and the gain consequently more or less neutra-
lised • besides, heated air brings in the same volume a
smaller absolute quantity of ogygen, and moreover, in
some of these plans it is questionable whether the air is
in reality heated to any considerable degree. Another
modification is the admission of the air by numerous
small apertures over a considerable surface, so as to effect
the mixture of the air and gases without cooling them too
much, an arrangement simple, cheap, and of easy manage-
ment. sth. Minor arrangements, such as very narrow
fire-bar=, undulating grates, check bridges—some of these
are useful as subsidiary. 6th. Admission of a jet of
steam : this has been found to do well, but it is accompa-
nied also with the admission of air, and the jet of steam is
supposed merely to increase the draught, otherwise it is not
well understood.

The essential principle is the admission of a sufficient
and not excessive supply of air, and its proper mixture
with the gases, which in practice is somewhat difficult to
effect. It seems very doubtful whether complete com-
bustion can be effected ; probably from the large qnan-
tity of incombustible gases present it is impossible ; the
real object is to effect it as perfectly as possible. When
done on proper principles, the consumption of smoke is
attended with a saving of fuel, as the solid particles in
smoke are just co much carbon loct. Thic is not only a
deduction trom established chemical principles, but the
result of practical observation in the very causes under
consideration.

Mr. Waldie concluded by expressing his opinion of the
necessity for some legislative enactment for the removal
of so grievous a nuisance, and stated his intention of pro-
secuting the subject still further if in his power, with the
view of elucidating more accurately several points con-
nected with the subject.