A great deal has been spoken and written on this subject, but
practically nothing has been _done_. At one time I shared the general
belief in its possibility, and accordingly examined a multitude of
devices for smoke-consuming, and tried several of the most promising,
chiefly in furnaces for metallurgical work, for steam boilers and
stills. None of them proved satisfactory, and I was driven to the
conclusion that smoke-consumption is a delusion, and further, that
_economical_ consumption of smoke is practically impossible. When smoke
is once formed, the cost of burning it far exceeds the value of the
heat that is produced by the combustion of its very flimsy flocculi
of carbon. It is a fiend that once raised cannot be exorcised, a
Frankenstein that haunts its maker, and will not be appeased.
To describe in detail the many ingenious devices that have been
proposed and expensively patented and advertised for this object, would
carry me far beyond the intended limits of this paper. I must not even
attempt this for a selected few, as even among them there is none that
can be pronounced satisfactory.
The common idea is that if the smoke be carried back to the fire
that produced it, and made to pass through it again, a recombustion
or consumption of the smoke will take place. This is a mistake, as a
little reflection will show. First, let us ask why did this particular
fire produce such smoke? Everybody now-a-days can answer this question,
as we all know that smoke is a result of imperfect combustion, and,
knowing this, it can easily be understood that to return the carbonic
acid and excess of carbon to the already suffocated fire can only add
smother to smotheration, and make the smoky fire more smoky still.
There is, however, one case in which a fire _appears_ to thus consume
its own smoke, but the appearance is delusive. I refer to fires lighted
from above. These, if properly managed, are practically smokeless,
and it is commonly supposed that smoke passes from the raw coal below
through the burning coal above, and is thereby consumed. The fact
is, however, that no such smoke is formed. That which under these
conditions comes from the coal beneath, when gradually heated by the
fire above, is combustible _gas_, and this gas is burned as it passes
through the fire. In this case the formation or non-formation of
smoke depends mainly on how this gas is burned, whether completely or
incompletely. If the air supplied for its combustion is insufficient,
smoke will be formed as it is when we turn up an Argand gas-flame so
high that the gas is too great in proportion to the quantity of air
that can enter the glass chimney.
Herein lies the fundamental principle. We may _prevent_ smoke, though
we cannot _cure_ it, and this prevention depends upon how we supply
air to the gas which the coal gives off when heated, and upon the
condition of this gas when we bring it in contact with the air by which
its combustion is to be effected. We must always remember that coal
when its temperature is sufficiently heated, whether in a gas retort
or fireplace, gives off a series of combustible hydrocarbon gases and
vapors, and all we have to do in order to obtain smokeless fires is to
secure the complete combustion of these.
Now we know that to burn a given quantity of gas we must supply it
with a sufficient quantity of oxygen, _i.e._, of the active principle
of the air; but this is not all: we all know well enough that if cold
coal-gas and cold air be brought together in any proportion whatever
no combustion occurs. A certain amount of heat is necessary to start
the chemical combination of oxygen with hydrogen and carbon, which
combination is the combustion, or burning.
Therefore, when the coal gas and the air are brought together one or
the other, or both, must be heated up to a certain point in order
that the combustion be complete. If cold there is no combustion; if
insufficiently heated, there is imperfect combustion, however well the
supplies may be regulated.
A very simple experiment that anybody may make illustrates this. When
an ordinary open fire is burning brightly and clearly without flame,
throw a few small pieces of raw coal into the midst of the glowing
coals. They will flame fiercely, but without smoking. Then throw a heap
of coal or one large lump on a similar fire. Now you will have dense
volumes of smoke, and little or no flame, simply because the cooling
action of the large bulk of coal in the course of distillation brings
the temperature of its gases below that required for their complete
combustion.
This simple experiment supplies a most important practical lesson,
as well as a philosophical example. The best of all smoke-abatement
machines is an intelligent and conscientious stoker, and every
contrivance for smoke abatement must, in order to be efficient, either
be fed by such a stoker or provided with some automatic arrangement by
which the apparatus itself does the work of such a stoker by supplying
the fresh fuel just when and where it is wanted.
Cornish experience is very instructive in this respect. The engines
that pump the water from the mines do a definitely measurable amount of
work, and are made to register this. The stoker is a skilled workman,
and prizes are given to those who obtain the largest amount of “duty”
from given engines per ton of coal consumed. Instead of pitching his
coal in anyhow, cramming his fire-hole, and then sitting down to sleep
or smoke in company with his chimney, the Cornish, or other good
fireman, feeds little and often, and deftly sprinkles the contents of
his shovel just where the fire is the brightest and the hottest, and
the bars are the least thickly covered. The result is remarkable. A
colliery proprietor of South Staffordshire was visiting Cornwall, and
went with a friend to see his works. On approaching the engine-house
and seeing a whitewashed shaft with no smoke issuing from its mouth,
he expressed his disappointment at finding that the engine was not at
work. To all who have been accustomed to the “Black Country,” where
coal is so shamefully wasted because it is cheap, the tall clean
whitewashed shafts of Cornwall, all so smokeless, present quite an
astonishing appearance.
This is not a result of “smoke-consuming” apparatus, but mainly of
careful firing. It was in the first place promoted by the high price
of coal due to the cost of carriage before the Cornish railways were
constructed, and it brought about a curious result. Horse-power for
horse-power the cost of fuel for working Cornish pumping engines has
been brought below that of pumping engines in the places where the
price of coal per ton was less than one-half. Another coal famine that
should raise the price of coal in London to 60_s._ per ton, and keep it
there for two or three years, would effect more smoke abatement than we
can hope to result from the present and many future South Kensington
efforts. I need scarcely dwell upon the necessity for a due supply of
air. This is well understood by everybody. An over supply of air does
mischief, by carrying away wastefully a proportionate quantity of heat.
The waste due to this is sometimes very serious.
After reviewing all that has been done, the conclusion that London
cannot become a clean, smokeless, and beautiful city, so long as we are
dependent upon open fire-grates of anything like ordinary construction,
and fed with bituminous coal, is inevitable. The general use of
anthracite would effect the desired change, but there is no hope of its
becoming general without legislative compulsion, and Englishmen will
not submit to this.
One of the most hopeful schemes is that which was propounded a short
time since by Mr. Scott Moncrieff. Instead of receiving our coal in
its crude state he proposes that we should have its smoke-producing
constituents removed before it is delivered to us; that it should
be made into a sort of artificial semi-anthracite at the gas-works
by a process of half distillation, which would take away not _all_
the flaming gas as at present, but that portion which is by far the
richest to the gas-maker and the most unmanageable in common fires.
We should thus have a material which, instead of being so difficult to
light as coke and anthracite, would light more easily than crude coal,
and at the same time our gas would have far greater illuminating power,
as it would all be drawn off during the early period of distillation,
when it is at its richest. From a given quality of coal the difference
would be as twenty-four candles to sixteen. The ammonia which we now
throw into the air, the naphtha and coal-tar products, which we waste,
are so valuable that they would pay all the expenses at the gas-works
and leave a handsome profit. We should thus get gas so much better that
two burners would do the work now obtained from three. We should get
all we require for lighting purposes and plenty more for heating; the
intermediate profits of the coal merchant would be abolished, and our
solid fuel of far better quality could be supplied twenty or thirty per
cent cheaper than at present, provided always that the gas monopoly
were abolished, “a consummation most devoutly to be wished for.”
Mr. Moncrieff (who brought forward his scheme without any
company-mongering, or claims for patent rights) estimates the saving to
London at £2,125,000 per annum, over and above the far greater saving
that would result from the abolition of smoke.
In connection with this scheme I may mention a fact that has not been
hitherto noted, viz., that we have perforce and unconsciously done a
little in this direction already. Formerly London was supplied almost
exclusively with “Wallsend” and other sea-borne coals of a highly
bituminous composition—soft coals that fused in the grate and caked
together. Partly owing to exhaustion of the seams, and partly to the
competition of railway transit, we now obtain a large proportion of
hard coal from the Midlands. This is less smoky and less sooty, and
hence the Metropolitan smoke nuisance has not increased quite as
greatly as the population.
But I will now conclude by repeating that whatever scheme be chosen,
“smoke abatement” is to be achieved, _not by smoke-consumption, but by
smoke-prevention_.