A Practical Treatise on Gas-light / Exhibiting a Summary Description of the Apparatus and Machinery Best Calculated for Illuminating Streets, Houses, and Manufactories, with Carburetted Hydrogen, or Coal-Gas, with Remarks on the Utility, Safety, and General Nature of this new Branch of Civil Economy.

by Friedrich Christian Accum

It is sufficiently known, that coke is a more valuable fuel than the coal from which it is obtained.

Hence, immense quantities are prepared in the large way, but the gazeous and other substances are lost in the process employed for carbonizing the coal.[27] In the manufacture of coal-gas, the coke comes from the retort, enlarged in size, and greatly diminished in weight, when compared with the original coal. In whatever state the coal may be when introduced into the retort, the coke is uniformly taken out in large masses, so that the refuse coal, or dust, and sweepings of the pit, which are now thrown away, may be employed and converted into an excellent fuel. Coke is decidedly superior to coal for all domestic, and more especially for culinary purposes; the heat which it throws out being more uniform, more intense, and more durable. No flame, indeed, accompanies it, and it seldom needs the application of the poker,—that specific for the ennui of Englishmen; but these deficiences are more than balanced by the valuable property of emitting no sparks, of giving more heat, and burning free from dust and smoke.

[27] The preparation of coke is as follows:—A quantity of large coal is placed on the ground in a round heap, of from 12 to 15 feet in diameter, and about two feet in height; as many as possible of the large pieces are placed on their ends, to form passages for the air; above them are thrown the smaller pieces and coal dust, and in the midst of this circular heap, is left, a vacancy of a foot wide where a few faggots are deposited to kindle it. Four or five apertures of this kind are formed round the ring, particularly on the side exposed to the wind; there is, however, seldom occasion to light it with wood, for other masses being generally on fire, the workmen most frequently use a few shovels of coal already burning, which acts more rapidly than wood, and soon kindles the surrounding pile; as the fire spreads, the mass increases in bulk, puffs up, becomes spongy and light, cakes into one body, and at length loses its volatile parts, and emits no more smoke. It then acquires an uniform red colour, inclining a little to white, in which state it begins to break into gaps and chinks, and assumes the appearance of the under part of a mushroom; at this moment the heap must be quickly covered with ashes, of which there is always a sufficient provision around the numerous fires, where the coke is prepared.

That coke must give out more heat during its combustion than coal, will at once become obvious, when we consider that the quantity of matter which, in the combustion of coal is changed from a solid to a state of elastic fluidity, must necessarily carry off a portion of caloric, which then becomes converted in a latent state without producing heat, whilst the glow of the coke radiates caloric with an intensity unimpaired by any demand of this kind.

It is thus that coke, though somewhat more difficult of ignition than common coal, always gives out a more steady, a more lasting, and a more intense heat.

The only inconveniences that attend the use of coke is, that, as it consumes, it leaves much more ashes than common coal, charcoal, or wood; and these much heavier too, which are, therefore, liable to collect in such quantity as to obstruct the free passage of air through the fire; and further, that when the heat is very intense, these ashes are disposed to melt or vitrify into a tenacious drossy substance, which clogs the grate, the sides of the furnace and the vessels. This last inconvenience is only troublesome, however, when the heat required is very great. In ordinary heats, such as are produced by kitchen or parlour grates, the ashes do not melt, and though they are more copious and heavy than those of charcoal or wood, they do not choke up the fire, unless the bars of the grate be too close together.

The relative effects of heat produced by coke and coal are as follows:—

Six hundred pounds of pit-coal are capable of evaporating 10 cubic feet of water in 20 hours, and 430lb. of coke are capable of evaporating 17 cubic feet of water in 12 hours and a half.[28]

[28] In order to learn the relative effect of different kinds of fuel, with regard to their capability of producing heat, chemistry teaches that equal quantities of fuel alike expended, will raise the temperature of a given quantity of water through the same number of degrees; whence, by knowing the original quantity and temperature of water, together with the quantity of fuel expended to raise the water to the boiling point, the result sought may be expressed by stating the quantity of water at 30 degrees, which would have been raised 180 degrees by one pound of the fuel employed; or in the form of a rule,

Multiply the quantity of water by the number expressing the degrees actually raised; multiply the number of pounds of fuel expended by 180 degrees. Divide the first product by the latter, and the quotient will express the water which would have been raised 180 degrees by one pound of the fuel. Or equal quantities of water may be compleatly evaporated under equal surfaces and circumstances, with the different kinds of fuel, the nature of which is to be examined; the quantities of fuel expended for that purpose give the relative effect of the different kinds of fuel, with regard to their power of producing heat.