In the metropolis the Newcastle coal is chiefly used, and this, we perceive, yields five per cent. ashes and about 57 per cent. carbon. But a considerable part of the carbon is converted into carbonic acid during combustion; if, therefore, we assume that two-thirds of the carbon are thus consumed, and that the remaining third remains behind in the form of cinder, we shall have about 25 per cent. of “dust” from every ton of coal. On inquiry of those who have had long experience in this matter, I find that a ton of coal may be fairly said on an average to yield about one-fourth its weight in dust; hence the gross amount of “dust” annually produced in London would be 900,000 tons, or about three tons per house per annum.
It is impossible to obtain any definite statistics on this part of the subject. Not one in every ten of the contractors keeps any account of the amount that comes into the “yard.” An intelligent and communicative gentleman whom I consulted on this matter, could give me no information on this subject that was in any way satisfactory. I have, however, endeavoured to check the preceding estimate in the following manner. There are in London upwards of 300,000 inhabited houses, and each house furnishes a certain quota of dust to the general stock. I have ascertained that an average-sized house will produce, in the course of a year, about three cart-loads of dust, while each cart holds about 40 bushels (baskets)—what the dustmen call a chaldron. There are, of course, many houses in the metropolis which furnish three and four times this amount of dust, but against these may be placed the vast preponderance of small and poor houses in London and the suburbs, where there is not one quarter of the quantity produced, owing to the small amount of fuel consumed. Estimating, then, the average annual quantity of dust from each house at three loads, or chaldrons, and the houses at 300,000, it follows that the gross quantity collected throughout the metropolis will be about 900,000 chaldrons per annum.
The next part of the subject is—what becomes of this vast quantity of dust—to what use it is applied.
The dust thus collected is used for two purposes, (1) as a manure for land of a peculiar quality; and (2) for making bricks. The fine portion of the house-dust called “soil,” and separated from the “brieze,” or coarser portion, by sifting, is found to be peculiarly fitted for what is called breaking up a marshy heathy soil at its first cultivation, owing not only to the dry nature of the dust, but to its possessing in an eminent degree a highly separating quality, almost, if not quite, equal to sand. In former years the demand for this finer dust was very great, and barges were continually in the river waiting their turn to be loaded with it for some distant part of the country. At that time the contractors were unable to supply the demand, and easily got 1l. per chaldron for as much as they could furnish, and then, as I have stated, many ships were in the habit of bringing cargoes of it from the North, and of realizing a good profit on the transaction. Of late years, however—and particularly, I am told, since the repeal of the corn-laws—this branch of the business has dwindled to nothing. The contractors say that the farmers do not cultivate their land now as they used; it will not pay them, and instead, therefore, of bringing fresh land into tillage, and especially such as requires this sort of manure, they are laying down that which they previously had in cultivation, and turning it into pasture grounds. It is principally on this account, say the contractors, that we cannot sell the dust we collect so well or so readily as formerly. There are, however, some cargoes of the dust still taken, particularly to the lowlands in the neighbourhood of Barking, and such other places in the vicinity of the metropolis as are enabled to realize a greater profit, by growing for the London markets. Nevertheless, the contractors are obliged now to dispose of the dust at 2s. 6d. per chaldron, and sometimes less.
The finer dust is also used to mix with the clay for making bricks, and barge-loads are continually shipped off for this purpose. The fine ashes are added to the clay in the proportion of one-fifth ashes to four-fifths clay, or 60 chaldrons to 240 cubic yards, which is sufficient to make 100,000 bricks (where much sand is mixed with the clay a smaller proportion of ashes may be used). This quantity requires also the addition of about 15 chaldrons, or, if mild, of about 12 chaldrons of “brieze,” to aid the burning. The ashes are made to mix with the clay by collecting it into a sort of reservoir fitted up for the purpose; water in great quantities is let in upon it, and it is then stirred till it resembles a fine thin paste, in which state the dust easily mingles with every part of it. In this condition it is left till the water either soaks into the earth, or goes off by evaporation, when the bricks are moulded in the usual manner, the dust forming a component part of them.
The ashes, or cindered matter, which are thus dispersed throughout the substance of the clay, become, in the process of burning, gradually ignited and consumed. But the “brieze” (from the French briser, to break or crush), that is to say, the coarser portion of the coal-ash, is likewise used in the burning of the bricks. The small spaces left among the lowest courses of the bricks in the kiln, or “clamp,” are filled with “brieze,” and a thick layer of the same material is spread on the top of the kilns, when full. Frequently the “brieze” is mixed with small coals, and after having been burnt the ashes are collected, and then mixed with the clay to form new bricks. The highest price at present given for “brieze” is 3s. per ton.
The price of the dust used by the brickmakers has likewise been reduced; this the contractors account for by saying that there are fewer brick-fields than formerly near London, as they have been nearly all built over. They assert, that while the amount of dust and cinders has increased proportionately to the increase of the houses, the demand for the article has decreased in a like ratio; and that, moreover, the greater portion of the bricks now used in London for the new buildings come from other quarters. Such dust, however, as the contractors sell to the brick-makers, they in general undertake, for a certain sum, to cart to the brick-fields, though it often happens that the brick-makers’ carts coming into town with their loads of bricks to new buildings, call on their return at the dust-yards, and carry thence a load of dust or cinders back, and so save the price of cartage.
But during the operation of sifting the dust, many things are found which are useless for either manure or brick-making, such as oyster shells, old bricks, old boots and shoes, old tin kettles, old rags and bones, &c. These are used for various purposes.
The bricks, &c., are sold for sinking beneath foundations, where a thick layer of concrete is spread over them. Many old bricks, too, are used in making new roads, especially where the land is low and marshy. The old tin goes to form the japanned fastenings for the corners of trunks, as well as to other persons, who re-manufacture it into a variety of articles. The old shoes are sold to the London shoemakers, who use them as stuffing between the in-sole and the outer one; but by far the greater quantity is sold to the manufacturers of Prussian blue, that substance being formed out of refuse animal matter. The rags and bones are of course disposed of at the usual places—the marine-store shops.
A dust-heap, therefore, may be briefly said to be composed of the following things, which are severally applied to the following uses:—