whatever is proper to burn, or make a fire, either for warming a room or dressing victuals. The fuel most generally used in Great Britain is pit coal, which is a very expensive article; and that expense is greatly increased by the waste of coal occasioned by the injudicious manner in which fires in open chimneys are commonly managed. The enormous waste of fuel in London, for instance, may be estimated by the vast dark cloud which continually hangs over that great metropolis, and frequently overshadows the whole country far and wide; for this dense cloud is certainly composed almost entirely of unconsumed coal, which has escaped by the chimneys, and continues to fail about in the air, till, having lost the heat which gave it volatility, it falls in a dry shower of extremely fine black dust to the ground, obscuring the atmosphere in its descent, and frequently changing the brightest day into more than Egyptian darkness.
"I never (says Count Rumford) view from a distance, as I come into town, this black cloud which hangs over London, without wishing to be able to compute the immense number of chaldrons of coals of which it is composed; for could this be ascertained, I am persuaded striking a fact would awaken the curiosity, and excite the astonishment of all ranks of the inhabitants; and perhaps turn their minds to an object of economy to which they have hitherto paid little attention."
The object to which the benevolent author more particularly wishes to direct the public attention, is the lighting of a coal fire, in which more wood should be employed than is commonly used, and fewer coals; and as soon as the fire burns bright, and the coals are well lighted, and not before, more coals should be added to increase the fire to its proper size.
Kindling balls, composed of equal parts of coal,—charcoal,—and clay, the two former reduced to a fine powder, powder, well mixed and kneaded together, with the clay moistened with water, and then formed into balls of the size of hens eggs, and thoroughly dried, might be used with great advantage instead of wood for kindling fires. These kindling balls may be made so inflammable as to take fire in an instant and with the smallest spark, by dipping them in a strong solution of nitre and then drying them again; and they would neither be expensive nor liable to be spoiled by long keeping. Perhaps a quantity of pure charcoal, reduced to a very fine powder, and mixed with the solution of nitre in which they are dipped, would render them still more inflammable.
The Count thinks that the fires which are made in the open chimneys of elegant apartments might be greatly improved by preparing the fuel; for nothing (says he) was ever more dirty, inelegant, and disagreeing than a common coal fire.
Fire balls, of the size of goose eggs, composed of coal and charcoal in powder, mixed up with a due proportion of wet clay, and well dried, would make a much more cleanly, and in all respects a pleasanter fire than can be made with crude coals; and, he believes, would not be more expensive fuel. In Flanders, and in several parts of Germany, and particularly in the duchies of Juliers and Bergen, where coals are used as fuel, the coals are always prepared before they are used, by pounding them to a powder, and mixing them up with an equal weight of clay, and a sufficient quantity of water to form the whole into a mass, which is kneaded together and formed into cakes; which cakes are afterwards well dried and kept in a dry place for use. And it has been found, by long experience, that the expense attending this preparation is amply repaid by the improvement of the fuel. The coals, thus mixed with clay, not only burn longer, but give much more heat than when they are burnt in their crude state.
It will doubtless appear extraordinary to those who have not considered the subject with some attention, that the quantity of heat produced in the combustion of any given quantity of coals should be increased by mixing the coals with clay, which is certainly an incombustible body; but the phenomenon may be explained in a satisfactory manner.
The heat generated in the combustion of any small particle of coal existing under two distinct forms, namely, in that which is combined with the flame and smoke which rise from the fire, and which, if means are not found to stop it, goes off immediately by the chimney and is lost,—and the radiant heat which is sent off from the fire in all directions in right lines.—It is therefore reasonable to conclude, that the particles of clay, which are surrounded on all sides by the flame, arrest a part at least of the combined heat, and prevent its escape; and this combined heat, so arrested, heating the clay red hot, is retained in it; and being changed by this operation to radiant heat, is afterwards emitted, and may be directed and employed to useful purposes. In the composition of fire balls, the Count thinks it probable that a certain proportion of chaff, of straw cut very fine, or even of saw-dust, might be employed with great advantage.