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.
The Earl of Dundonald has shown that, in the application for burning lime, a quantity of coke uniformly burns a given portion of lime-stone in one-third part of the time that the quantity of coal from which the coke had been made could do.
This effect is to be accounted for from having previously freed the coal, or rather its coke, from the moisture and the tar, which it sends out during combustion, and which condenses on the middle and upper strata of stratified limestone and coal in the lime kiln, and impedes the whole mass of materials from coming into a rapid and compleat ignition; because the greater the quantity of materials, and the sooner the whole is ignited, the better and more economically the lime is burned, both as to coals and time; the saving of which last is a material object, especially at lime-kilns where there is in the summer time a great demand for lime, the coke occasioning the kilns to hold a _third more lime_ at the _same time_.
In the art of making bricks, in the smelting of metallic ores, and the drying of malt, the advantages of coke over coal, are sufficiently known.
The following account given by Mr. Davis,[29] shows that the advantages that may be derived in the processes of burning lime, plaster of paris, and bricks, by means of coke, are greater than at first sight might be imagined.
[29] Philosophical Magazine, Vol. 33, p. 435.
“The coke obtained in the gas process is so valuable, that it appears inexplicable that men should not avail themselves of this mode of procuring light, to the almost total exclusion of all other methods now in use. As a landholder, placed among an industrious but wholly illiterate society of men, I have had the more opportunity of trying this species of fuel or coke, which I could not otherwise procure in this sequestered spot, at a tolerably cheap rate, for purposes to which it has not, as far as I know, been hitherto employed. I must tell you that I am my own lime-burner, plaster of paris baker, and brick-maker; and that in these processes of rural economy I have derived the greatest benefits from this species of fuel, which I now prepare at a cheap rate, although I waste almost the whole of the light of the coal gas intentionally. The coal which I employed formerly for the burning of limestone into lime, is a very inferior kind of small coal, called here Welsh culm. The kiln for burning the limestone into lime is a cup-shaped concavity, surrounded with solid brick-work, open at the top, and terminating below by an iron grate. It has a stone door that may be opened and closed for charging and emptying the furnace when required. This furnace I formerly charged with alternate strata or layers of small coal and limestone, the latter being broken previously into pieces not larger than a man’s fist, until the kiln was completely filled. The stone is thus slowly decomposed; the upper part of the charge descends, and when it has arrived at the bottom of the furnace new strata are super-imposed, so as to keep the furnace continually full during a period of 50 hours. The quantity of lime I procured with small coal formerly amounted to 85 bushels. The strata of coal necessary for the production of this quantity of lime require to be four inches thick, and the time necessary for calcination was, as stated already, 50 hours.