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Keeping these objects in view, the heads of enquiry will be, in this and the next Lecture,—

I. The elementary constituents of coal and other fuels. II. The relative proportions of the furnace, and forms of boilers.

III. The temperature of the furnace and surrounding flues.

IV. The economy of fuel, concentration of heat, and prevention of smoke.

Lastly, General summary of results.

I. The constituents of coal and other fuels.

The first practical enquiries into the nature and constituents of coal are probably those of Dr. Thomson and Mr. Mushet; several others have investigated their chemical composition, but the discrepancies which exist in the varied forms of analysis render them of little value when applied to the useful arts. Dr. Thomson examined four distinct species of coal, of which the following are the results

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Dr. Ure also supplies an analysis of splint and cannel coal, which differ from those experimented upon by Dr. Thomson, as follows:

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The chief difference between the experiments seems to consist in the increased quantity of hydrogen in Dr. Thomson's cannel coal, and the total absence of oxygen, which in Dr. Ure's specimens was found in excess.

The next authority is Mr. Mushet, who analysed nearly the whole of the Welsh coals, and some others, of which the following are selected, viz.—

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Again, we have some of the American anthracites, with upwards of 90 per cent. of carbon and 3.6 of volatile matter, which correspond with nearly all the other descriptions of anthracites as given by Mr. Mushet, and more recently by Dr. Kane, in his excellent work' On the Industrial Resources of Ireland.'

In addition to the above, Dr. Fife has given some valuable experiments on coal, wherein he does not materially differ in the bituminous qualities from those of Mr. Mushet. The results of Dr. Fife's experiments were found to be in the bituminous and anthracite kinds :

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It will be observed from these experiments that considerable differences exist as to the quantity of carbon contained in each sort; and provided it be correct that the heating power of any description of fuel is in proportion to the quantity of carbon it contains, it then follows that the anthracite must be greatly superior to the bituminous qualities, which yield little more than onehalf the quantity of carbon. Considerable difficulty is, however, encountered in the combustion of the anthracite coal, as intense heat is not only an element, but time, and a large quantity of oxygen, are absolutely necessary to volatilise its products. It has been known to pass twice through an iron smelting furnace, and subjected for upwards of forty hours to the temperature of melting iron, without being affected beyond the exterior surface, having been calcined to a depth of not more than threefourths of an inch. Such, however, is the obduracy of its character, that intense heat makes little or no im

pression upon it. To burn anthracite coal effectually,

and to extract the whole of its volatile products, it must be broken into small pieces, and thrown upon a furnace having a large supply of oxygen passing continually through it.

In the combustion of bituminous coal the operation is totally different, being partly friable, and splitting into fragments as the gases are evolved; and hence arises the superior value of this description of fuel in almost every branch of the industrial arts.

The Newcastle and the best qualities of the Durham coal are exceptions to most others of the bituminous kind; they contain a much greater quantity of carbon, and are thus better fitted for the furnace. From some accurate experiments by Mr. Richardson they are found to contain

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The Lancashire coals approach nearer to the Newcastle and Durham than most others; and, taking the mean of some recent experiments, they contain

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The specific gravity of the Lancashire coal is rather more than that of the Newcastle coal; but in other respects their constituents are much alike, with the exception of a greater proportion of ashes in the former than is found in the finer qualities of the latter.

Dr. Kane, in his recent work On the Industrial Resources of Ireland' (already alluded to), has given some valuable information on the properties of the Irish anthracites and other coals found in different districts of the country. He also ascertained the value of the different beds of lignite, which retained their original woody structure and burned with a brilliant light, leaving a residuum of black dense charcoal.

The constituents of two specimens analysed by Dr. Kane gave

Volatile matter

Pure charcoal

Ashes

(1.)

(2.)

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From the above it would appear that the economic

value of lignite is about two-thirds of an average quality of good coal; and comparing these with other results obtained from similar. lignites, two-thirds may fairly be taken as the calorific value of this description of fuel. Dr. Kane further examined a great variety of turf, and amongst others those prepared by Mr. C. W. Williams from the bogs of Cappage, Kilbeggan, Kilbaken, &c.; the elementary products of which are, according to Dr. Kane, as follows:

Carbon

Hydrogen

Oxygen

Ashes

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It will be unnecessary to exemplify a greater variety of fuels, such as the different kinds of wood used in America, Russia, and different parts of the Continent. In this country timber is seldom, if ever, used; and taking the comparative merits of the fuels already enumerated, it will be found (in assuming the quantity of carbon contained in each as the measure of their respective values) that the Welsh furnace coal and the Newcastle and Lancashire coals stand preeminent in the order of their heating powers, both as regards their application to the furnace, and to the ordinary purposes of domestic life.

The American anthracites, which in some cases contain upwards of 90 per cent. of carbon, are extensively used in that country; and assuming the mean, 91·4, of Professor Johnston's experiments to be correct, and calling it 1,000, we then have an approximate value of the different fuels experimented upon and in general use in this country.

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