the amount of this loss in coal by rotating in a barrel different qualities of coal for the same time. The powder produced was separated and weighed, and in this way the friability or cohesion of a fuel could be expressed in percentages. Schrötter made the same experiments with

brown coal.

The size and form of the pieces composing the fuel is important, as on this depends the space occupied in its stowage an important point for steam-vessels. This space cannot be calculated from its specific gravity, but must be ascertained by direct measurement. The space occupied will be smallest when the form of the lumps is cubical. Playfair and De la Beche have also investigated this subject.

2. DETERMINATION OF THE ADHERING WATER.-The water contained in a fuel exerts great influence on its heating power. It not only increases its bulk, but it acts injuriously by abstracting a certain quantity of heat required for its evaporation, and it also causes imperfect combustion. For this reason, wood, turf, and brown coal never give so high a temperature as coal, anthracite, and coke.

The determination of the adhering water is effected by drying a certain weight of the pounded fuel in a water-bath at 212° F. or in an air-bath at 220°. It may also be ascertained by placing a certain weight of the powdered fuel in a glass tube, heating to 212°, and passing over it air dried by means of chloride of calcium, till the fuel no longer loses weight. The amount of water which the dried fuel will absorb from the atmosphere in twenty-four hours, should also be determined, in order to ascertain its hygroscopic qualities.

3. DETERMINATION OF THE SPECIFIC GRAVITY.-The specific gravity of a fuel depends on its density and the amount of ash, and it appears also to be in proportion to its greater or less inflammability. Of two equal volumes of carbonised fuel, the one will produce the greatest heating effect which has the greatest specific gravity, provided the density is not produced by mineral constituents.

Wien, akad. Ber. 1849, Nov. and Dec. p. 240. Liebig's 'Jahresber.,' 1849, p. 709.

The determination of the specific gravity is difficult, and sometimes uncertain, owing to the cleavage of the fuel, and the entanglement of air in its pores. The best way of obviating this difficulty, is to finely powder the fuel before taking its specific gravity. Full directions will be found in a subsequent chapter.

4. DETERMINATION OF THE ABSOLUTE HEATING POWER.The value of a fuel for any purpose depends chiefly on its price and the quantity required for that purpose. The quantity required depends on the heating power possessed by a certain weight of fuel (its absolute heating power) or that possessed by a certain volume (its specific heating power).

The less oxygen, ash, and water the fuel contains, the greater its heating power will be, and this will also increase in proportion to the carbon and hydrogen present.

Whether the combustion is effected quickly or slowly, the amount of heat produced will be the same, but the degree of temperature attained will be very different. This latter constitutes the pyrometric heating power.

The determination of the absolute heating power of a fuel may be effected,

a. By heating a definite quantity of water from 32° F. to 212°;

b. By ascertaining how much fuel is required to melt a known weight of ice;

c. By ascertaining how much water may be evaporated by 1 lb. of different kinds of fuel ;

d. By ascertaining how much the temperature of a room increases by burning a certain weight of a fuel in a stove.

e. By ascertaining the elementary composition of the fuel, and calculating how much oxygen will be required to convert the carbon and hydrogen into carbonic acid and water; the quantity of heat produced will be in proportion to the amount of oxygen consumed.

f. By Berthier's method,

9. By Dr. Ure's method.

According to Berthier, the most convenient method

for ascertaining the comparative calorific power of any combustible matter is by means of litharge. He says: It has been proved by the experiments of many philosophers, that the quantities of heat emitted by combustible substances are exactly proportioned to the amounts of oxygen required for their complete combustion. Whence, after the elementary constitution of any combustible is known, its calorific power is easily determined by calculation. For instance, it is only necessary to ascertain the quantity of oxygen absorbed in the conversion of all its carbon into carbonic acid, and all its hydrogen into water, and compare that quantity with that which is consumed in burning a fuel whose calorific power is well ascertained. Such a substance is charcoal.

By adopting the principle just pointed out, it may be conceived that, without knowing the composition of a fuel, its heating power may be ascertained by determining the amount of oxygen it absorbs in burning. This can be done in a very simple and expeditious manner, if not exactly, at least with sufficient exactitude to afford very useful results in practice. It is as follows: many metallic oxides are reduced with such facility that when heated with a combustible body, the latter burns completely, without any of its elements escaping the action of the oxygen of the oxide, if the operation be suitably performed. The composition of the oxide being well known, if the weight of the part reduced to the metallic state be taken, the quantity of oxygen employed in the combustion can be ascertained. In order to collect the metal and separate it from the non-reduced mass, it must be fusible as well as its oxide. Litharge fulfils these conditions, and experiment has proved that it completely burns the greater part of all ordinary fuels; the only exceptions are some very bituminous matters containing a large proportion of volatile elements, a portion of which escapes before the temperature is sufficiently high to allow the reduction to take place. The experiment is made as follows:-10 grains of the finely-powdered, or otherwise divided fuel is mixed with about 400 grains of litharge. The mixture is carefully placed in an earthen crucible, and

covered with 200 grains more litharge. The crucible is then placed in the fire and gradually heated. When the fusion is perfect, the heat is urged for about ten minutes, in order that all the lead may collect into a single button. The crucible is then taken from the fire, cooled, broken, and the button of lead weighed. Sometimes the button is livid, leafy, and only slightly ductile; in which case it has absorbed a little litharge. This can be partially prevented by fusing slowly, and adding a little borax.

Two assays, at least, ought to be made, and those results which differ more than a grain or two ought not to be relied on. The purer the litharge, the better the result; it ought to contain as little minium as possible. It is an excellent plan to mix up the litharge of commerce with one or two thousandths of its weight of charcoal, and fuse the whole in a pot; when cold, pulverise the litharge, which will now be deprived of minium.

Pure carbon produces, with pure litharge, thirty-four times its weight of lead, and hydrogen 1037 times its weight of lead; that is to say, a little more than three times as much as carbon. We can, therefore, from these any fuel, either in carbon or

data, find the equivalent of hydrogen.

When a fuel contains volatile matters, the quantity can be ascertained, as before pointed out, by ignition in a close tube or crucible. If, further, we ascertain the proportion of lead it gives with litharge, it is easy to calculate the equivalent in carbon of the volatile matters, and, in consequence, to ascertain its calorific value.

Supposing that a substance gives by distillation C parts of coke, or carbon, having deducted the weight of the ash and of volatile substances, and that it produces P parts of lead with litharge. The quantity C of carbon would give 34 × C of lead; the quantity of volatile matter would give but P 34 x C; it would be equivalent to of carbon: whence it follows that the quantity of heat developed by the charcoal, the volatile matter, and the unaltered combustible, will be to each other as the numbers 34 × C, P 34 x C, and P.

P 34 x C

34

Dr. Ure* says, speaking of the above method of assay, 'On subjecting this theory to the touchstone of experiment, I have found it to be entirely fallacious. Having mixed very intimately 10 grains of recently calcined charcoal with 1000 parts of litharge, both in fine powder, I placed the mixture in a crucible, which was so carefully covered as to be protected from all fuliginous fumes, and exposed it to distinct ignition.

No less than 603 grains of lead were obtained, whereas, by Berthier's rule, only 340 or 346-6 were possible. On igniting a mixture of 10 grains of pulverised anthracite with 500 grains of pure litharge previously fused and pulverised, I obtained 380 grains of metallic lead. In a second experiment, with the same anthracite and the same litharge, I obtained 450 grains of lead; and in a third, only 350 grains. It is therefore obvious that this method of Berthier's is altogether nugatory for ascertaining the quantity of carbon in coals, and is worse than useless in judging of the calorific qualities of different kinds of fuel.'

This discrepancy in the results obtained by Dr. Ure is very perplexing, and does not at all accord with Berthier's experience, as shown by his experiments, or by the author's, on the subject. The latter never had a difference of more than 50 grains, and in general only two or three, which latter result is satisfactory. The only precaution he found necessary was to heat very gradually until the mixture was fully fused, and then to increase the fire to bright redness for a few minutes.

Further experiments have been made by the author on this subject, and he has succeeded most perfectly in estimating the value of a fuel. With the litharge of commerce, which contains much minium, the process is never exact: results have been obtained differing as much as 40 or 50 grains when the litharge employed had not been purified, and to purify it completely is a troublesome process. This difficulty may be completely obviated, however, by substituting for litharge, white lead, using for each 10 grains of 'Supplement to the Dictionary of Arts, Mines, and Manufactures.'