HEATING POWER OF DIFFERENT KINDS OF FUEL.
| Air-dry Wood | 2800 | |
| Air-dry Peat | 2500 | 3000 |
| Perfectly dry Wood | 3600 | |
| Perfectly dry Peat | 3000 | 4000 |
| Air-dry Lignite or Brown Coal | 3300 | 4200 |
| Perfectly dry Lignite or Brown Coal | 4000 | 5000 |
| Bituminous Coal | 3800 | 7000 |
| Anthracite | 7500 | |
| Wood Charcoal | 6300 | 7500 |
| Coke | 6500 | 7600 |
4.—Modes of Burning Peat.
In the employment of peat fuel, regard must be had to its shape and bulk. Commonly, peat is cut or moulded into blocks or sods like bricks, which have a length of 8 to 18 inches; a breadth of 4 to 6 inches, and a thickness of 1-½ to 3 inches. Machine peat is sometimes formed into circular disks of 2 to 3 inches diameter, and 1 to 2 inches thickness and thereabouts. It is made also in the shape of balls of 2 to 3 inches diameter. Another form is that of thick-walled pipes, 2 to 3 inches in diameter, a foot or more long, and with a bore of one-half inch.
Flat blocks are apt to lie closely together in the fire, and obstruct the draft. A fire-place, constructed properly for burning them, should be shallow, not admitting of more than two or three layers being superposed. According to the bulkiness of the peat, the fire-place should be roomy, as regards length and breadth.
Fibrous and easily crumbling peat is usually burned upon a hearth, i. e. without a grate, either in stoves or open fire-places. Dense peat burns best upon a grate, the bars of which should be thin and near together, so that the air have access to every part of the fuel. The denser and tougher the peat, and the more its shape corresponds with that usual to coal, the better is it adapted for use in our ordinary coal stoves and furnaces.
5.—Burning of broken peat.
Fig. 1.—STAIR GRATE.
Broken peat—the fragments and waste of the cut or moulded blocks, and peat as obtained by plowing and harrowing the surface of drained peat-beds—may be used to advantage in the stair grate, fig. 1, which was introduced some years ago in Austria, and is adapted exclusively for burning finely divided fuel. It consists of a series of thin iron bars 3 to 4 inches wide, a, a, a, ... which are arranged above each other like steps, as shown in the figure. They are usually half as long as the grate is wide, and are supported at each end by two side pieces or walls, l. Below, the grate is closed by a heavy iron plate. The fuel is placed in the hopper A, which is kept filled, and from which it falls down the incline as rapidly as it is consumed. The air enters from the space G, and is regulated by doors, not shown in the cut, which open into it. The masonry is supported at u, by a hollow iron beam. Below, a lateral opening serves for clearing out the ashes. The effect of the fire depends upon the width of the throat of the hopper at u, which regulates the supply of fuel to the grate, and upon the inclination of the latter. The throat is usually from 6 to 8 inches wide, according to the nature of the fuel. The inclination of the grate is 40 to 45° and, in general, should be that which is assumed by the sides of a pile of the fuel to be burned, when it is thrown up into a heap. This grate ensures complete combustion of fuel that would fall through ordinary grates, and that would merely smoulder upon a hearth. The fire admits of easy regulation, the ashes may be removed and the fuel may be supplied without checking the fire. Not only broken peat, but coal dust, saw dust, wood turnings and the like may be burned on this grate. The figure represents it as adapted to a steam boiler.