The great advantage of Exter's and Elsberg's method consists in avoiding what most of the others require, viz.: the expensive transportation and handling of fresh peat, which contains 80 to 90 per cent. of water, and the rapid removal of this excess of water before the manufacture. In the other methods the surplus water must be slowly removed during or after condensation.
Again, enough peat may be air-dried and stored during summer weather, to supply a machine with work during the whole year.
Its disadvantages are, that it requires a large outlay of capital and great expenditure of mechanical force. Its product is, moreover, not adapted for coking.
B.—Condensation without Pressure.
The methods of condensing peat, that remain to be described, are based upon radically different principles from those already noticed. In these, little or no pressure is employed in the operations; but advantage is taken of the important fact that when wet or moist peat is ground, cut or in any way reduced to a pulpy or pasty consistence, with destruction of the elastic fibres, it will, on drying, shrink together to a coherent mass, that may acquire a density and toughness much greater than it is possible to obtain by any amount of mere pressure.
The various processes that remain to notice are essentially reducible to two types, of which the French method, invented by Challeton, and the German, invented it appears by Weber, are the original representatives. The former method is only applicable to earthy, well-decomposed peat, containing little fibre. The latter was originally applied to fibrous moss-peat, but has since been adapted to all kinds. Other inventors, English, German, and American, have modified these methods in their details, or in the construction of the requisite machinery, rendering them more perfect in their execution and perhaps more profitable in their results; but, as regards the essential principles of production, or the quality of product, no advance appears to have been made beyond the original inventors.
a. Condensation of Earthy Peat.
Challeton's Method consists essentially in destroying the fibres, and reducing the peat by cutting and grinding with water to a pulp; then slowly removing the liquid, until the peat dries away to a hard coherent mass. It provides also for the purification of the peat from earthy matters. It is, in many respects, an imitation of the old Dutch and Irish mode of making "hand peat" (Baggertorf), and is very like the paper manufacture in its operations. Challeton's Works, situated near Paris, at Mennecy, near Montanges, were visited in 1856 by a Commission of the Agricultural Society of Holstein, consisting of Drs. Meyn and Luetkens, and also by Dr. Ruehlmann, in the interest of the Hanoverian Government. From their account[22] the following statements are derived.
The peat at Mennecy comes from the decay of grasses, is black, well decomposed, and occasionally intermingled with shells and sand. The moor is traversed by canals, which serve for the transport of the excavated peat in boats. The peat, when brought to the manufactory, is emptied into a cistern, which, by communicating with the adjacent canal, maintains a constant level of water. From this cistern the peat is carried up by a chain of buckets and emptied into a hopper, where it is caught by toothed cylinders in rapid revolution, and cut or torn to pieces. Thence it passes into a chamber where the fine parts are separated from unbroken roots and fibres by revolving brushes, which force the former through small holes in the walls of the chamber, while the latter are swept out through a larger passage. The pulverized peat finally falls into a cistern, in which it is agitated by revolving arms. A stream of water constantly enters this vessel from beneath, while a chain of buckets as rapidly carries off the peat pulp. All sand, shells, and other heavy matters, remain at the bottom of this cistern.
The peat pulp, thus purified, flows through wooden troughs into a series of basins, in which the peat is formed and dried. These basins are made upon the ground by putting up a square frame (of boards on edge,) about one foot deep, and placing at the bottom old matting or a layer of flags or reeds. Each basin is about a rod square, and 800 of them are employed. They are filled with the peat pulp to the top. In a few days the water either filters away into the ground, or evaporates, so that a soft stratum of peat, about 3 inches in thickness, remains. Before it begins to crack from drying, it is divided into blocks, by pressing into it a light trellis-like framework, having thin partitions that serve to indent the peat in lines corresponding to the intended divisions. On further drying, the mass separates into blocks at the lines thus impressed, and in a few days, they are ready to remove and arrange for further desiccation.