Italian Poplar „ .. .. .. .. 48.2 „ „ Larch „ .. .. .. .. 48.6 „ I) White Poplar „ .. .. .. .. 50.6 „ /1 The samples tested were in all oases freshly cut wood. As all kinds of timber are hygroscopic, the action of the air in abstracting the moisture is to a ecrtain extent neutralized. Probably wood for distilling purposes, stacked in the yard or kept in the open, does not lose on an average more than one-third of its water.
Roots of trees may be distilled with very fair results, but are liable to the great evil of dry rot, and are expensive to prepare and pack in the ovens. In the proper sizing of these and of large logs dynamite might be advantageously substituted for the gunpowder which is often employed.
Different woods of course give different yields of the various products ; broadly speaking, perhaps, the charcoal—due regard being paid to its after uses—determines the quality of timber selected rather than any other cousideration. If this product is destined for the manufacture of gunpowder, alder, willow, or dogwood is chosen ; if for tin-plating and heating purposes, the heay.er woods, oak and beech ; if for crayons, willow ; if for absorbing purposes, a dense wood— box or lignum-vita3. If it be desired to obtain chiefly a good yield of pyrofigneous acid, birch, final], and apple are the most esteemed. Firs, and other resinous trees, give good yields of the tar compounds and naphthas, but aro not very extensively employed. As the most generally useful weed, giving good yields of all products—charcoal, acid, naphtha, and tar—oak holds the first place, and beech the second. The gunpowder woods give poor yields.
When the wood is cut it is "peeled "—that is the bark taken off—and allowed usually to lie in the coppice until required for distillation, the bark being stacked for sale to the tanners. Soinet:ines the timber is removed and stacked at the works, but this twice shifting entails un neeessnry expense, and should be only resorted to in cases of enforced removal. The cutting and peeling are done either by day work or "on piece," at very varying rates. It may be estimated roughly that the bark pays for the preparation of the timber, and the cost of drawing to the ovens and cutting up may be averaged at 7s. per ton.
The average yield of timber may be taken at 15 tons per acre, and the average cost delivered to the ovens at 138. per ton. The yield and weight of bark varies very much with the quality of timber and the wetness or dryness of the season, but may be averaged at 2 tons per acre.
For removal, the timber is packed into "cords," of which there aro several descriptions. The " government," or " crown," cord is 27 ft. 4 iu. x 2 ft. 2 in. x 2 ft. 2 in., containing 128 cub. ft., but two other cords are largely used, one 8 ft. long by 4 ft. wide and 4 ft. high, and the other 16i ft. long by 2 ft. 2 in. high, and made up of pieces cut 2 ft. 2 in. long. The weights of these cords vary from 14 to 25 cat. The short pieces, 2 ft. 2 in. long, are almost invariably preferred in Wales, and timber used there is, as a rule, much smaller than in other parts of the country. The length of time that the timber is allowed to lie or to remain stacked varies with different circumstances, but it should not be put into the ovens green, or else a large amount of moisture has to be dealt with in distillation, and the labour and fuel costs are proportionately increased. It is also essential that
there shall be no dry rot or " taint " present. In South \Voles, where stacking in tho yard is common, this last point is too little regarded.
The ovens are cylindrical or square, of cast or wrought iron, and of varying dimensions, according to the experience and judgment of the individual manufacturer. A convenient and very general form is shown in Figs. 5, 6, and 7 ; Fig. 5 showing the front elevation and section of the ovens crossways, Fig. 6 the bank,- Fig. 7 the eection of an oven lengthways. Tho ovens here are in the form of cast-iron cylinders, 9 ft. long, 4 ft. in diameter, and It in. thick, set horizontally in brickwork, side by side, and forming any convenient range. A good-sized works will have eight such cylinders. The house shown in elevation and section, and built on the top of the range of ovens, is for drying the acetate of lime, the production of which usually forms a continuous process with that of wood distillation. For a further description of this, see under "Acetate °Crime." One end of the cylibder, where the charge of wood is introduced and with drawn, is closed by a strong cast-iron door, working on u hinge at the side (or preferably, and as in Fig. 5, at the top), and secured by a orosabar. For convenience sake this door may be hauled up by a chain and pulley set in the brickwork above. From the other or fire end of the cylinder issues a pipe, 9 or even 10 in. in diameter, which carries off all the gaseous products of distilla tien. Each cylinder is heated by a separate fire, shown at A, Fig. 6. The products of combustion pass through the pigeon-holed arch, circulate round the oven into flues which ruu under tho drying floor, ancrfinally escape up the stalk. The fireplaces should be 5 ft. long and 20 in. wide. In some works two er more cylinders are set to one fire, and occasionally the flues are in no way divided, but the flames allowed to intermingle. Both these plane are, however, open to serious objections, the slight economy of fuel and brickwork width they effeet being more than counterbalanced by the difficulty ef repairing a cylinder when it is laid ofE Moreover, if the flues are preperly arranged, and the drying floor is carefully constructed, the loss of heat up the chimney is comparatively slight. Some manufacturers prefer the cylinder ends projecting 2 or 3 in. from the briekwork, but it is very doubtful if any benefit accrues from such setting, and there is a dis tinct less of heat from radiation. It is better to let the fire end of the cylinder stand in about 5 in., as shown in the drawings, allowing for a 4i-in. brick wall to be built up and around the exit pipe. At B, Fig. 7, is shown an arrangement for drawing the charcoal as whole as possible, consisting of a sheet of stout iron fitting the interior of the cylinder transversely, but only reaching about half way up. When the cylinder is charged, this diaphragm is set back to the fire end, but when the operation is completed, and the door raised, the workman draws it towards him by means of a rod lying on the bottom of the cylinder, and with it the whole of the charcoal residue.