In France a good yield of acid is usually the main point, and the apparatus shown in Fig. 22 is extenaively employed. The charge of wood is arranged in a eylindrical wrought-iron retort A, of a capacity of about 6 cubic yards. Near the top of this cylinder, and at the side is a short exit pipe B for the gases, tapering for adaptation to a connecting pipe. The mouth of the retort is closed by a strong iron cover, which is well lilted, and the whole retort then hoisted into the brick furnace C, in the side of which is an opening to fit the exit pipe from the retort. Over the whole is embedded n cover of brickwork or other suitable material. At D is the fireplace. Heat being applied, the charge is first thoroughly dried, the connecting pipe is then &cat and carefully lilted, and tbe products of 2 distillation carried into the condenser. This is usually after the manner shown in Fig. 10, except that instead of a flow of water falling over the sets of pipes, the,se are themselves " jacketed " with pipes about 4 in. larger in diameter than themselves, and carefully closed at the ends. Water is conducted from a cistern set upon- a higher level, enters the lowest jacket E, rises through the small connecting pipes, and finally passes off at G. The uncondensed gases are carried through a pipe H to the fireplace and utilized as fuel, being evenly distri buted under the retort by a rose end and regulated by means of a stop-eock. When the flow of liquor ceases, and the connecting pipe between the con denser and the retort cools down, car bonization ia complete. The retort is then hauled out of its seat in the furnace and another charged retort substituted for it. Sometimes conden sation is effected by simply carrying the gases through a long arrangement of naked pipes, the heat passing off by radiation ; or by eonducting them into a series of connected wooden chambers; but where economization of water is not an important object the arrange ment first described is most esteemed.
-Another apparatus of very conve nient form and extensively used is that of M. Kestner's. The drawing, shown ia Fig. 23, will be readily understood after a study of our own wrought iron boxes or ovens of Gloucesterahire and South Wales. The retort may be made of either wrought-iron or cast imn plates bolted together.
In Germany and Belgium, in dis tricts where a good yield and quality of charcoal are &idly desired, the furnaces of Schwartz and Reichenbach axe esteemed and largely used. These are built of fire brick, and are often of great capacity, up to 5000 or 6000' cubic feet. Schwartz's furnace resembles an ordinary English coke oven, and the process followed is very similar to tbat of coke or lime burning, the fire traversing the whole of the interior of the furnace, but with the admission of only su.icient air to carbonize tbe wood. A free draught is secured by making " flues " with the larger pieces of timber and filling in the smaller pieces loosely ; in this way, too, an even distribu 'tiott of the fire and heat is established. The products of distillation pass oil' through openings near the bed of the furnace into convenient receptacles and condensers. It is known when the
carbonization is complete by the smoke issuing from the chimney turning from black to a bluish white. After being left to cool for about twenty-four hours, a little water is sprinkled over tbe charcoal fmm holes in the top of tbe furnaces, hitherto kept closed, and the whole mass raked out.
In Reichenbach's furnace, which is squara, carbonization is effected by beating io redness a series of pipes or flues about 12 in. in diameter, which are carried through the sides of the furnace, and doubled back again. The products of distillation pass off, as in the case of the furnace of Schwartz, through openings at the sole of the furnace, whence they issue into canals and pipes in which the tar is deposited and the acetic acid and other volatile products condensed. Reichen bach's oven is shown in Fig. 24 in section. The method of working will be apparent. The best charcoal, i. e. the most evenly carbonized, is obtained from Schwartz's apparatus.
In Russia and Sweden it is usual to carbonize in conical-shaped pits with a vessel placed along side, but at a slightly lower level, in which all the tarry and acid products collect. The process is carried on chiefly for the sake of the tar,—coniferons woods, yielding 12 or 13 per cent. as against 8 or 9 per eent. from foliaceous woods, being selected, and only an inferior charcoal produced.
In some parts of France and Germany .where there is a rank growth of heather or brushwood, the following process is occasionally adopted :—the material, the cost of which is the expense of cutting, is packed into raorts of wrought iron, ,,liaped like an inverted cone, and is set on fire, only just sufficient air being admitted through convenient openings to effect carbonization. The smoke and products of distillation pass off through a bent tube at the apex of the cone, and are conducted iuto suitable condensers and settlers.
Schwartz's somewhat peculiar process for obtaining acetic acid from wood may also be noticed. cuts up the timber into small pieces and arranges it upon bogies in such a way as to allow a current of air to pass freely in all directions through the mass. The bogies are then ruu into shaped ovens, all outlets are closed, and heat applied externally. Tho hut air within the oven is driven through the wood by means of fans, and without any actual carbonization a large yield of a peculiar sort of firewood is obtained, and a certain amount of acetic acid and tarry matters. It is claimed for this process that the results are highly profitable, but it is difficult to see how the manifest loss of the products of distillation, which only complete carbonization effects, can be made up.
The third method of preparing acetic acid is by the distillation of certain metallic aeetatee — soda, limo, lead, or potash—with sulphuric or hydrochloric acid ; or, as in the ease of bivacctate of copper, by heat alone. The process usually employed on a large scale is the distillation of acetate of soda with sulphuric acid ; in this way the bulk of the pure acetic acid of commerce is prepared.