Page:Encyclopædia Britannica, Ninth Edition, v. 10.djvu/101

Rh GAS 91 The cylindrical form of retort a (ﬁg. 2) was long in favour on account of its great durability, but it is not so well ﬁtted l'ori'apidde-. ~ ‘ composition of the coal as the ellip- tical 6, or Fig. 2. the ﬂat-bottomed or D-shaped retorts cl, which are now principally in use. Retorts are also made of a rectangular section with the corners rounded and the roof arched. lilliptical retorts are varied into what are called ear-shaped or kidney—shaped c, and it is not unusual to set retorts of different forms in the same bench, for the convenience of ﬁlling up the liaunches of the arch which encloses them. The length of single retorts varies from G to 9 feet, but they are now in seine cases made 191; feet in length and inches in internal diameter, these being charged from both ends. Exdery retort is furnished with a separate mouthpiece, usually of cast iron, with asocket b (ﬁg. 3) for receiving the stand-pipe or ascen- sion-pipe, and there is a movable lid attached to the mouth, together with an ear—bo.: cast on each side of the retort for re- ceiving the cars which support the lid. Fig. 3 shows a form of mouth- piece attached to the retort (1, and also the method of screwing the lid to the i.iioiitlipiece. That part of the lid which comes in contact with the edge of the mouthpiece has applied to it a lute of lime mortar and ﬁre clay, and when the lid is screwed up, a portion of this lute oozes out round the edges and forms a gas—tiglit joint. Except for small works, where the manufacture is iiiter— inittent-, and where, consequently, the retort heat has to be got up frequently, iron retorts are now little used. Clay retorts, which at present are in most general use, wear out quickly; they very frequently crack so seri.ously on the ﬁrst application of heat that they must be removed from the Fig. 3. bench before being used at all, and in scarcely any case . are they in action perfectly free from cracks. Numerous attempts have been made to introduce retorts built of brick _; but the difliculty of making and keeping the joints air- tight has proved a serious obstacle to their use. In the FIG. 4.——Hislop’s Brick Retort. brick retort made of Glenboig Star ﬁre-clay, according to the‘ plan ‘of Mr James Hislop, it is clai.med that the difhculty is surmounted, and that both the retort and its setting present great advantage and economy. These brick retorts (ﬁg. 4) are .O~shaped, 9 feet long and with diameters of 22 and inches, set four in an oven to one uiiarched furnace, as in ﬁg. 7. carbonize 500 tons cannel coal, or 2000 tons per even of four, without any repairs whatever. Decayed bricks may be removed from these retorts and new ones inserted, and when thoroughly repaired they are again equal to new. Thus the durability of each retort is so great that they are calculated to cost about gth of a penny per 1000 cubic feet of gas generated, as against 1d. in the case of moulded retorts, and 7d. with iron retorts, for the same production of gas. In the Hislop retort the arched bricks are made plain, without groove or rebate joints—being thus stronger, more readily put together, and also cheaper. Carbon does not collect so rapidly on brick retorts as on those of clay, the bricks being harder pressed and better burned. On ﬁrst lighting brick retorts, a charge of coke, breeze, and tar mixed makes them perfectly gas-tight. Retort Setting.—A furnace or bed of retorts is composed of a group or setting, heated by a separate ﬁre. The furnace is lined with the most refractory ﬁre—bricks, and while the whole brickwork is made of such strength and solidity as ensures the safety of the retorts, the internal construction is so planned that the heat has the utmost possible amount of direct play on the retorts. The number of retorts to one furnace varies from 1 to 15, from 4 to 7 being the number most commonly adopted ; and these are variously arranged to bring them all as close to the furnace heat as practicable. In some retort-houses the furnaces are built in two stages or stories, from the upper of which the retorts are charged and drawn, while at the lower level the glowing coke is removed and quenched. The whole range of furnaces constitutes the retort bench, having a common ﬂue which leads to the chimney shaft by which the products of combustion are carried away. The gas—coal for charging the retorts is broken into fragments about 1 lb in weight or Figs. 5 (elevation) and 6 (section) illustrate the < thereby. E < FIG. 5. —-Elevation of Hislop’s Gas Retort Furnace. retort setting and arrangement of furnace and fines adopted by Mr Hislop for his brick retorts, i.ii which, by the use of ‘ centre blocks, as seen in the open front illustration (ﬁg. 7), the necessity for internal arching is avoided. _ Retort furnaces are commonly ﬁred or heated with a Each retort will, it is affirmed,, portion of the coke which forms one of the bye—products of