112

TIETOUTS.

The furnace used for burning tar is commonly the same as that used for other fuel, andis fed by a small continuous stream, conducted by a wrought-iron service-pipe, from a tankplaced on the top of the retort-benches, or other convenient situation, on to a sheet-ironspout projecting a few inches outside the furnace-plate, and into the furnace itself, as shownin Fig. 23, where it spreads over a “ breeze-bottom,” previously brought to a red-heat.

When retorts have been at work for some months, their interior surfaces become incrustedwith a hard carbonaceous deposit, approaching, in some of its properties, to plumbago. Inprocess of time carburet of iron and the more infusible parts of the coke form a thickercrust, which it becomes necessary to remove, to prevent the destruction of the retort, and toallow the heat to penetrate to the coal contained within. The removal of this substance wasformerly effected with great difficulty by crowbars, but it was afterwards found, that byleaving the retort open, and allowing the air to come in contact with the heated interior, thedeposit, is consumed. Mr. Kirkham, the engineer to the Imperial Gas Company, at theirFulham station, employs an air-blast for the purpose, which is both speedy and efficaciousin its operation. His method of conducting the process is as follows:—A cast-iron pipe,about three inches in diameter, is carried along the front of the benches, at a little distanceabove the upper retorts. At points in this pipe, directly over every retort, a screw and plugis attached, into which screw, when the plug is removed, a wrought-iron service, about aninch in diameter, can be fixed, and led into any open retort. The main pipe is connectedwith a blowing cylinder, worked by the steam-engine, so that a strong blast can be madeto impinge upon any part of the hard incrustation, which gradually yields to it, and maythen be removed without difficulty.

At the last meeting of the British Association of Gas Managers, held in Birmingham, apaper was read by Mr. T. H. Methven, of Bury St. Edmund’s, on the subject of scurfingretorts, which gave rise to much discussion, and many plans for removing the incrustationsof carbon were recommended. Most of them, however, were based on the same principleas Mr. Kirkham’s, of causing a current of air to impinge on the heated carbon, either byadmitting the air at one end of the retort and taking the lid off the ascension pipe at theother end, or, in short retorts, by introducing a pipe through the mouth-piece to the back.

The “ graphite,” as this consolidated carbon is called, has been applied as a substitute forplatinum and platinized silver for the negative plates of voltaic batteries. For that purposeit is cut into plates of various thicknesses, and it has been found to act as efficiently as thecostly metallic conductors.

Various plans have been adopted for clearing out the coke from the retorts. It is rakedinto a vault built for the purpose of receiving it; or it is emptied on the floor, and after-wards wheeled away; or it is raked directly into iron trucks. In all cases the hot coke issprinkled with water to quench it, otherwise when exposed to the air it would consume andbecome deteriorated. The action of water, however, tends to disintegrate the coke and todiminish its value, and it would be advisable to dispense with that practice, and suffocatethe fire by the carbonic acid generated by the coke itself. For that purpose it would onlybe necessary, when iron trucks are employed, to cover them with lids.

Having described the general construction of retorts, the manner in which they may be