SO DA.— Black-ash.
Revolving Furnace. 813
shaft of 5jj inches diameter, which gives the quickmotion; the slow motion is produced indirectlyby a lower gearing. It is steadied by a fly wheleof sufficient weight. The whole is fixed on a set ofbed plates, of box-girder form, all bolted togetherand bolted down upon a solid stone or concretefoundation, so as to form one entire and completebed.
On one side of this cylinder is the fire-place; onthe other side, the dust chamber and the pans. Thefire-place is sometimes not provided with grate bars,and serves only to produce a flame from generatorgas; but in the great majority of cases direct firing ispreferred. In that case the fire-place is about 6 feetto 6 feet 6 inches long (in the same direction as theaxis of the cylinder) and about 4 feet 6 inches wide—both inside measurements. The bars run across, fromthe front to the back, and two stoke holes in thefront serve for charging the coals. There is no fire-bridge in the usual sense, but only a hole exactlycorresponding to the “ eye ” in the cylinder. Thereis a space of about 12 inches between them, whichis partly filled by an iron ring lined with fire-brick,and suspended from above; but the air has freeaccess round this ring, so that a constant indraftinto the furnace takes place through the eye, andassists the complete combustion of the gas withinthe revolver. The eye on the other side of thecylinder is so arranged that the man in charge canlook into its interior, and observe the state of thecharge constantly. From that side the flame passesfirst into a capacious smoke chamber for the reten-tion of flue-dust, and is then divided in two parts,in order to heat two boiling-down pans runningparallel to each other. These are about 28 feet longand 8 feet broad each, with four or five drawingdoors and drainers running along their fronts, likethose described above in connection with the ordi-nary ball furnace. Frequently the pans, as well asthe drainers, have a partition running across them,and dividing them into a larger and a smaller section.The red liquor is then pumped back exclusively intothe smaller section, and the salt drawn out of itgives weak and coloured ash, whilst that from thelarger section, which is kept quite free from redliquors, is of very great strength (55 to 56 per cent.)and purity. As the quantity of red liquor is, ofcourse, very large, it is usual to provide a specialsteam pump for the same. Sometimes the settlingpans are fixed on the arches of the boiling-downpans proper, in order to receive some preliminarywarming. The flue to the chimney is, as usual, pro-vided with a damper, and it being necessary to havevery strong draught at command, as a rule no otherflues are allowed to go into the same chimney.
The lining of the revolver proper is barrel-shaped—viz., 9 inches thick at the ends and 4^ inches inthe centre. Two horizontal rows of fire-clay lumps(“ breakers ”) project over it, to the extent of 9inches near the ends and 14 inches at the centre.These serve for mixing the charge thoroughly, andturning it over during the revolution. They actlike cascades when the stuff has been liquefied.
It may be of interest for some readers to seewhat the cost of such an apparatus is; an estimatefrom the above-mentioned firm runs as follows:—
Revolving furnace, engine, and gearing,! cjj 2 Q
Cement concrete foundations for same, . 60
Boiling-down pans,. 140
Drainers, . 75
Drainer, pump, and pipes, . 65
Plates, binders, and bolts, . 160
Mason work, including cement concrete') 220
flooring, . )
Twelve ball bogies,. 54
Three chalk waggons, . 43
£1937
To this must be added the cost of the overheadrailway, of the elevator for the materials, and ofsulphate crushers, where the latter are used.
Much larger revolvers, built in a barrel shape, arenow being erected at Glasgow .
Each revolver must necessarily have its owndriving steam-engine, as it is imperative to haveit entirely under control, so as to drive it slow orfast, stop it and reverse it at a moment’s notice,without being hampered by any other work attachedto the engine. One single engine, however, sufficesfor the purpose of crushing the sulphate for severalrevolvers (which is in some works avoided bymerely screening it), and for elevating the materialsto the railway running over the revolvers. Gene-rally, the sulphate, chalk, and coals are each filledinto conical waggons holding a full charge, about
5 feet X4 feet X 4 feet 6 inches; these are constructedso as to empty their contents at once through ahopper into the charging hole of the revolver bydrawing a bolt which holds up their bottoms. Thecharges are not the same in every works, as the size ofthe furnace and the nature of the material varies.
For the size of furnace described, and when usingchalk, the charge is as follows:—30 ewts. of sul-phate, 33 to 35 cwts. of chalk, and 17 to 19 cwts. ofcoals, according to quality. The sulphate musteither be crushed, or, which is the cheaper course, .it is thrown through a screen with half-inch meshes,and only the lumps are broken. The chalk is usedwithout crushing or drying, this being unnecessary, as,when the damp chalk is tipped into the bright red-hot revolver, the moisture is almost instantaneouslyconverted into steam, and causes the lumps of chalkto fly into fine powder with the force of a smallexplosion. The coal is divided: two-thirds arecharged with the chalk and one-third subsequentlywith the sulphate. The mixture of a Lancashire work is stated: 30 sulphate, 27 limestone, 17 coal.
First of all, the chalk is tipped into the revolver(whose charging hole has, of course, been broughtstraight under the hopper), and two-thirds ofthe coal, as before mentioned. The engine is thenstarted, and the slow motion is used, say one turn infive minutes. After an hour and ten or fifteenminutes the stage of “liming” is reached; that is, acertain portion of the chalk has now been causticized.
The exact appreciation of this moment is the princi-pal object of the revolver - man, who sits opposite