814 SODA. —Reactions in Black-ash Furnace.

to the chimney-end of the revolver, and observesthrough the “eye.” A bluish flame round the sameis one of the marks of that stage being reached.The object of “liming” (which formed one ofthe principal improvements introduced by Messrs.Stevenson and W illiamson) is this: to cause therevolver-balls, which are extremely dense and diffi-cult to lixiviate, to burst in the tank by the slakingof the caustic lime, and thus to open them sufficientlyfor a thorough lixiviation.

James Mactear, of St. Rollox, Glasgow , has in-troduced an improvement which is to do away withthe tedious operation of liming. It consists indropping in the total mixture of sulphate of soda,limestone, and coal at one time, the quantitiesof the latter being smaller than usual in ordinaryrevolvers; then, after the decomposition is com-plete, adding a small quantity of caustic lime (say5 per cent, of the sulphate), and quickly mixing it upwith the charge by rapid revolutions of the cylinder;the charge is then at once drawn. The advantagesof Mactear’s process consist in a saving of lime(in both forms), in a large increase of productionfrom a given size of plant, and less caustic soda inthe liquors, whilst the balls dissolve precisely as wellas any other balls, and have quite as little soda inthe waste (as low as T3 per cent. Na 2 0). As thetotal amount of “ waste ” is smaller than in ordinaryworks, the absolute loss of soda in it is also cor-respondingly less. This process, which seems to bea very great improvement, has been recently carriedout quite successfully.

In most works the usual way is still to “ lime ” theballs as above described. When the “ liming ” hastaken place the revolver is stopped, the sulphate andthe remaining third of the coal are tipped in, and theengine is started again with the slow motion. Itwill be observed that the proportion of mixing coalsis larger than in the hand-furnaces; this excess ofmixing coal serves partly for a more completedecomposition of the sulphate, and partly to makethe balls more porous. During the charging of thesulphate the damper is let down to avoid any stuffbeing carried away by the draught; but it is raisedagain after ten minutes. About twenty minutesafterwards the appearance of a bright yellow flameround the working hole shows that the sulphate isnow melted, and the slow motion is now changedfor the quick one, say two revolutions per minute.The revolution is then continued till the workmanjudges from the appearance of the charge that it istime to finish. The consistency and colour of thecharges, and the bright yellow flames (“pipes”)darting especially from those parts adhering to the“ breakers,” offer the necessary data for his judg-ment. This last stage takes about half an hour.The engine is now allowed to run at full speed fortwo or three revolutions, so as to gather up theball; the charging door is hooked on to a pulleyand chain and taken off, and on turning roundslowly the liquid ball runs into the bogies, of whicha sufficient number (ten or twelve), connected by abar of iron, have been ranged underneath on a

tramway, and which are slowly drawn away, bymeans of a winch, as they fill. The bogies are 4feet by 3 feet wide at the top, somewhat narrower atthe bottom, and 10 inches deep, and their projectingtops nearly touch one another as they stand in therow. Nine of them are generally filled at once, andby quickly turning the revolver round enough isgathered to fill another two or three bogies.

Including the necessary pauses for stoppages, theaverage time for finishing a revolver charge is notquite two and a half hours (in Mactear’s processmuch less). Generally ten charges are finished intwenty-four hours, equal to 15 tons sulphate of soda,or 90 tons per week of six days. Some state thatthey work as much as 115 tons per week; but theabove statement is authentic. Two men by day,and as many by night, do all the work about thefurnace, one of whom is only a common labourer.The saving in wages against ordinary furnaces thusamounts to Is. to Is. 3 d. per ton sulphate. Thereis undoubtedly an advantage in requiring only one-fourth of the skilled labour usual with hand-furnaces,and in dispensing altogether with the gross manuallabour of working the balls by hand tools.

The fire-brick lining of the revolver lasts aboutfour months, and takes a week for its renewal.

The consumption of fuel is always stated to beless in revolvers than in hand furnaces for the samequantity of sulphate balled; the saving is differentlystated from a quarter to a third of the total.

The appearance of revolver balls is very differentfrom that of hand-made balls. They show, directlyafter drawing, the “candles” or “pipes” equallywell; but instead of a swelling porous mass, theyare dense, and become very hard on cooling. If itwere not for the “ liming ” they would not bedissolved at all, and even as it is, they require muchmore energetic treatment (especially steaming) thanhand-balls. Until recently it was assumed that theyield of ash from a given quantity of sulphate wasless in revolvers than in hand furnaces ; but manu-facturers have learned the manipulations better, andnowadays the yield from revolvers, even if it beslightly less in the gross, exceeds that from handfurnaces decisively when the available alkali in thesoda ash is considered.

For the reasons stated—saving in labour, savingin coals, and superior strength of the soda ash—thepreference is now given to revolving ball furnacesin all alkali works large enough to use the same, inspite of the considerable first cost of the revolversin comparison to the hand furnaces.

Theory of the Reactions in the Ball Furnace .—The action which takes place when a mixture ofsodium sulphate, calcium carbonate, and coal isexposed to heat, as well as the reactions ensuingwhen the resulting “black-ash” is treated withwater, are evidently of a complicated character, andhave been very differently interpreted by differentchemists. Dumas supposed that, in the first place,the sodium sulphate and calcium carbonate reactupon each, other, producing sodium carbonate andcalcium sulphate:—