Chambers's encyclopaedia; a dictionary of universal knowledge . oducingmixtures, and for making various chemicals. From iiny of these salt-cake furnaces the hydro-chloric acid gas is led away by pipes or flues tocondensing towers sometimes 100 leet high, andfilled with pieces of coke. The acid vapour enters atthe bottom of the tower, and in ascending throughthe piled coke meets with a descending streamof water from the cistern on the top by whichit is absorbed, and Hows away as liquid acidthrough a pipe at the base of the tower tostock-cisterns. Strong hydrochloric acid, wliich ischielly used
Chambers's encyclopaedia; a dictionary of universal knowledge . oducingmixtures, and for making various chemicals. From iiny of these salt-cake furnaces the hydro-chloric acid gas is led away by pipes or flues tocondensing towers sometimes 100 leet high, andfilled with pieces of coke. The acid vapour enters atthe bottom of the tower, and in ascending throughthe piled coke meets with a descending streamof water from the cistern on the top by whichit is absorbed, and Hows away as liquid acidthrough a pipe at the base of the tower tostock-cisterns. Strong hydrochloric acid, wliich ischielly used in the manufacture of BleachingPowder (q. v.), is easily obtained by good condens-ing appliances either from the rotatory pan furnaceor from the pan of a stationary furnace, but theacid from the roaster gas is usually weak. TheAlkali Acts of 1863 and 1874 make the condensa-tion of nearly the whole of the gaseous hydro-chloric acid produced at soda-works imperative. Conversion of the Sulpliatc of Soda into Black-ash.—The sulphate of soda is roasted with coal. Fig. 2.—Kotating Furnace for making SulphatL- iit .->cjiia:A, iron imii for containing cliar^-e ; B, hopper, with balanced cone for charRlng;C, fireplace; D, one of the stirrers; E, self-acting arrangement for discharg- and limestoneto produce crude carbonate of this operation the oxygen of the sulphate com-bines with carbon furnished by the coal to formcarbonic oxide, which escapes into the air. Theremaining sodium sulphide interchanges combina-tions with the carbonate of lime (limestone), form-ing carbonate of soda, easily soluble in water, andcalcium sulphide, which is insoluble. The actionof tlie carbon in reducing the sulphate of soda tothe sulphide is shown by the equation Na^SOj -f C4 = Na,S -f 4C0. The furtlier change which occurs is thus repre-sented : Na.,S -I- CaCOj = -f CaS. The proportions of the materials as now used arethe same as those lirst recommended by Leblanc—viz. sulphate of sod
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