938

SULPHURIC ACID.— Towers.

The mixed gases from the burners pass along alarge metal pipe lined with fire bricks to a lead

Fig. 5. Fig. 6.

Fig. 7.

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tower, called a denitrating column, or Glovertower (shown in Figs. 5, G, and 7), and constructed

of lead about 14 lbs. to 31 lbs. to the foot, and sayabout 20 to 25 feet high X 10 feet square. Thistower is filled with bricks or fire-clayblocks to a certain height from thebottom, and then with flints or hardcoke to within about 2 feet of the top.The hot gases from the burners, stand-ing about 350° Fahr., pass into thecolumn at a, and are met by a streamof nitro-sulphuric acid from the Gay-Lussac absorbing column (which itthoroughly denitrates), and also astream of weaker acid from the cham-bers ; the gases finally pass into thevitriol chambers, considerably cooled,by the flue, b. It is usual to havetwo cisterns for the supply of the acid—one to contain the nitro-sulphuricacid, and the other the weak acid.The two streams of acid are made tomeet on entering the top of the column,and the weak acid assists in liberatingthe nitrous fumes held in the strongeracid, and each acid is in turn con-centrated on its way through thecolumn, and runs out at the foot atabout 150° T. (1-750 specific gravity),and after cooling is again available forthe absorption of more nitrous acid.The weak acid referred to above, thesulphurous acid, and the heat in thecolumn, all act together in separating from thestrong acid from the absorbing column its nitrousgases for use in the chamber. The acid is cooledby causing it to run through a long coil of lead pipeabout 2 inches in diameter, which is placed in atrough, through which continually pours a runningstream of cold water. Another advantage derivedfrom this tower is, that all the evaporated water iseconomically employed as steam in the chambers.

The nitrate of soda used at the burners, with awell-regulated Gay-Lussac apparatus at work, neednot be more than 1-75 to 2 per cent, when usingpyrites testing about 47 per cent, of sulphur, orabout 3-72 to 4-25 per cent, on the sulphur in theore ; whereas, before the Gay-Lussac apparatus wasused, the nitrate of soda was about 4 per cent, onthe former and 9 to 10 per cent, on the latter. Withall the care taken, however, a certain weight ofnitre, or its equivalent in nitrous acid, is almostnecessarily lost. This loss varies in different works,but may be said to be from 3 to 6 per cent.; andthe chief sources of loss occur in the acid on thefloor of the chamber, which absorbs some nitricoxide from a small escape at the exit pipe of theGay-Lussac column, already referred to, and asmall waste at the burners. The Glover toweris sometimes so placed that the nitro-sulphuricacid from the Gay-Lussac tower, and the weakacid from the chambers, will both run to it withoutpumping, and are mixed as they enter together atthe top.

The final stage in the operations connected with