ALUM.—C RYSTALLIZATI ON.
the pipe, in seeking to escape through the aperturesin the funnel, dissolves the powder; the solutiontrickles to the bottom of the vessel at a temperature
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of 212° Falir. (100° C.). At the termination of theprocess a small quantity of undissolved basic alumis left in the funnel, which is added to the conccn-
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tratcd liquor ready for precipitation, and is redis-solved as before stated. During the time the flouris dissolving in the roching vessel, the crystallizersare being prepared, and the aluminous solution, ofa density about 1-485 to 1-515, is run into them byapjrropriate means.
The crystallizers are large wooden casks, 5 to 8feet high, 3 or 4 feet in diameter at the top, andtapering in a somewhat conical form towards thebottom. The staves of these casks are very strong,nicely adjusted, lined with sheet-lead, and held to-gether by means of strong iron hoops, which arehammered on when required for use, and may be aseasily removed.
Fig. 10 is a view of these casks arranged in thecrystallizing shed; over each a spout is fixed to fillthem with the liquor. Some of the casks are repre-sented as on the point of being charged, while inothers the crystallization is completed, and the stavesare being taken off. When the casks are charged,they are covered up, each with its own lid. Afterremaining undisturbed for four or five days, accord-ing to the state of the weather, the hoops areloosened and the staves removed; the crust of alumthen formed being sufficiently strong to resist thepressure of the interior liquor. In this state theyVOL. i.
are left for a fortnight, in order to allow the wholeof the crystallizable salt to form. Tlfe workmenthen pierce a few holes in the sides of the columnwith an axe, and the mother liquor in the interior
Fig- 10.
flows into the gutters in the stone floor, which con-duct it into an appropriate cistern, whence it ispumped up to dissolve fresh quantities of the pre-
22