SXJ GAR. —Beet-root. Concentration.

897

choked. Further trials are, however, being nowmade by Bowing, the patentee of a new form ofthe apparatus.

Charcoaling .—The thin defecated and carbonatedjuice, still containing a minute percentage of limeand all the potash and soda originally present,together with a considerable proportion of non-saccharine organic bodies, is then passed througha deep bed of animal charcoal. The cisterns ofchar filters are usually about 15 feet deep, and onlyabout 2^ to 8 feet in diameter, but have otherwisethe form and disposition of parts common to thoseused in the refinery.

The char is used in grains or fragments nearly aslarge as small beans; and before the juice is allowedto flow into it, it is thoroughly steamed out, and isused hot. As such precautions are found in prac-tice to be necessary for the beet juice, though notfor the thick liquors of a refinery, it is worth whilefor those manufacturers of cane sugar who havemet with difficulties in their attempts to employanimal charcoal, to take this hint from their rivals.

As an example of the amount of purificationeffected by char on the thin juice a determinationby Rabe may be cited. The juice defecated andcarbonated contained—

Tig. 2,

After Filtration,

8*0 per cent

Before Filtration.

Sugar,... 8*0 per cent.

Organic matter,.. 0*56 '•

Ash salts,. 059

0-48

0-46

Or the char absorbed 14-3 per cent, of the organicimpurities and 22 per cent, of the salts. The quan-tity of char used daily in German factories is about15 to 20 per cent, of the weight of the rootsworked up.

First Concentration .—The charcoaled “thin juice”is next concentrated by evaporation to about 20° B.To effect this the so-called “ double ” or “ tripleeffect” vacuum pan is employed. In this instru-ment the vapour (steam) rising from the boilingsolution in one pan is made to pass into the worms orheating tubes of the next, and the vapour from thesecond into the worms, &c., of the third. In theorythe number of pans so arranged, one after the other,might be largely increased with corresponding econ-omy ; but from various causes, stfch as loss of heatby radiation, &c., three are found to be as manyas can advantageously be worked in this way. InFig. 2 it will be seen that the worms of anordinary vacuum pan are here replaced by a steam-chest, which is traversed by a large number ofVOL. II.

vertical tubes which are open at top and bottom toallow the boiling solution to circulate freely. Thesteam for boiling is introduced into the steam-chestso as to surround the outsides of the boiling tubes.In other modifications of the apparatus the bodiesof the pans have a form similar to locomotive boil-ers, and, like them, are furnished with a large numberof horizontal copper tubes, which in this case con-vey the heating steam. In whichever form it isused, a fairly good vacuum is maintained in the thirdpan (about a 25-inch vacuum), a less vacuum in thesecond, and none in the first. In consequence ofthis the liquid in the first pan boils at about 100° C.,that in the second at about 15° C. lower, and that inthe third at 20° C. lower still. In this way the neces-sary difference in temperature between the heating113