The proof-stick (Fig. 1324) is simply a brass or gun-metal tnbe, which is driven from the upper part of the side of the vaeuum-pan down an aperture made of the samc size as the rod. When it renehes the bottom, the tube is twisted half round by the cross-handle, and opens a communication between the end of the tube and the syrup. lo the end of the tube is a groove, into which the syrup enters; the handle is half-turned again, the tube ia drawn out, and the entrance is closed as before. The liquor can thus be examined without destroying the vacuum in the pau. The sight glass is shown in Fig. 1325 : a, gnn-metal rings ; b, vacuum pan ; c, leaden ring ; d, Fin. bolt ; e, glass plate. Figs.
1326,1327 show a side-view and plan underneath of a alide.
It consists of a gun-metal cup and slide a, and wrought-iron lever-bar b, fitted with bearings, and of the form and dimen sions shown.
Curing.—The aticky mass of impure sugar-crystale ob tained from the vacuum-pan bas to undergo treatment which will separate tbe crystals in a pure white state. The old methods of drainage are described under the head of Cane-sugar ; in the beet-sugar industry, centrifugal machines aro now exclusively employed for the first operation: their principles and construction are detailed under Cane-sugar and Refining.
First, Second, and Third Sugara.—The centrifugal charged with the dirty crystalline mass is made to revolve rapidly till the colour has changed to reddish, when, without stopping the rotation, a email quantity of clairce (puro syrup at 30° D.) is poured in ; the result of this is a clear-yellow ti [Ain the whole mass, where upon dry steam is in jected, and soon the sugar becomes per featly white. This is termed sugar of pre Mier jet (" firat throw ing"). About # of the total sugar re ooverable in a crystal line form is thus ob tained. The liquid flowing away, contain ing the remaining # of crystallizable sugar, besides the uncrystallizable, is run into large tanks, reheated, filtered through animal charcoal, boiled to a stringy consistency, and stored in cieterns during the whole period while the first sugars are being cured. It is then passed through centxifugals, either alone, or with the addition of a little pure syrup, and thus affords a certain quantity of second sugars. The molasses drained off in the centrifugals is stored in immense tanks iu a room heated to 40° (104° F.), termed the salle des emplis (" filling room"). At the end of a year or so, this molasses is put through a centrifugal, and yields third sugars, with which are crystallized large proportions of saline impurities.
Yields.—The results ordinarily obtained in malng beet-sugar are :-100 lb. of beet afford 10 lb. of raw (uncured) first sugar, which loses 50 per cent. of its weight in the centrifugal, thus leaving 5 lb. of first sugars. The flowings from the first sugars yield 881 per cent. of raw second sugars,
whioh, after curing, furnish 371 per c,ent. of their weight of second sugars, or 11 lb. on the 100 lb. of beetroot. The curing of the second sugars gives a very variable quantity of molasses, which renders up 19-20 per cent. of its weight of sugar, or about 1 lb. of third engin on the 100 lb. of beetroot. The molasses proper contains 50 per cent. of eugar, and as it amounts to 3yer cent. of the beet, it carries away 11 lb. of sugar on the 100 lb. of beet, bringing the total yield of sugar to 81 per cent., out of the 10 per cent. originally contained in the roots, the 1/ per cent. difference representing losses during rnanufacture. Thus, 100 lb. of beetroot give :— Thus tbe average yield of crystalline sugar from the beet is 7 lb. on the 100 lb. of root, or T7r, of what the root contains ; while the final molasses takes away as much sugar (which is lost so far as its sugar is concerned) as is represented by the actual yield of second sugars.
The Molasses.—The average composition of final beet-molasses is :—Sugar, 50 per cent. ; non saccharine matters, 30 ; water, 20. Of the 30 parts non-saccharine matters, 10 are inorganic substances, principally potash ; the other 20 parts are organio bodies, various acids united to the potash. and other bases, compounds derived from the decomposition of the albumen (pectose), " betaIne," and many other substances which have not yet been isolated. These 30 parts of non saccharine rnatter contain 51 per cent. of potash, and 1'8-2.0 per cent. of nitrogen in combination. The annuul production.of final beet-molasses in continental Europe is estimated at 250,000 tons, representing 125,000 tons of sugar, 13,750 tons of potash, and 4500-5000 tons of nitrogen.
Until recently, the recovery of the 50 per cent. (125,000 tons) of sugar has not been attempted. The ordinary methods of utilizing the molasses have been (1) to convert the sugar present into alcohol by fermentation (see pp. 203-4), and (2) then to carbonize the residuary matters after the distillation of the spirit, and operato upon the ash to obtain the salts, principally carbonate of potash (see pp. 257-9). Somc 12,000 tons of potash were extracted from beet-molasses in this way, in 1875, in 18 factories situate in France, Germany, Belgium, and Austro-Hungary. These modes of utilizing the molasses arc not the most rational, inasmuch as alcohol can be produced much more cheaply and advantageously from starch. Several methods have been proposed for extract ing the sugar contained in the molasses. The most important of these are Dubrunfaut's " osmosis" process, largely adopted in Bussia, Germany, Belgium, and France ; Scheibler's " elution " process, renowned in Germany ; and various plans devised by Seyferth, Manoury, and others.