When the clarifier has a steam-coil or -jacket, little loss of time occurs, for as soon as enongh liquor is in the clarifier, st,eam is turned on so as to attain the desired tempemtnre by the tirne the vessel is full. Fire-clarifiers are discharged by a stopcock near the bottom, till the liquor begins to run muddy ; steam-olarifiers, by a valve in connection with a tube that rises 4-6 in. above the bottom, so as not to disturb the sediment.
This method is open to the objections that :—(1) Clarification is rarely attainable below the boiling-point of the juice, consequently the juice wants brilliancy and transparency, and minute floating partioles render the filtration unsatisfactory; (2) the floating matter is thrown up as soum during the concentration, causing waste of juice in the skimmings.
Dr. Shier's modification is as follows :—The strained juice is boiled briskly for 5 minutes, the senni being constantly beaten down. While boiliog, the proper quantity of temper-lime is added mixed with clay-batter, gypsum, or whiting-batter ; the boiling, stirring, and beating down are con tinued for a few minutes. Neutralization being effected, the whole contents are rapidly withdrawn into a subsides, and left till the coagulated flocculent matter has subsided. The clear juice is drawn off and passed through a filter into a cistern. Here, excess of lime is corrected by careful addition of dilute sulphuric acid. It is safest to cease adding acid when the alkaline reaction becomes extremely feeble. Were the lime in excess, the sugar would be dark-coloured ; were the acid in excess, tho grain would be fine and soft, and part of the sugar would become uncrystallizable. The addition of heavy matter to the temper-lime causes the impurities to form a sediment which may be filtered off, instead, of a scum which needs skimming. It is said to effect a great saving of juice. Clay-batter is prepared from stiff clay (containing as little sand and organio matter as possible), well dried, crushed to powder, and screened through a wire-gauze sieve of 10-11 threads per in. The sifted clay is mixed up Ntith clean water to the consi-tency of cream or batter. About 4-8 gal. of this batter, mixed with the cream of lime, go to 500 gal. juice. Gypsum or whiting usea in place of the clay must be in very fine powder.
Howard's process, strongly recommended by Wray, is as fellows :—The juice is striined and gently warmed ; for each 100 gal. of juice, 2 oz. of finely-sifted quick-lime, made into a cream with water, aro added ; tho whole is well stirred, and heated to 82' (180° F.), until a thick crust forms on tho surface, and shows a disposition to crack. This occupies 15-20 minutes after the addition of the limo ; if it is very slow, the heat may be raised to 93° (200° F.), but not boyond. When tho crust shows signs of cracking, the fire is stopped ; the liquor is allowed to rest for 10 minutes, and drawn off through a fine strainer into a "precipitator." Here the firing is urged as high as possible without actual boiling, the rising scum being constantly skimmed off. The liquor is then bailed,
continuing tho skimming for 10-15 minutes, after which, the " finings " aro well stirred in, and the boiling is prolooged for another 2-3 minutes, when the whole is thoroughly agitated, quickly run off into a subsiding-tank, and allowed to rest for 2-6 hours before passing through charcoal-filters into the evaporators.
The " finings " aro thus prepared. Well-burnt lime is slaked with boiling water so as to form a cream ; an equal bulk of water is added, and tbe mixture is boiled for some minutes, until the lime assumes tho appearance of fine curd; the extraneous matter is then washed away, and the lime and liquor are run through a fine sieve. About 2i lb. of alum for every cwt. of solid sugar (say 100 gal. of cane-liquor) is dissolved in 6 gal. of water, adding about 3 oz. of whiting (purified ohalk) for °Etc& 2i lb. of alum, the mixture being stirred until effervescence ceases. It is allowed to subside, and tho solution (containing sulphate of potash, which is very injurious to sugar) is drawn off from the precipitated matters (alutnina and sulphate of lime). After this, the precipitate is well shaken up with the prepared lime-curds, which are in such proportion that turmeric-paper barely changes colour by immersion in it, and recovers its yellowness when dry. The finings settle to the bottom of the vessels, and, after draining off the supernatant liquor, aro placed on blanket filters, until the mass contracts, and cracks on its surface ; the finings are then fit for use. Cane liquor is added in such proportion as will bring it to a creamy state, and then the whole is mixed equally into the liquor to be fined. The clarified cane-liquor remains for several hours before the bright liquor is drawn off. The object of the process is to procure sulphate of alumina free from potash and ammonia (see Alumina, p. 333). The alumina greatly assists the purifying action of the lime. (See Refining.) Bisulphite of lime.—The bleaching and cleansing action of sulphurous acid led to experiment upon its applicability to the defecation of cane-juice, and the first forrn in which it was employed was as a compound with lime, k-nown as bisulphite of lime. About 1 per cent. or less of solution of bisulphite is added to the juice immediately it is extracted, or even while it is being extracted. Heat is then applied, and after the juice hss been boiled and stirred for a few minutes, a mixture of cream of lirne and clay-batter is added. The exact quantity of cream of lime is ascertained by test (p. 1886), sufficient only being used to produce neutrality. After boiling for 5-10 minutes, and beating down the scum, the contents of the clarifier are run into a subside; and thence filtered out for concentration. The subsidence is not efficient without the addition of some weighting matter ; but the syrup has a very fine colour, and gives a superior-looking muscovado sugar. An objection is the high price of the bisulphite.