CONCENTRATION AND GRANIILATION.—The cane-juice, reduced to the condition of a clear solution of sugar (with some few salts as impurities) in water, has next to be deprived of so much of its water as will permit the sugar to assume a solid (usually crystalline) form. This operation, termed concentration" and " granulation," has been described in principle on p. 1854. The inversion of sugar during concentration of cane-syrup is said to be prevented by the introduction of superphosphate of lime into the juice before boiling. There is no evidence as to the practical utility of this plan ; but phosphoric acid appears rather to aid the crystallization of sugar (see p. 1850), and the process would therefore seem to be based on good ground. Both heat and cold have been applied to the concentration of cane-syrup, but chiefly the former.
Heat.—The means by which heat is applied to the evaporation of cane-juice may be described under five separate heads, according to their principles ; —(a) Pans heated by fire, (b) pans heated by steam, (c) film evaporators, (d) vacuum-pans, (e) bath evaporators, (f) Fryer's concretor.
a. Pans heated by Fire.—The earliest and crudest system of evaporation was the "copper wall," or " battery of open pans called " teaches " (taehes, tayches, &a.) The first two pans of the series are the clarifiers ; thence the juice flows into the teaches, sheet-copper pans set in masonry on a descending plane. As the juice concentrates, each lower pan fills up with liquor from the one immediately' above it, until the density of the liquor in the " striking-teach " permits Ilgranulation, when the mass is ladled into shallow wooden vessels, and conveyed away to be " cured." By ,the oldest method, the liquor was ladled throughout the series. More recently an improvement was introduced, consisting of a copper dipper, fitting inside the striking-tcach, and having at the bottom a large valve, opening upwards and worked by a 1,t. er. The dipper is attached to a crane, which commanda the striking-teach and the gutter leading to the coolers. This greatly economiaes time. The furnace for heating the series is set under the striking-teach ; the heat passes by flues to the chimney or to the boiler-flue.
In working a battery, the difficulty is determining the exact moment when the boiling of the "aling " in the striking-teach must cease, i.e., when to make a " akip ;" great skill and experience are required to suit each kind of juice. The main point ia to bring about crystallization in the sling in as great mass as possible after it cools : if the aling be taken out too soon, there will be only a few large irregular crystals, and a quantity of sugar will be left in the molasses ; if the sling be boiled too long, a aticky mass of tiny crystala and Byrup will result, from which the molassoa can only be drained off with great difficulty, and from which it is inipossible to obtain clean, dry, and hard cryatal:, An experienced " wall-man " knows the approach of the striking point ; but a good test is the following :—Pour a spoonful of the boiling sling into a glass of clear water ; if, aftir s, minute's cooling, the sling can be forraed into a ball which does not stick to the fingers, and slightly flattens itself on the bottom of the glass on being dropped in, the correct period has arrived for striking.
The continued use of the copper-wall is au illuatration of the backwardness of the cane-sugar industry in many places. Its drawbacks are :—(1) Waste of fuel ; (2) tho amouut of labour required and length of time occupied ; (3) considerable vvaste of liquor in the eloppy manipulation ; (4) the proportion of molasses produced is intensified by the churning-up of the liquor and consequent admixture of air, and by the irregular and uncontrollable action of the beat upon the surfaee of the metal with which the liquor ia in contact. The temperature prevailing in the striking-teach is not less than 110°-113° (230-235° F.) in any' part, and much greater at the bottom of the mass. It is therefore not surprising that liquor showing 10 per cent. of inverted (uncrystallizable) sugar in the first pan, should have 22-23 per cent. by the thne it is finished in the atriking-teach.