COMPOSITION OP CANE-MICH.—Before detailing the many processes and apparatus used in making sugar, an idea must be gained of the natnre and characters of cane-juice. Mention has already been made of the strueture of the sugar-cane. Within the cells, is contained a sweet watery juice, a sugar-water holding a variable quantity of organic and mineral matters in solution. This is the juice whioh is extracted for the purpose of being Lunde to yield its sugar. The nature of the ingredients composing it is not liable to variation ; but thoir proportions fluctuate with tho soil and climate, the age of the eane, the portion of the cane affording the juice, and other circum stances. R. H. Harland states the composition of some cane-juices expressed front ripe canes grown in Queensland, as follows:— In general terms, cane-juiee consists of about 81 per cent. of water, 18 of sugar, 0.6 of organic matters, and 0.4 of inorganic (mineral) matters ; further, about 0.5-0 • 6 per cent. of the sugar in the juiee of ripe canes (it is much greater in unripe ones, as shown) is uncrystalliz.Lble. These substances are very intimately combined, but the juice is not of one constant quality through out the whole cane. Thus planters reject the tops of the canes before extracting the juice. Further, the juices eontained in the soft central (medullary) part of the cane are much rieher in sugar than those of the nodular (the " knots ") and cortical (the rind) portions. Conversely, the saline and organie matters (other than sugar) are in increasing proportion in the harder parts of the cane ; when an extra yield of juice, therefore, is obtained hy the exhaustion of the hai do- portions, the quantity is at the expense of the quality. This haa a bearing upon the question of the relative advantages of mills extracting only 60 per cent. and those getting 85 of the 90 per cent. of juice usually present in the cane.
It is now necessary to separately consider each eomponent part (or group) of the raw juice.
The Crystallizable and Uncrystallizable Smiar.—The artificial eonversion of uncrystallizable into crystallizable sugar remains an impossibility, though the latter can he readily n inverted" into the former. From experiments by Harland, it would seem that in the growing or ripening plant a conversion of unerystallizable into crystallizable sugar does take place, the proportion of the former being markedly decreased in juice expressed 8 days after the cutting. The occurrence of
uncryatallizabk sugar in the juioe works a twofold mischief :—(1) The uncrystallizable sugar is itself a loss, i.e. it has no value as sugar ; (2) its existence in the syrup so affects the remainder as to hinder, if not prevent, the recovery of an equal quantity of the crystallizable sugar in a saleable form, for the liquid containing the altered sugar has a treacly consistence, and cannot be con veniently deprived of its water by evaporation to such a degree as will leave the unaltered sugar in a saturated solution capable of clean crystallization on cooling. Practically, therefore, it may be said that every 1 lb. of sugar rendered uncrystallizable means a loss of 2 lb. of crystallizable sugar.
The chief cause of alteration in the sugar is fermentation of certain constituents of the juice, viz. the organic matters other than the sugar. The essential conditions are mainly access of air to the juice, and a moderately high temperature. Consequently fermentation begins in the living cane, when injuries (gnawing hy rats) admit air into the cells. Artificially, it is set up the moment the juice is extracted, and is maintained by the heat necessary for carrying on the manufacture, augmenting as the time is prolonged and the heat increased. Acids also provoke fermentation ; they are nearly always present in a free state, as shown by the juice giving a red colour to litmus paper. Hence the importance of rapid treatment at low temperatures, and with the least possible exposure. Fermentation does not commence in the juice while still in uninjured canes. In Louisiana, sound canes may be kept for 3-4 months after cutting, the only result being the loss of a portion of the water of vegetation. In the Philippines, sound cut canes may be kept for a week at least, despite the high temperature of an Eastern tropical summer. This seems to indicate that canes could be kept and transported long distances without undergoing loss of crystallizable sugar ; but it applies only to sound canes, and the result might he different in cases wlaere the rind was cracked or eaten into. Obviously something also depends upon the climate, as in the W. Indies and Demerara, the juice must be expressed within 48 hours after cutting, to prevent an excessive inversion taking place ; this is retarded by antiseptics, and salicylic acid is now much used with this object.