The cane, therefore, may be said to yield 90 per cent. of juice, which latter contains from 18 to 20 parts of pure sugar. However, the actual quantity obtained is rarely if ever more than 1 lb. of sugar to a gallon of juice, or 10 per cent.; and much more frequently only 8 per cent.
A large part of this loss is due to the prolonged exposure of the cane juice during its repeated boilings to heat, whereby a large proportion of its crystallisable sugar is converted into the uncrystallisable variety which passes away in the form of molasses and treacle. Another important cause of loss is the retention of a large amount of juice by the cane.
The following figures will convey an idea of the enormous quantities of cane sugar produced and consumed yearly throughout the globe. It is taken from ‘British Manufacturing Industries,’ one of a series of excellent industrial manuals published by Mr Sandford, of Charing Cross:
—
| Cuba | 600,000 | tons. |
| The other West Indian colonies | 250,000 | ” |
| Java and Sumatra | 170,000 | ” |
| China | 140,000 | ” |
| French colonies in America and Africa | 120,000 | ” |
| Brazil | 100,000 | ” |
| Mauritius | 80,000 | ” |
| British Guiana | 80,000 | ” |
| Porto Rico | 90,000 | ” |
| Manilla | 60,000 | ” |
| Mexico | 35,000 | ” |
| Egypt | Large and growing. |
The late Dr Edward Smith found that 98 per cent. of indoor operatives partook of 71⁄2 oz. of sugar per adult weekly; that 96 per cent. of Scotch labourers use it; and 80 per cent. of Irish. He further states that in Wales sugar is commonly used to an average extent of 6 oz. per adult weekly; but that there is a marked difference in the rate of consumption in the northern and southern portions of the principality. In North Wales, for example, the average amount per head is 111⁄4 oz.; whereas in South Wales it is only 3 oz.
The manufacture of sugar is exclusively conducted on the large scale. The recent canes are crushed between rollers, and the expressed juice is suffered to flow into a suitable vessel, where it is slowly heated to nearly the boiling-point, to coagulate albuminous matter. The crushed canes generally supply the fuel needed for this purpose. The ashes left after the combustion of the canes are carefully collected and used as a manure for future crops of sugar cane.
The cut below represents a press for the extraction of the juice from the canes. By means of the screws (i i), the rollers are adjusted to the proper distance apart; the upper
roller is half the size of the two lower ones, and all are moved by cogged wheels fitting on to the axes of the rollers. The sugar-canes are transferred from the slate gutter (d d) to the rollers (a c), which press them a little; and from thence they are carried over the arched plate (n) to the rollers (c b). The pressed sugar-canes fall over the gutter (f), the expressed juice collecting in g g, and running off through h. A small quantity of milk of lime is then added to the juice to remove mechanical impurities, and the skimmed and clarified juice, after being sufficiently concentrated by rapid evaporation in open pans, is transferred to coolers, and thence into upright casks perforated at the bottom, and so placed that the syrup, or uncrystallisable portion, may drain off into a tank or cistern from the newly formed sugar. During the period of crystallisation it is frequently agitated, in order to hasten the change, and to prevent the formation of large crystals. The solid portion of the product forms moist, raw, or muscovado sugar; the uncrystallisable syrup, molasses or treacle.[202]
[202] The term ‘molasses’ is usually restricted to the drainings from raw sugar, and ‘treacle’ to the thicker syrup which has drained from refined sugar in the moulds.