3. "To complete the concentration in a vacuum pan, or by other means, at a moderate temperature, not hurtful to the sugar, and facilitate the natural process of crystallisation, so as to obtain sugar of a large and distinct grain."
4. "To drain and dry the sugar perfectly, and to save all the molasses."
The advantages to be anticipated from these improvements, superadded to an improvement in cultivation, cannot be estimated at less, upon a moderate calculation, than from 150 to 200 per cent. of increase in the production of sugar, with hardly an appreciable increase of labor or expense; for we have, in the first place, a gain by improved culture of, at least, two hogsheads an acre in sugar, equivalent to 100 per cent.; in the next, by employing improved mills and extracting the residuum, 30 per cent.; by conducting the process of manufacture more judiciously, 10 per cent.; and by the prevention of waste during the transit to market, 10 per cent., making a total of at least 150 per cent.
The common sugar-mill consists of three cylinders, tightened either by wedges, if in a wooden frame, or by screws in a cast-iron frame. If in an iron frame, the above-mentioned noise is obviated, but the friction and loss of power is the same, which is ascertainable by subsequent investigation. The cylinders or rollers, which are moving either horizontally or vertically, are from eighteen to twenty-four inches in diameter, with bearings or shafts of one fourth of their diameter. If the bearings or shafts of the cylinders were of less substance, they could not resist the great strain to which they are subjected when in operation. The whole of the prime mover (steam-engine, water-wheel, or animals), minus the friction of intermediate machinery, is transmitted to the plains of these rollers and resisted by their bearings; hence the action is equal to a weight moving on low wheels of eighteen or twenty-four inches in diameter, on axles of from four to six inches thickness, which weight is equal to the force applied; consequently, if the strain is greater than the resistance of the rollers or the bearings, they must be wrenched off, or if greater than the force applied, the mill will be stopped. The power necessary to move weights upon wheels, on a smooth and level surface, is in proportion to the respective diameters of wheels and axles. The same pull which moves one ton at a given velocity upon a wheel of two feet, with an axle of six inches, will move four tons, if on a wheel of four feet diameter, with an axle of six inches. Consequently, cylinders of small diameter, with strong and substantial bearings, are only admissible as working machines, if no other mechanical means are applicable, as, for instance, in rolling out metals, compressing the surface of various bodies for a glossy appearance, or, generally speaking, to produce a certain and equal form of the substance which is pressed and passed between them. They compress the atoms of bodies, and for this reason alone are ill suited to separate the fibres of the sugar canes, and to express effectively the saccharine matter between them. A practical proof of this demonstration is furnished by every sugar cane which has gone through the mill. Fresh megass is at present better suited for fattening animals than for fuel under the sugar pans.
The loss of material thus sustained, which is, on an average, equal in every mill, whether driven by steam, water, or animal power, is entirely chargeable to the construction of the mill, and amounts to about ten per cent. of the saccharine matter contained in the sugar canes.
M. Duprez, an agent of the French Government, having experimented on the canes in Guadaloupe, found the quantity of juice in every 100 lbs. crushed—
| lbs. | |
| 1 By mills having horizontal rollers; the motive power not stated | 61.2 |
| 2 By mills, motive power, steam | 60.9 |
| 3 By mills, motive power, wind and steam | 59.3 |
| 4 By mills, having vertical rollers | 59.2 |
| 5 By mills, motive power, cattle | 58.5 |
| 6 By mills, motive power, wind * | 56.4 |
| [* Dr. Evans' "Treatise on Sugar," p. 75.] |
The average of all these experiments being 56 per cent. only. The result of M. Avequin, on Louisiana cane, was 50 per cent. Mr. Thompson, of Jamaica, states 50 per cent. as the average throughout the island of Martinique. Dr. Evans ventures 47 per cent. as the lowest, and 61 per cent. as the highest in the West Indies. A mill in Madeira gave 47.5 and 70.2 of juice—the larger yield being obtained by bracing the horizontal rollers more than usually tight, and introducing only a few canes at a time, the motive power being cattle.
The three roller mill has the disadvantage of re-absorbing a part of the cane juice in the spongy megass, (or trash as it is termed in the West Indies), and a loss of power.
Those with five rollers have been used in Cuba, Bourbon and the Mauritius, which gave 70 per cent., but a great increase of motive power is necessary. Four roller mills, two below and two above, requiring little more motive power than three rollers, have given 70 to 75 per cent of juice.