Improvements in sugar manufacture

In the early part of the year 1849, I had formed an intimate acquaintance with a Mr. Cromartie, a Jamaica sugar-planter, and at many of our friendly meetings we had discussed the question of the sugar manufacture as then carried on in the West Indian Islands. The more I heard of the state of this important industry, the more astonished I became on finding out how rude, how unmechanical, and how unscientific were many of the processes then employed, not only in extracting the saccharine juices of the cane, but also in its after-treatment. By a curious coincidence, at this very period the imperfection of the Colonial sugar manufacture had attracted the attention of the Society of Arts, and his Royal Highness Prince Albert had taken a very special interest in this subject, and generously offered a gold medal to be awarded to the person who should, during the ensuing year, effect the greatest improvement in the mode of expressing the saccharine juice of the sugar cane. I was much interested on hearing this, and applied myself to the problem with great zest, for I heard that the contest was to be an unusually sharp one. I was informed that the manufacturers of Colonial sugar machinery looked on it as a question that would decide which firm was in future to do the bulk of the Colonial engineering work, and that powerful vested interests were supposed to be at stake. This rendered it the more necessary that I should make every effort to gain such a knowledge of the subject as would enable me to devise a machine capable of extracting, as completely as possible, the whole of the juice from the cane. I, therefore, in the first place, obtained from Madeira a bundle of sugar canes, and I may say that up to that time I had never seen a cane. Those I had ordered to be sent to London arrived fresh and full of juice, as I had directed that their ends should be dipped in melted pitch, so as to prevent decay, and the escape of any juice from them.

These canes were from 1 1/2 in. to 1 3/4 in. in diameter, having dividing knots at from 5 in. to 7 in. apart, throughout their length. The cane consists of an outer tubular part of hard fibrous wood, thinly coated with very hard pure silica; the interior of the thin wooden tube is filled with a soft pithy matter, almost like a sponge, saturated with juice, of which the ripe mature cane contains about 88 to 90 per cent. of its whole weight. I put short lengths of these canes to many tests in different ways, and especially noted their great elasticity; a 6-in. length, suddenly pressed between two flat surfaces, would lie in a complete pool of juice, and if the pressure were quickly released, the flattened elastic tube would again expand and as quickly reabsorb a very large portion of the fluid with which it was in contact. Here, I saw at a glance, was the weak point in the roller-mill, in which the cane quickly enters between a pair of rolls, and is for the moment collapsed. But as it emerges from them it again expands by its elasticity, drawing into the expanding spongy mass a large portion of the juice, which is rapidly flowing in contact with it, over the lower roll of the mill. This will be readily understood by reference to the engraving, Fig. 17, page 87, showing in section a pair of iron rolls A, A, between which a cane B is passing in the direction shown by arrows. It will be observed that at the central part the cane is crushed very thin; but as it emerges, it, in part, recovers its former dimensions, and in doing so absorbs a very large percentage of the juice previously expressed.

These and other observations, carefully made and noted at the time, forced on my mind the conviction that no form of roller-mill could, from the inherent nature of its action, give satisfactory results; and that a slower and longer continued pressure on the cane must be resorted to, if the greater part of this valuable fluid was to be extracted.

By means of the hydraulic press, 86 per cent. of juice could be obtained; but this system was far too slow, and entailed so much labour as to render it impossible to deal with the enormous mass of canes grown on a moderate-sized plantation. Following, however, the general idea of the press, I designed an entirely novel system of extracting juice from canes, the main feature of which was the cutting of the cane into lengths of about 6 in., thus leaving both ends of these short pieces open for the escape of the juice, instead of operating in the usual way upon canes of 4 ft. to 6 ft. in length, having numerous transverse knots or partitions, which effectually prevented any escape of the juice endwise. The two convex surfaces of a pair of rolls of 2 ft. in diameter, pressed on less than 6 in. of cane, at any moment, and if they revolved as slowly as five revolutions per minute, the 6 in. of cane passing between them