At Valenciennes I met with Mr. Cail, who, beside being an engineer and machine-maker, is interested in sugar-making, both in France and in the West Indies, and most thoroughly understands the subject. He invited me to accompany him to Douai, to see a new set of works which had been set agoing this month. I was of course too glad to accept his invitation, and started with him at six next morning, reached Douai at eight, and then proceeded to the works, which are a few miles out of town. In this work a new process is also employed; it is that of Mr. Rouseau, and is said to answer well. The beet root juice, as soon as possible after expression, is thrown up by a montjus into copper clarifiers with double bottoms, heated by steam at a pressure of five atmospheres. To every hundred litres of juice (=22 gals.) two kilogrammes of lime are added (about four and a half pounds English weight). The lime is most carefully prepared and mixed with large quantities of hot water till it forms a milk perfectly free from lumps. The steam is turned off, and the juice heated to 90 deg. A complete defecation has taken place, the steam is shut off, and the juice left a short time, to allow the heavier impurities to subside. It is then run off in the usual manner, undergoes a slight filtration through a cotton cloth placed over a layer of about four inches thick of animal charcoal, and runs into a second set of copper vessels placed on a lower level than the clarifiers; these vessels are heated by means of a coil of steam piping sufficient to make them boil. A second pipe passes into them, making a single turn at the bottom of the vessel; this is pierced on the lower side with small holes, through which a stream of carbonic acid gas is forced.
This decomposes the saccharate of lime, which has been formed in consequence of the large excess of lime added to the clarifiers.
The lime is precipitated as carbonate. When precipitation has ceased, steam is turned on, and the whole made to boil; this expels any excess of carbonic acid; the liquor is then run off, undergoes a similar partial filtration to that mentioned above, and is then passed through the charcoal filters to be decomposed. The sugar made by this process, directly from the beet-root juice, is nearly white. The molasses is re-boiled as often as six times; each time undergoing a clarification and filtration through animal charcoal. And the proceeds of the last re-boiling is certainly in appearance not worse than a great deal of muscovado I have seen shipped from Trinidad.
In this work there are about 150 people employed. The work goes on night and day, one gang replacing the other. The whole evaporation is done by two vacuum pans, each 6½ feet in diameter, 80,000 kilogrammes of beet-root are used daily, from which about 6,000 kilogrammes of sugar are obtained, equal to about 6 tons English weight.
In these and every other works I visited—eight in all—the centrifugal machines were in use, and had in most cases been so for two years; those lately made have been much simplified in construction, and work admirably. Cail & Co., of Paris, are the makers; their charge is 3,000 francs for each machine (£120 stg.). They require about one and a half horse power each. As they are wrought in France, one machine is about equal to work off a ton and a half of sugar daily, working all the 24 hours. Mr. Cail recommends a separate engine for those machines; so that they can be used at any time, independent of the other machinery. The charge put into a machine is about 80 kilogrammes, from which about 30 to 35 kilogrammes of dry sugar is obtained; the calculation is, I believe, 40 per cent. I weighed some of the baskets of sugar taken out after drying, and found them 35 kilogrammes. Sugar intended for the machine is never concentrated beyond 41 degrees Baumè; that made from the juice direct is allowed 18 to 34 hours to crystallize, and is put into the machine in a semi-liquid state; the motion at first is comparatively slow; in about three minutes the sugar appears nearly dry; about three-fourths of a gallon of brown syrup is then poured into the machine whilst in motion, and the speed brought up to its highest, about 1200 revolutions a minute; in 3 or 4 minutes more the machine is stopped, the sugar scooped out and thrown into baskets, the inside of the revolving part, and especially the wire cloth, carefully washed with a brush and water, and a fresh charge put in. The whole time betwixt each charge is about 15 minutes. From the large proportion of molasses you will see very plainly that those who do not intend to re-boil, need not think of centrifugal machines. The sugar dried in this way is not altogether white, but has a slight greyish yellow tinge.
Of the other sugar works which I visited, the only one of peculiar interest was that of Mr. Dequesne, near Valenciennes. Here the roots are first cut into small pieces by an instrument similar to a turnip slicer, then dried in a species of kiln, and stored up till required. In this way I was told beet-root could be preserved with very little deterioration for a full year, and this enables Mr. Dequesne to go on making sugar all the year round. When the sugar is to be extracted, the dried cuttings are put into a series of closed vessels connected by pipes, and by a system of continuous filtration of warm water through these vessels the solution of sugar is obtained, of a density equal, I believe, to 25 degrees Baumè; it is a good deal colored, and requires filtration through animal charcoal. Mr. Dequesne informed me that for five years he had been unable to make this mode of sugar-making cover its expenses, owing to the loss occasioned by fermentation taking place in the beet-root; but that he has now entirely overcome that difficulty; by what means I was not told.
The number of macerating vessels is fourteen, ten of which are working at a time, the other four filling and emptying.
A greater number of vessels, Mr. Dequesne thinks, would be advantageous, as cold instead of hot water could then be employed. He thinks a similar plan might be introduced in the West Indies with great advantage, and that by employing the proper means to prevent fermentation the sun's heat would be quite sufficient to dry the cane slices.
Mr. Dubranfaut and Mr. Rouseau's processes are patented in England. The terms for the use of the former would, I was told, be made so moderate, as to offer no obstruction to its being used in the colonies. What Mr. Rouseau's terms are I could not learn.
There are now 288 works making beet root sugar in France, and over 30 in Belgium. The same manufacture is rapidly spreading in Germany and Russia, and is now being introduced in Italy. Whilst at Valenciennes, I learned that two English gentlemen had just preceded me in visiting the works in that neighbourhood, mentioning that they had in view introducing the beet root sugar manufacture in Ireland.