The molasses proceeding from the West Indian cane sugar contains crystallizable and unerystal lizable sugar, gluten, or albumen, and other organic matters which have escaped separation during the process of defecation and evaporation, together with saline matters and water. It therefore contains in itself all the elements necessary for fermentation, i. e. sugar, water, and gluten, which latter substance, acting the part of a ferment, speedily establishes the process under certain condi tions. Skimmings comprise the matters separated from the cane juice during tho processes of defecation and evaporation. The scum of the clarifiers, precipitators, and evaporators (see Sugar Manufacture), and the precipitates in both clarifiers and precipitators, together with a proportion of cane sugar mixed with the various scums and precipitates, and the " sweet liquor " resulting from the washing of the boiling-pans, &c., all become mixed together in the skimmings-receiver, and are fermented under the name of "skimmings." They also contain the elements necessary for fermentation, and accordingly they very rapidly pass into a state of fer mentation when left to themselves ; but, in consequence of the glutinous matters being in excess of the sugar, this latter is speedily decomposed, and the second, or acetous fermentation, commences very frequently before the first is far advanced. Dundee is the fermented wash after it has under gone distillation, by which it has been deprived of the alcohol it contained. To be good, it should be light, clear, and slightly bitter ; it should be quite free from acidity, and is always best when fresh. As it is discharged from the still, it runs into receivers placed on a lower level, from which it is pumped up when cool into the upper receivers, where it clarifies, and is then drawn down into the fermenting cisterns as required. Well-clarified dunder will keep for six weeks without any injury.
Good dundcr may bo considered to bo the liquor, or " wash," as it is termed, deprived by distillation of its alcohol, and lunch concentrated by the boiling it has been subjected to ; whereby the substances it contains, as gluten, gum, oils, &c., have become, from repeated boilings, so concentrated as to render the liquid mass a highly aromatic compound. In this state it contains at least two of the elements necessary for fermentation, so that, on the addition of the third, viz. sugar, that process speedily commences.
The first openttion is to elarify the mixture of molasses and skimmings previous to fermenting it. This is performed in a leaden receiver holding about 300 or 400 gallons. When the clarifica tion is complete, the clear liquor is run into the fermenting vet, and there mixed with 100 or 200 gallons of water (hot, if possible), and well stirred. The mixture is then left to ferment. The great object that the distIler has in view in conducting the fermentation is to obtain the largest possible amount of spirit that the sugar employed will yield, and to take care that the loss by evaporation or acetification is redueed to a minimum. In order to ensure this, the following course should be adopted. The ruom in which the process is carried on must be kept as cool as it is possible in a tropical climate; say, 24° to 27°. Supposing that the fermenting vat has a capacity
of 1000 gallons, the proportions of the different liquors run in would bo 200 gallons of well clarified skimmings, 50 gallons of molasses, and 100 gallons of elear dun der ; they should be well mixed together. Fermentation speedily sets in, and 50 more gallons of molasses are then to bo added, together with 200 gallons of water. When fermentation is thoroughly established, a further 400 gallons of duuder may be run in, and the whole well stirred up. Any scum thrown up during tho process is immediately skimmed off. Tho temperature of the muss rises gradually until about 4° or 5° above that of the room itself. Should it rise too high, tho next vat must bo set up with more duudcr and less water; if it keeps very low, and the action is sluggish, less must be used next time. No fermenting principle besides the gluten contained in the wash is required. '1'llu process usuully occupies eight or ten days, but it may last much longer. Sugar planters aro accustomed to expeet 1 gallon of proof rum for every gallon of molasses employed. Ou the supposi tion that ordinary molasses contains 65 parts of sugar, 32 parts of water, and 3 parts of organic matter and salts, and that, by careful fermentation and distillation, 33 parts of absolute alcohol may he obtained, we may then reckon upon 33 lb. of spirit, or about 4 gallons, which is a yield of about 5,1 gallons of rum, 30 per cent. over-proof, from 100 lb. of such molasses.
The operation of distilling is ofteu carried on in the apparatus represented in Fig. IM I. It is termed the Patent Simplified Diatiliing Apparatus ; it was originally invented 11 forty, but it has since undergouo much improvement. A is the body of the still, into which the wash is put; B, the head of the still ; ccc three copper plates fitted upon the upper part of the three boxes; these are kept cool by a supply of water from the pipe E, whieh is distributed by means of the pipes G G G. The least pure portion of the ascending vapours is condensed as it reaches tho lowest plate, and falls baek, and the next portion as it reaches the second plate, while the purest and lightest vapours pass over the goose-neck, and are condensed in the worm. The temperature of the plates is regulated by altering the flow of water by means of the cock F. For the purpose of cleaning tho apparatus, a jet of steam or water may be introduced at a. A gas apparatus is affixed at tho screw joint II, at tho lower end of the worm, which addition is considered au important part of the improvement. Tho part of the apparatus marked I becomes filled soon after the operation has commenced : the end of the other pipe K is immersed in water in the vessel L. Tho advantage claimed for this apparatus is that the condensation proceeds in a partial vacuum, and that there is therefore a great saving in fuel. One of these stills, having a capaeity of 400 gallons, is said to work off four or five charges during a day of twelve hours, furnishing a spirit 35 per cent. over-proof.