Fig. 185 represents a double still which is largely employed in the colonies. It is simply an addition of the common still A to the patent still B. From time to time the contents of B are run off into A, those of A being drawn off as dunder, the spirit from A passing over into B. Both stills are heated by the same fire ; and it is said that much flue spirit can be obtained by their use at the expense of a very inconsider able amount of fuel. In Jamaica, however, nothing is likely to supersede the common still and double retorts, shown in Fig. 186. It is usually the custom to pass the tube from the second retort through a charger containing wash, by which means the latter is heated previous to being in troduced into the still ; the tube then proceeds directly to the worm-tank. With an arrange ment of this kind, a still hold ing 1000 gallons should produce 500 gallons of rum (30 to 40 per eent. over-proof), between the hours of five in the morning and eight in the evening. The first gallon of spirit obtained is termed "low wines," and is used for charging the retorts, each of which contains 15 to 20 gallons. After this, rum of 40 to 45 per cent. over-proof flows into clean cans or other vessels placed to receive it.
ALconor, FROM GRAIN.—The different cereals con stitute a very important source of alcohol in this country and also in Belgium, Holland, Germany, and America. The spirit obtained from them is termed " grain spirit ;" large quantities of that dis tilled in England are sent to London for the prepara tion of gin, the remainder going to the Scotch and Irish whiskey distilleries. The cereals contain an amylaceous or starchy substance, which, under the influenco of diastase, is converted into fermenteseible sugar. The quantity of sugar, and conse quently the yield of alcohol, produced from each variety differs widely. The following table shows the results which may be obtained from good workmanship :— From this it will he seen that rice, wheat, rye, and maize are more frequently employed than the rest ; barley and buckwheat are added to these in some proportions. Oats, owing to their high price, are rarely used, except for the purpose of giving an aroma to the alcoholic products of the other grains. Some care is requisite in making choice of the grains for fermentation. The wheat selected should be farinaceous, heavy, and dry. The barley should be free from chaff, quite fresh, and in fine large grains of bright colour. Rice, which of all grains is the most productive to the distiller, should be dull white, slightly transparent, without odour, and of a fresh farinaceous taste ; the rice of commerce is chiefly supplied from the East Indies, Piedmont, and the United States.
The flour, or farinaceous part of grain, is composed essentially of starch, gluten, albumen, mucilage, a little sugar, and traces of inorganic salts.
Under certain conditions, the albumen or gluten contained in the grain has the power of converting starch into sac,charine matter ; this change is, however, better effected by a mineral acid, by germinated barley, or by diastase. This latter substance is a principle developed during the
germination of all cereals, especially uf barley. It has the nmarkable property of rateting upon starchy nuater8, converting them, first, into a gummy substance, called dextrine, and then into glucose, or grape sugar. This principle does not exist in the grain before germination. Its action upon starch or flour made into a paste is very remarkable; 50 grains of diastase are sufficient to convert 100 kilos. of stareh into glucose. The rapidity with which the change is effected depends main thc quantity of wator employed, and the degree of heat adapted to the opemtion. Diastase is generally prepared from barley, as this grain germinates more readily and develops a larger pro portion than any other.
There are six processes to which the grain must be subjected before it is ready for fermentation. They are—(1) Steeping, (2) Germination, (3) Drying the malt, (4) Grinding, (5) Mashing, and (6) Infusion. Wo shall briefly notice each of these operations.
Steeping.—This operation, which requires much attention, is conducted in a wooden vat, or stone tank, lined with hydraulic cement. The grain is placed in the tank and covered with river or NN ell water for a space of 30 or 40 hours, according to the temperature of tbe atmosphere, the quality or dryness of the grain, and the character of the water. In very warm weather, the water should be changed every four or six hours, by running it out through a hole in the bottom of the vat, and running in fresh at the top ; this is done in order to prevent fermentation from setting in prematurely. Whorl the grain swells, and yields readily when crushed between the fingers, it has boen sufficiently steeped, and the water is run off finally% Germination.—After the water has run off, tho grain is allowed to drain for a few hours, and is then conveyed to the malt-house. This is kept constantly at a temperature of 12', and is always paved with stone. Here the grain is arranged in beds of two or three feet in thickness, until it becomes sensibly heated. Soine hours after these beds have been prepared, vital movement commences in the grain, atteuded• by a considerable elevation in temperature, which increases gradually until it is about 7° or 8° higher than that of the room itself. During this time tho grain absorbs oxygen, and gives out carbonic acid a ith much rapidity. ; it also becoraes moist, and gives out a peculiar, somewhat agreeable, odour. The gmiu must not be allowed to become tou warm, and should be turned over every six or eight hours, until germination begins, and then every three, four, or flve hours, according to the temperature ; this should always be maintaiued at about 15° ur 16°. The whole process occupies from eight to fifteen days, according to the season ; it is over when the little roots have attained a length equal to about two-thirds ot that of the grain.