McDowell's concentrator, Fig. 1388, differs in having a closed top and a water-jet condenser, producing a vacuum. In this, 600 gal. of evaporator-juice are reduced to 200. The product is then " semi-syrup," and can be stored, or shipped to a refinery, or further reduced in a vacuum-pan.
Fig. 1389 is a direct steam evaporator, which boils clarified juice by means of a steam-coil, the scum passing over into the trough around the upper edge.
Fig. 1390 is a steam-train, made at the Colwell Iron Works, New York. It consists of 3 clarifiers, and an evaporator, requires little labour, dispenses with pumps and ladles, and finishes the syrup up to the vacuum-pau.
Fig. 1391 is a cheap home-made evaporator, which can be put together by an ordinary mechanic. It is con structed by putting wooden sides and ends upon a galvanized iron or copper tray.
Fig. 1392 shows Stubb's evaporator. The first compartment occupies of the whole pan, leaving for the second. The juice enters the first compartment uear the smoke-stack in a. regular stream, passing arbund the semi-eirele over the fire-box to cross-partitions, where it thickens to a semi-syrup. Being over the hottest part of the furnace, it rises to a light foam, which breaks to the lowest p-oint where the cool juice enters, not only keeping back the green scum, but carrying all the scum off 30 ft. of surface, where it is scraped off without loss of sugar.
The semi-syrup is turned into the second compartment at intervals, to be finished under full control of heat governed by dampers.
Defecators.—Fig. 1393 is McDowell's defecating-tank, 8 ft. long, 5 ft. wide, and 2 ft. deep. The bottom is covered with a steam - coil, and contains a strainer, through which the clear juice can be drawn. Each tankful can be treated in 30 minutes. Two of these tanks suffice to defecate 600 gal. per hour.
Fig. 1394 represents the apparatus required in F. L. Stewart's process : a defecating-tank D, a short 10-gal. cask C, a lacquered funnel F with indiarubber ring around the neck, a plug r for thrusting into the throat of P, and a piece of indiarubber piping R. Directions for its use are as follows :—Place the cask on a bench nearly level with D. Pour 1. gal. of water into the cask, then pour gal. sulphuric acid into a wooden bucket, allow it to flow thence into the cask, and well mix it. Next insert the rubber-covered neck of the funnel tightly into the larger hole in the head of the cask. Compress one end of the long tube slightly, and imert it in the smaller hole. Insert the plug with the rubber ring around it in the throat of the funnel closely, and it moll be air-tight. This is then ready to work, as indicated.in section 6.
Some of Stewart's patent powder is dropped quickly, 1 lb. at time, through the funnel into the cask containing the diluted acid, the plug is quickly inserted, and immediately sul phurous oxide escapes through the tube into the clear juice in the tank D ; 1 lb. of powder is usually sufficient for 150 gal. of juice when its gas is all discharged. The juice must absorb the gas until it becomes acid. Never allow the cask to get more than half-full of the mixture, or the sulphuric acid may foam over into the juice and decompose some of the sugar. Lift the end of the rubber tube out of the tank when the gas ceases to flow, or the juice may be forced back into the cask. In factories where 1000 gal. of juice are run into the defecating tank at once, a 40- or 50-gal. cask should be used. The sulphuric acid is neutralized when about an equal weight of tho powder has been dropped in ; therefore 1 gal. of acid poured into 2 gal. of water will eliminate the gas from about .14i lb. of the powder. When this proportion hes been reached, or when the gas ceases to flow upon the addition of more powder, empty the contents of the cask, preserving the fine sediment for use as a fertilizer : it is principally sulphate of lime. Rinse out the cask, and go on as before.
The complete operations are :—(1) Heat the freshly-expressed juice in a copper or tinned-iron vessel to 82° (180° F.) ; (2) stir in gradually milk of lime until the red test-paper turns blue : about B pints to 100 gal. of juice is generally needed ; (3) heat rapidly to the boiling-point, and then shut off the heat, or remove theyessel from the fire ; (4) as soon ss the sediment begins to settle, siphon off the clear liquid from near the top into cooling- or defecating-tank, until at least ?„ of the juice has been removed, leaving a thick muddy sediment at the bottom ; (5) sweep ont this muddy sediment with a broom through a large opening at the bottom of the heater, into a smaller vessel below, and rack off any clear juice that afterwards separates from it, and add to the contents of the de fecating - tank ; (6) into each 150 gal. of this clear and partly cooled juice fn the defecating-tank D, in troduce as much gas as is produced by operating with 1 lb. of the powder, or until blue litmus-paper is reddened ; (7) the juice is run into the evaporator, and boiled rapidly in as shallow a bed as possible, removing any soum that forms : it shonld continue acid until the close of the boiling ; (8) before the syrup has become very dense, it is passed from the evaporator into the floishing-pan. Evaporate here rapidly to a denso syrup, stirring constantly at the last, when a white cloud begins to be seen in it at about 113° (235° F.); turn out into the cooler, snd remove to a warm place to crystallize ; when cooled to about 38° (100° F.), stir a few grains of sugar in to hasten it.
Coolers.—Fig. 1395 shows a very convenient arrange ment for cooling syrup.
Complete Factory.—Fig. 1396 illustrates the arrange ment of a complete sorghum sugar factory. The juice;after running from the crushing mill into a tank on a lower level, is pumped into the juice-tank a. b is the defecator ; c, settling-tanks ; d, supply-tank for evaporator e ; f, supply-tank for strike-pan g ; h, receptacles for scum ; i, trucks for conveying the syrup to the sugar-room. The cost of such a factory is about 2000/. for a small size.
Local Details.—In New South Wales, sorghum has been fouod to stand frost better than the eugar-cane proper, and is little affeoted by floods. It comes to maturity in 5 months, and therefore may be employed as an interval crop, altercating with sugar - cane, and keeping the sugar-mills going. In 1868, there were 296 acres planted with sorghum in various districts ; but in 1872, this was reduced to 32 acres. Growers expeot 1/-2 tons of sugar to the acre. When not grown for sugar, the plant yields abundance of valuable food for cattle, at the rate of 30-40 tons of cane per acre.
In France, Vilmorin states that it is capable of yielding on an average, from an acre of land, - 26,000 lb. of juice, containing 10-13 per cent. of sugar ; and that is more than the avemge yield of the sugar-beet. It is alleged, however, that the plant is adapted to only a few parts of S. France.
Wray asserts that some of the varieties which he introduced from Natal gave 30 cwt. of sugar per acre, and that it has yielded from a poor hand-mill 68 per cent. of juice, containing 15 per cent. of sugar. Where the sugar-cane has yielded 30 cwt., sorghum has given 25, but then there is often a second and a third crop to be obtained within the year. Sorghum can in many localities be advantageously utilized for preparing syrup. For this purpose, the juice is expressed at the time of flowering, and simply evaporated ; the yield is about 100 gal. per acre.