Sulphurous acid.—Next came the separate introduction of the lime and the sulphurous acid into the juice. This system has grown into very wide use in the TJnited States, W. Indies, and other places. There are two principal ways of carrying it into effect :—(1) By first passing sulphurous acid gas into the juice, and then adding lime : known as Col. Stewart's process, patented in Louisiana and the W. Indies, and recently adopted in Egypt and elsewhere ; (2) by first adding the lime, and then passing the sulphurous acid gas : Beanes' system, chiefly employed in Cuba, but also in Java and Anstralia. The effect is probably identical in both cases. The first described plan is far the most common.
At Aba-el-Wakf, the following plan has been introduced. As fast as the raw-juice tank is filled, its contents are raised to the clarifiers, steam at 60 lb. being turned on as soon as the bottoms are covered. When the juice begins to boil, it is stirred with a copper pipe, through whose lower perforated end, sulphurous acid gas is injected, and allowed to dissolve in the juice, till the colour of the latter becomes considerably lighter, and a decided separation of the flocculent matter takes place. The quantity of sulphurous acid to be added varies : approximately, 450 gal. would require the combustion of lb. of sulphur. The sulphurous acid is forced into the juice by an iron pump (with indiarubber flap-valves), whose speed can be adjusted to the quantity required. The gas is generated by the combustion of crude sulphur in a cast-iron D-shaped muffle, tbe necessary air being sucked through by the pump; as the combustion depends on the air-supply, and the latter on the speed of the pump, the whole apparatus is self-adjusting. Some 50-60 ft. of 3-in. cast-iron cooling-pipe, with numerous holes for removing " flowers " as formed, conduct the gas to the tanks.
As soon as the boiling juice is sufficiently " gased," milk of lime mixed with China-clay is added at the rate of i-3 gal. per 450 gal. of juice, till it is perfectly neutral ; it is then let into subsiders to stand till the impurities have settled. The use of sulphurous acid necessitates the employment of about 4 per cent. additional lime. The combination of sulphurous acid and lime permits the production of a grey-white muscovado (" grocery ") sugar.
Other Alkaline Earths.—It has been proposed to replace lime in defecation by other alkaline earths, such as barium and strontium. Their effect is more powerful than that of lime, but they have not come into general use on account of the prejudice regarding their poisonous qualities, and the risk of some being left suspended in the sugar. As regards barium, there is no proof of its
deleterious qualities when present in such quantities as are found in sugar treated with it ; but an expert can at once detect the use of any barium salt, by the modified form of the sugar-crystals, which modification shows that barium salts are still present, and hinders the sale of such products.
Lime sucrate.—This process is described under Refining.' Lead acetate.—Many ye,ars ago Dr. Scaffern employed the subacetate of lead (" sugar of lead ") as a defecating agent, and many inventors have since improved on his method of manipula, tion. This c,arries down many of the impurities as a precipitate, leaving sugar in solution, and any possible excess of the lead salt is thrown down as insoluble sulphite by the injection of sulphurous add. Sugar was prepared by this process, without any injury resulting, but an outcry against the poisonous nature of lead acetate, and the dread that some rnight be accidentally left in the sugar, caused the process to be officially condemned. Lead certainly was present in the sugar, but it is not known whether it was in a poisonous form or not.
Snlphur and Chlorine compounds.—One of the most recent innovations in defecating fa the invention of Eastes, Lukin, and Boyd, of Brisbane, and known as " Eastes' process." The juice may be tempered and clarified either hot or cold, but the liquor must be heated to boiling point to coagulate all the albumen. When the juice is in the clarifier, 4-8 oz. of chloride of sulphur are added to each 100 gal. of juice, according' to the supposed quantity of albuminous matter present, the necessary quantity first beiug mixed thoroughly with a small quantity of the juice in a small vessel, and then gradually poured into the clarifier, whilst the liquor is agitated. In addition to the chloride of sulphur, in the case of juice containing free acid, sufficient lime must be used to neutralize it. Sulphide of lime and " cbloralum " (chloride of aluminium) may replace the chloride of sulphur. After the application of the particular chemical selected, the liquor is brought to boiling-point, and allowed to rest for not less than 45 minutes, by which time the precipitate will subside, and a perfectly clear liquor remain. This is then run off to be evaporated.