Another is known as “phospho-gelose,” which is a combination of dicalcium phosphate Ca2H2(PO4)2 and infusorial silica. It is a patented preparation and is made by the absorption of phosphoric acid by a powdery compound known as “Kieselguhr.” After the absorption, the compound is heated to expel the water, and then re-saturated. This work is repeated several times until the finished product, which is very hydroscopic, contains about 25 per cent of phosphoric acid.
Kieselguhr.—This is a fine light powder containing a high percentage of silica. It is used purely for its mechanical effect in forming particles upon which the impurities may collect, and thus be more readily carried to the bottom. This material often prolongs the workings of the filter presses by collecting the gummy material, which would otherwise gather on the filter cloths. Kieselguhr was used in the beet-sugar industry of Europe many years ago, and is extensively used now for the same purpose in the United States.
Hydrosulphites.—These are preparations of great bleaching power, found on the market under various trade names. One of these, widely used in the United States, in both the beet and cane-sugar industries, is known as “Blankit.” This is dehydrated sodium hydrosulphite with the chemical formula, Na2S2O4. It has a much greater bleaching and reducing action than sulphurous acid, and oxydizes very readily in combination with moisture, forming sulphate. On this account it is well to purchase the reagent in small parcels for this climate, and to carefully guard the stored material from moisture. This substance, which is a white powder, dissolves very easily in water, forming an alkaline liquid, although this point is sometimes hard to distinguish on account of hydrogen atoms liberated.
There is a bleaching preparation made in France known as “Redo,” which is simply calcium hydrosulphite (CaS2O4). This is used in the sugar industry to some extent, but it is claimed by many that the results obtained are not as good as those obtained from the sodium compound and that it deteriorates more easily.
Hydrosulphites, unlike sulphurous acid, will bleach equally as well in alkaline or neutral medium, as in an acid medium. There is therefore less danger from loss of sugar by inversion when they are used, while the permanency of their effect is about the same. In any case where juices have been bleached by sulphites, the result may be considered as but temporary, since upon exposure to air and light the product assumes a darker color. Hydrosulphites should therefore be introduced as late in the process as possible. Where the material in the vacuum pan is to be bleached, it is well to introduce this reagent just before striking grain, thus furnishing a bright clear material which will act as film over the nucleous of sucrose in the grain.
The chemical equation representing the change which takes place with this reagent is as follows:
Na2S2O4 (sodium hydrosulphite) + O (oxygen) + H2O (water)—>2(Na H S O3).
The amount to be used will depend absolutely upon individual conditions, which may be ascertained only by experimentation. The manufacturers of this product state that the amount of the material used to that of dry sugar should be as 1 is to 10,000. In the writer’s experience, two or even three times this amount will usually be required to give maximum results. As stated before, since there is such a variance in the material to be treated, each operator will be required to judge this to a great extent from the condition of his product.
In these Islands where a very low grade of open-kettle sugar is still made, which sells very cheaply, attempts are often made to bleach it and re-crystalize in order to make a centrifugal sugar.
While ordinary clarifying agents help to a great extent, if the melted sugars are very dark from caramel and the decomposition products of calcium glucosate, these reagents can not be expected to give a light-colored juice. While they may improve conditions somewhat, the only solution to such a problem is the use of the boneblack process.