Phosphoric acid.--It is sometimes advisable to apply a form of phosphoric acid as a clarifying and precipitating agent after the lime. This may be used in various forms depending upon the individual desires of the operator. The compound usually found on the market may consist of one of the following (or a combination of them): H3PO4 (ortho phosphoric acid). CaH4(PO4)2 (mono-calcium phosphate). Ca2H2(PO4)2 (dicalcium phosphate). Na2HPO4 (sodium phosphate). The sodium phosphate contains very little acidity, and the main purpose of its use is based on the principle that the sodium is readily given up for any soluble calcium that may be present. This forms the insoluble calcium phosphate, which is easily removed as a precipitate or filtered off. The "Reserve Factory" in Louisiana has been using this reagent in their clarification for a long time, where a very good grade of granulated sugar is made. Besides these forms of phosphorous, various compounds may be found on the market, under trade names, which have as their base the above acid. "Clariphos" is one of these compounds, which has found extensive use in many of the Louisiana sugar factories. 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 resaturated. 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.