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Previous Next The best candle and soap tips online! MATERIALS USED IN THE MANUFACTURE OP SOiPS 55 Chemical analysis demonstrates that 100 parts of crmlt artificial soda contain on an average:— 20 to 25 30 to 35 2 to 5 1 to 2 Pure soda . Salt U11 decomposed sulphate of soda Foreign salts . The insoluble residuum is composed of oxysulphuret of lime, and coal. Jifjiiud Carbonate of Snila.—Purified carbonate of soda is designated in the tiado by the name of soda ash. This salt is very important on account of ita numerous applications in industry. It is specially used in the preparation of toilet soaps. For their fabrication the richest in alkali is preferred, nnrt principally the one which is entirely free from sulphuret. For a long time this salt was obtained by the lixiviation of the ashes of sea-weeds, bat now it is extracted from artificial crude soda. To prepare this salt, select the soda which is richest in alkali, and containing-the least sulpha ret. The lixiviation may be efleoted by various processes. Iu the manufacture of crude soda, where sal soda is also prepared, the process is rational, simple, and economical. Baskets made of metallic eioth arc filled with coarsely powdered soda, and then successively passed through solutions of soda growing weaker and weaker. The last passage is through pure water. By this operation a solution at 25° or 28° B. ia obtained. To have it perfee:ly limpid, it is left to settle for several days, and is then concentrated. This operation is generally conducted in four cast-iron kettles arranged in steps, and heated by the same hearth. The first receives the heat directly all over ita surface; the flame afterwards heats the others, and then is lost in the chimney. The top kettle is employed to boil the solutions, the middle ones to evaporate them, and the lower one to eoncentra;e them to drynese. During the operation, add new solutions to take the place of the evaporated water, in such a manner that the level of the liquors is always the same. To prevent the salt from attaching itself to the bottom aud the sides of the first kettle, take it out with a skimmer as fast as it deposits, and let it drain on an inclined plane, or on. shelves lined with lead. Continue this until all the solutions are evaporated to dry ness. To obtain a very pure and very rich carbonate of soda, Borne manufacturers evaporate the solution until a pellicle is formed on the surface, and in this state pour it into sheet-iron vats, where it crystallizes. A few days after, the mother-liquor is decanted, and the salt is left to drain. The crystals contain only a few hundreths of foreign salts; the mother-liquor contains uncrystallizable caustic soda, sulphate of soda, and chloride of sodium. Whatever be ths method of operating, the salt of soda obtained always contains a large amount of water, interposed between ita crystals. Besides, it is colored by organic substances, which give it a brownish shade. To obtain this salt very dry and very white, calcine it in a reverberatory furnace, strongly heated. Furnaces iu which the calcination takes place have their beds entirely covered with a thick and half-melted coat of salt itself; the bricks or stones being rapidly destroyed under the influence of a high temperature. The carbonate of soda thus obtained is very white, and is much richer in pure soda when the crude soda, from which it is exhausted, is itself pure. The sal soda is obtained nearly chemically pure, as we have said, by concentrating the solutions of crude soda and causing them to crystallize. Tlie crystals being drained and calcined in a reverberatory furnace, yield a carbonate of soda of 90 or 92 alkalimetrie degrees. The amount of refined soda ash from crude soda, varies according to the quality of the soda used. Generally, 1000 pounds of good crude soda, at 36°, yield from 383 to 400 pounds of a very white refined soda ash, and marking from, 80 to 85 alkalimetrie degrees. Crystallized Carbonate of Soda or Crystals TECHNICAL TREATISE ON SOAPS AND CANDLES. MATERIALS USED IN THE MANUFACTURE OP SOAPS. 57 merous applications ID the arts. In soap factories it is used to prepare the pure lye of soda. Nearly all the crystallized sal soda found in commerce is obtained by the iisivisition of artificial soda. To prepare it use the purest and richest, soda. The <:rude soda is lixiviated in the same manner as we have indicated above. All the solutions which mark from 20° to 25° B., are mixed in large sheet-iron vats and allowed to rest; a few days after, when all the liquors are clear, they are decanted and submitted to a gentle ebullition in a cast-iron kettle. When the boiling solutions mark from 28° to 30°, they are poured back into the vats, which are surrounded with coarse cloths, so as to retard the cooling. By resting, a sediment is deposited at the bottom of the kettles, and the liquor becomes perfectly limpid. Wlien the temperature is at 70° to 75D C. (158° to 167° F.), the liquors are decanted and then set to crystallize, either in earthen jara, or in small sheet-iron vats of a, capacity of 6 or 8 gallons. In winter, the crystallization takes place in the space of a few days. When the concentration of the lyes has been carried to 34° or 35° B., the crystallization is PO complete that very little niothei-liquor is left. The concentrated lyes at 26° to 30°. give less crystals, but the product is richer. The caustic soda and the foreign salts remain in solution in the mother-liquor, while in the first case, they crystallize with the carbonate of soda. Another process is also used to prepare the crystals of soda. It consists in dissolving retined soda ash, of a high degree, in boiling water. The operation is effected in a cast-iron kettle. When the liquor marks 30° E., T^TC °f quicklime, diluted with water, is added to it. After au ebullition of a few minutes the fire is removed, and the liquor is allowed to rest, so as to become limpid. This result being obtained, the clear liquid is drawn off and left to crystallize. The crystallization takes place in a few days; the salt is then separated from the mother-liquor and allowed to drain. This process yields whiter, finer, and purer crystals than those obtained by the direct treatment of the crude soda.
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