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Previous Next The best candle and soap tips online! TECHNICAL TREATISE ON SOAP AND CANDLES. THE FABRICATION OP SOAPS. 289 addition of about 5 per cent, cocoa oil is made; the soap thereby attaining the property of frothing very well. The rosin-grain soap is always produced with very caustic lye, which is best prepared by dissolving caustic soda in water. The rosin must be well pulverized, before it is placed in the kettle, and immediately well stirred, as the matter easily ascends and runs together into lumps, which can only be re-separated with difficulty. A preliminary boiling in this case is not necessary, though the lyes should be added in portions, the boiling being well sustained, care being taken to add weak lyes or water to make up for evaporation. When the soap has assumed the true gelatinous appearance, it can be separated from its, superfluous water with salt, and afterwards fitted or ground to bring it to the proper consistency. This is often done with a solution of carbonate of soda. OLEIN SOAP, OLEIC ACID SOAP, ELAIDIN SOAP. Under these various names is the soap made from oleic acid (commonly known as " red oil") called. This acid, being a by-product in the making of stearic acid, stearin, and glycerine by means of lime, sulphuric acid, etc., though it is limpid at ordinary temperatures, contains some stearin and palmitin, but no glycerine, and as it is generally low in cost, it makes an economical and useful soap, either by itself or in combination with other greases, as tallows, cotton-seed oil, rosin, etc. There are numerous modes of saponifying this valuable 8ebacic acid, and it is difficult to say which produces the best soap, yet we must confess to a preference for that made by the regular process of boiling as certainly the most reliable. We will, however, give what we consider the best processes for some of the others. Owing to the presence of some free sulphuric acid and other impurities, the oleic acid requires generally more alkali for its 8aponification, though it need not be entirely free from other salts or carbonic acid. Thus owing to its easy saponi-fication it is sometimes made in an extemporaneous way by simply adding the crystalline carbonate of soda to the olein, putting into an air-tight vessel having a stirrer, and under the pressure and agitation causing a rapid admixture, the water of crystallization being in sufficient quantity to form the soap. This process requires a close calculation of the several quantities and some experience to produce a good and uniform product. Being a cheap material and comparatively pure, it can be economically combined with other greases, such as kitchen and bone fats and other refuse greases. It also makes one of the most useful soft soaps for manufactures. For making a pure olein soap in a large way we will take say 6750 lbs. of oleic acid. The saponification is effected in a kettle of a capacity of 1870 to 2000 gallons, into which the oleic acid is introduced and melted with the help of a gentle heat. The acid being completely liquefied, pour into the kettle 125 gallons of new lye at 25°, and 250 gallons of lye of coction perfectly limpid at 25° to 30° B. It often happens that by the reaction of the lyes on the oleic acid, the mixture considerably thickens and forms a compact mass. This effect is due to the spontaneous formation of stearate and margarate of soda, but as the heat increases, the mixture becomes clear, the grains gradually disappear and the mass becomes fluid. Continue to keep up a gentle heat, and when the ebullition begins a considerable quantity of foam is developed on the surface of the soap. This effervescence is moderated either by slacking the heat, or by stirring all the time, or by pouring a few pails of cold water into the kettle. This rapid reaction is due to the action of the carbonate of soda, which, in contact with the oleic acid, abandons its carbonic acid. But this effect would not take place if the lyes used were entirely caustic. When this first effervescence has ceased, increase the heat, and continue to boil quickly ; care being taken to stir all the time. By continuing the ebullition, the lye becomes more and more concentrated by the evaporation. The nature of the paste is modified, and by a progressive saturation with alkali, it acquires consistency* 19 290 TECHNICAL TREATISE ON SOAP AND CANDLES. THE FABRICATION OF SOAPS. 291 However, when the pasting is finished, the paste has not the consistency of the ordinary soaps, which difference is explained by the nature of the oil on which we operate—this oleic acid being almost entirely formed of the oily and liquid part of the tallows, that is, of the part the least apt to form hard soaps. It is only after the paste is completely saturated with alkali that it forms a very consistent soap. This remark may be applied, at least generally, to every fatty or oily substance in which olein predominates. The time for the first operation, on 6700 lbs. of material, varies from ten to fifteen hours. It is ascertained that the pasting is terminated, when the grains of soap formed at the beginning of the operation are entirely dissolved; then the heat is stopped ofl", and after resting ten or twelve hours the lye is drawn off. Observations.—The pasting being finished, it is important to let the mass rest for ten or twelve hours, to permit the lye not combined with the soap to separate as completely as possible. If much of it is left in the paste, it will be troublesome in the coction, for two reasons : first, on account of the great quantity of neutral sails it contains, and which would render the soap less hard; then because it would weaken the degree of the new lyes of the first service, in such a manner that the action of these lyes on the olein would be less efficacious than if the operation had been conducted with a paste less saturated with neutral salts. Whilst colored, this sub-lye is generally limpid; but as it marks from 18° to 22° B., it has to be reduced to 8° or 10° by the addition of water. It is then left to settle for a few days, and passed through an old residuum of exhausted soda ash and lime. For 6700 pounds of oleic acid, the quantity of lyes drawn oft" after ten or twelve hours' rest, amounts to 175 to 200 gallons, and, though marking from 18° to 20° B., containing very little useful alkali but many other salts. The coction is effected with new caustic and concentrated lyes of soda ash. Two services are generally sufficient to bring the soap to the point of complete saturation. First Service of Lye.—All the lye of the first operation being drawn off, pour into the kettle from 225 to 250 gallons of fresh lye at 27° or 28° B. Heat and keep the mixture to boiling. At the beginning the ebullition must be gentle; too active boiling would dilate the mass considerably, or cause the soap to stick to the bottom of the kettle. Thus, for the first hours the kettle must boil gently. It is true the soap is separated from the lye but slightly; its grain ie not completely formed, and it is yet soft, flaccid, and dilated; but it is proper to have it so, for in this half-viscous state, the action of the lye on the oleieacid is more direct and more rapid than if the grain of the soap were prematurely formed. During all this first stage of the operation it is very important, we repeat, to boil gently and uniformly. A more complete and equal saturation of the oleic acid by the lye is obtained. The formation of too much foam is also to be avoided. Later—that is, after five or six hours of ebullition —the heat is progressively increased; by evaporation the lye concentrates, and the grain of the soap becomes larger and firmer. While the lyes do not separate as completely as in the first service, it is easy to see that the soap is not so viscous, and is less greasy than at the beginning of the operation. To render the separation more complete, and to compensate for the loss due to the evaporation, add every hour, for the first six hours, from ten to twelve gallons of new lye at 27° or 2^° B.; add also, towards the end of the first service, fifteen gallons of salted water at 25° B. This addition of salted water contracts the soap', and facilitates its separation from the excess of lye with which it is mixed. Lastly, after twelve or fifteen hours of continual ebullition turn off the heat, cover the kettle, and let it rest eight or ten hours. This time is necessary to have a complete separation. Draw off the lye, which is strongly colored brown, and marks while warm from 22° to 25° B.; frequently, on cooling, the lye solidities into a gelatinous mass. Alone, or mixed with new lye, it is used in the pasting of oleic acid. Second Service of Lye.—This service, which is generally the last, consists of new lye at 28° or 30° B. 293 292 TECHNICAL TREATISE ON SOAP AND CANDLES. The lye of the first service being drawn off, pour into the kettle about 175 gallons of new lye at 28° or 30° B. Heat; very soon the mass begins to boil; at first moderate the heat; but when, by an ebullition of five or six hours, the paste has acquired more consistency, the heat is increased; then add every hour, for six hours, about twelve gallons of lye of coction at 28° to 30° B. These successive additions of strong lyes have for their object the complete saturation of the soap, and to replace the evaporated water. Towards the end of the operation—that is, after an ebullition of twelve to fifteen hours, add, as in the first service, from twelve to fifteen gallons of salt water, at 25° B. By this addition, the paste becomes denser and harder; its great consistency presents obstacles to the ebullition, which then becomes tumultuous. The foam which covered the soap has entirely disappeared ; the soap is then in hard and dry grains, of a brownish color. However, the end of the operation is indicated by the following signs:— 1. When a little of the warm soap is put into the hand and quickly rubbed with the thumb, it instantaneously forms thin and hard scales, which fall from the hand without leav ing on it any adhering particles. 2. When the foam which covered the surface of the soap has disappeared. 3. When, after fifteen hours of continual ebullition, the lye is yet caustic. To obtain the soap well grained, it is necessary that the lye extracted from the kettle, at the end of the operation, should mark 28° to 30° B. When these indications are well defined, the soap is completely saturated wTith lye. Turn off the heat, cover the kettle, and, after resting ten hours, draw oft" the lye. Fitting.—For this operation, the lye of the pasting (em-patage) or a new lye can be used. The first slightly colors the soap, but deprives it more completely of the excess of caustic alkali it contains; the second does not color it, but sometimes causes an efflorescence of carbonate of soda; it is then better to use the first. As it generally marks from 18° THE FABRICATION OF SOAPS. to 20° B., it is reduced to 8° or 12° B., by diluting with water. The operation is conducted as follows:— Two men stir the paste continually, while a third pours in the lye at 8° to 12° B. Heat strongly, so as to keep the mixture very warm, for it is by the combined action of heat, stirring, and the successive additions of weak lyes that the grain of the soap is broken and refined, by depriving it of the excess of caustic alkali and saline substances it contains. It is only when the paste is sufficiently impregnated with weak lye, and has acquired a temperature near the boiling point, that it becomes homogeneous and fluid ; the soap has then the form of soft, dilated, and flat grains. Generally from 250 to 300 gallons of lye at 8° or 12° B., are used in the operation. When the soap is entirely melted and floats in the lye, boil the mixture gently for a few hours; and to prevent the soap from again becoming granular by the concentration of the lyes, add from time to time a few pailfuls of water or of lye at 2° or 3° B. In consequence of the movement caused by the ebullition, an abundant foam appears on the surface of the soap; this foam consists of the most impure parts of the paste, and is strongly salted. It is known that the operation is finished, when the paste which is under the foam is smooth, fluid, and homogeneous; the density of the lye at the bottom of the kettle is also a sign to indicate when the paste has been boiled long enough. When cold this lye marks from 17° to 18° B., at the end of the operation. If below 15°, the soap would be less consistent and less firm; above 19° or 20°, it would be too hard. Thus, the proper degree of density of the lye ought to be, when cold, from 17° to 18° B. This result being obtained, the heat is stopped off, and the kettle well covered, so as to retain the heat in the mass as long as possible—an essential condition for a complete separation of the saline matters and the lye. Indeed, if the cooling should be too rapid, not only will the soap not be deprived of its heterogeneous and saline parts, but it will 291 Previous Next
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