 |
Home > TECHNICAL TREATISE ON SOAP AND...
Previous Next The best candle and soap tips online! TECHNICAL TREATISE ON SOAP AND CANDLES. SOAP ANALYSIS. S57 from the rest, by the above stated process, the proportion between the potash and soda is calculated. The quantities thus found are to be doubled for the soap which is tested We have yet to consider the residuum, which in dissolving in distilled water remains upon the filter. It consists of carbonate of lime, carbonate of dolomite, clay, and silicic acid. Its quantity is as a rule very small, and the determination of these substances can be taken simultaneously, by taking the dried precipitate from the filter, calcining in a platina crucible and burning the filter, and weighing the whole. Another method for determining the alkalies combined with the sebacic acids, has the advantage that the potash is at least directly determined, and consists in this: The alcoholic soap-solution is evaporated by the volatilization of the alcohol, diluting with water; the solution is decomposed by oxalic acid to a weak acidy reaction, the sebacic acids are separated, the liquid evaporated to dryness, the residue calcined, and the coaled mass completely washed out with distilled water. It is now filtered, the coal washed out and determined in the filter, the value of the alkali by titrating with a solution of tartaric acid (75 grammes (2.63 ozs.)to 1000 cubic centimetres (1 litre == 2.1 pints) dissolved), then adding of the solution of tartaric aeid again as much as had been used for neutralization, evaporating the liquid in the water-bath until dry, cooling to the temperature of the room, and treating the salt residue saturated at the same temperature with a solution of bitartrate of potassa. This now dissolves the foreign salts, and leaves the potash as bitartrate of potash, which ia dried by a gentle heat, and then weighed. From the weight the potash contained therein is calculated. 100 parts of the dried bitartrate of potassa correspond to 25.04 potash. If the potash thus found ia deducted from the aggregate quantity of the alkalies, obtained by titration with tartaric acid, then the rest is soda. By the chloride of platinum also, the potash can be directly determined; this method is however rather expensive. For discerning the free alkalies in soap, Stein has proposed a very simple method, by which it becomes obvious, without further trouble, whether free alkali is present or not. Stein applies to this end corrosive sublimate (bichloride of mercury), which furnishes with the sebacic acid a white sebacic peroxyd of mercury combination, while in the absence of a free alkali (caustic as well as carbonate) red peroxyd of mercury is formed. Stags has proposed for this same purpose calomel, which, if free alkali be present, becomes black. The sublimate has however the advantage over calomel, that it can be applied in solution, and also that soaps may be tested with it without dissolving them, by moistening a fresh cut surface with a solution of sublimate. On the other hand, for determining the free alkalies in rosin soaps, binitrateof mercury is well adapted. By its application for testing rosin soaps, the heating of the liquid must be avoided, because by the resinous acid protoxyd of mercury may suffer a decomposition. Determination of the Amount of Sebacic Acids and of the Rosin.—For this operation the sebacic acids may be used, as we have separated them by the two preceding methods. Especial care must be taken that no loss is incurred, which might easily happen, because the sebacic acid will adhere to the sides of the vessels, and from thence cannot be again removed by water and be regained. This is attained by washing with benzine, which by heat is entirely volatilized again. If by this means all sebacic acid has become reunited, the sebacic acids are melted, thus ejecting the adhering water and benzine. But these acids being mostly too soft to be accurately weighed, they are usually melted together, with dried white candleshop.com/cgi-bin/affiliates/clickthru.cgi?id=soforreal">wax or stearic acid, which substances have been previously accurately weighed. The fat cake is placed upon a filter, and washed out with distilled water, until the washing water is no longer acid. The drying is performed under a glass cover with concentrated sulphuric acid. The drying may also be performed in a porcelain saucer over a water bath, and can be continued as long as the saucer no longer loses in weight, whereupon the melted acid is poured out, the saucer cleansed with a little lye, dryed off, and when thus empty is weighed. From the aggre- 358 TECHNICAL TREATISE ON SOAP AND CANDLES. SOAP ANALYSIS. 359 gate weight is deducted in the first place that of the candleshop.com/cgi-bin/affiliates/clickthru.cgi?id=soforreal">wax or stearic acid. The rest represents the hydrates of sebacic acid, in case rosin soap is not investigated. The hydrates of stearic acid, palmitic acid, and oleic acid have nearly the same value of water, which with sufficient accuracy may be placed at 3.25 per cent. From the weight of sebacic acid found, 3.25 per cent, are therefore deducted and the rest as the sebacic acid is taken into the analysis. Very frequently it happens, that the hydrate of the sebacic acids is not deducted, and the hydrates of the same anhydrous sebacic acids calculated. By the error thus committed, the value of the sebacie acid in the soap appears too high. Under certain circumstances the melting points of the various acids may give a basis as to the kind and derivation of the sebacic acids, especially \Hthe point in question is to determine whether two samples of soaj,; before us are equal or varying. For this experiment a small quantity of sebacic acid is melted and the temperature observed. While slowly cooling off", the mercury in the thermometer will be observed remaining somewhat longer at a fixed degree, whenever the point of congelation is reached, and the temperature thus indicated is the melting point. If but little of the sebacic acid is at our disposal, then according to Douis we operate as follows: A thin glass tube is taken, drawn out to a very narrow tube, and the narrower part, which is turned downward, is filled up with the melted acid. After the congealing has taken place, the apparatus is placed in water, which is slowly heated. At the moment of melting, the partly melted sebacic acid is forced upward by the pressure of the water. The temperature of the water, at which this observation takes place, is also the melting point of the acid. According to Stockhardt the sebacic acids congeal as follows:— of pure tallow soap of pure palm oil soap of 1 part tallow and J part cocoa oil of 1 part tallow and ^ " " of 1 part tallow and 1 " " of 1 part palm and £ " " of pure cocoa-nut oil at 44o to 450 c. (111.20 to 1130 F.) at 380 to 39O 0. (IOO.40 to 102.20 F.) at 32o to 35O C. ( 89. C° to 95= F.) at 39O to 300 C. ( 84.2o to 860 p.) at 27O to 28° C. ( 80.60 to 82.40 F.) at 270 to 280 C. ( 80.GO to 82.4° F.) at 28O to 240 C. ( 73.4O to 75.2° p.) A less accurate, but for all common cases amply sufficient method to determine the value of sebacic acid in a soap, when the separated fat, instead of being weighed, is measured, has been proposed by Buchner. To this end is used an alembic of glass, with a long and not too wide neck in which is inserted a scale graduated into 1 cubic centimetres (0.054 flui-drachm). In this apparatus are placed 16 § grammes (0.58 ounce) soap, with diluted muriatic acid, and heated. If the decomposition is perfect, lukewarm water is used to fill up, until the division mark between the watery and the fatty layer reaches the zero point of the scale, or is somewhat above it. After leaving it to cool off to the temperature of the room, the height of the fatty layer is read. If the specific gravity of sebacic acid is calculated at 0.93 and multiplied by the indicated cubic centimetres,we obtain the weight of the hydrates of the sebacic acid, and can thereby calculate the quantity of fat which has been applied in the fabrication of the soap. According to Buchner, 50 kilog. (110 lbs.) fat furnish 77J kilog. (170.5 lbs.) of the fine grain soap, and about r'g glycerine. For an easy mode of calculation, Buchner furnishes the following table:— Previous Next
|
|
