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312

MANUFACTURE OF FATTY ACIDS FOR CANDLES.

Marine soap was a name given to a cocoa-nut oil soap commonly containing excess of caustic or carbonated alkali, which enabled it to be used with sea water.

Curd soap is usually obtained from tallow only, a small portion of olive oil or of lard being sometimes added. The soap while hot is put into a pan and crutched, or stirred forcibly, to break up the grain; it is then conveyed to the frames. When cut it should be perfectly smooth and white. Yellow soap is made from tallow and palm oil, and in addition to the alkali and fat, contains a considerable proportion of common rosin, which possesses acid properties and unites with the alkali; it is manufactured by a process similar to that used for mottled soap, but instead of being cleansed, or put into the frames immediately after boiling, it is fitted, or mixed in the copper with a small quantity of water, which in two or three days carries down the excess of alkali, forming the negur, which subsides to the bottom; while a spongy crust, termed the fob, rises to the surface. The fob is skimmed off, and the semi-solid pasty mass of soap is transferred to the frames. The negur and fob are added to the next boil.

Marseilles and Castile soaps are made from olive oil and soda; they are mottled by the addition of green vitriol and sulphuretted ley to the soap while in the pasty state.

(d) Manufacture of Fatty Acids for Candles.

(1234) Large quantities of the fats are converted into the form of free acids, in the manufacture of what are often incorrectly termed stearin candles. This branch of industry has within the last few years acquired enormous magnitude. The fatty acids are prepared for this purpose by three principal methods:in the first of these processes the fat is saponified by means of lime; in the second the fat or oil is decomposed by sulphuric acid; and in the third process the fat is separated into glycerin and the fatty acid, under the influence of water at an elevated temperature. The acids furnished by the fats are, at ordinary temperatures, whiter and harder than the fats from which they are obtained, and they are at the same time cleaner and more combustible.

1. Saponification by Lime.-Until recently it was the general practice to saponify the oils or fats by means of lime, which readily effects the desired change, and has the advantage of being much cheaper than either potash or soda: this process is still

ACIDIFICATION OF THE FATS BY SULPHURIC ACID.

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The tallow is melted by in

extensively followed in France. jecting hot steam into the vat which contains it, and milk of lime is added; the whole being maintained at the temperature of 212° by continually injecting steam through a perforated pipe, whilst the mixture is kept constantly stirred. An insoluble calcium soap is thus formed; it is drained from the solution of glycerin, and then decomposed by the cautious addition of sulphuric acid diluted to the sp. gr. 1160. The melted fatty acids thus rise in the form of an oil to the surface of the heated mixture; they are now decanted, and are washed, first with a fresh portion of heated dilute sulphuric acid, and afterwards with water. The fused acids are then cast into thin plates or cakes not much exceeding an inch (25 millim.) in thickness; these cakes when cold are placed between layers of cocoa-nut matting, and are piled up one above another with iron plates interposed between every four or five cakes, and the pile thus formed is subjected to intense pressure by the aid of a powerful hydraulic press. By this means the oleic acid is in great measure forced out, whilst the harder palmitic and stearic acids remain, and are afterwards subjected to pressure at a higher temperature; a fresh portion of the more fusible fat is removed by this operation, and the residue becomes beautifully white. In order to remove any traces of oxide of iron which the fat may have absorbed from the machinery, it is again washed, first with warm dilute sulphuric acid, then with water, and finally is melted and moulded into candles. The oleic acid furnishes with soda a soap sufficiently hard to be used for many purposes in the arts.

M. De Milly has ascertained that the complete saponification of fats may be effected by a proportion of lime not exceeding 4 per cent. of the weight of the fat, by exposing the mixture, in a Papin's digester, with water, to a high temperature. This temperature, according to Pelouze, need not be higher than from 311° (155° C.) to 329°. If water alone be employed to effect the decomposition, a temperature of not less than 428° (220° C.), prolonged for many hours, is needed.

(1235) 2. Acidification of the Fats by Sulphuric Acid.-The action of sulphuric acid upon the fixed oils has been particularly examined by Fremy (Ann. de Chimie, II. lxv. 113). When concentrated sulphuric acid is made to act at ordinary temperatures upon an oil or fat, the fat at first combines with the acid, and the compound thus formed gradually becomes decomposed into sulpho-glyceric (1239), sulpholeic, sulphopalmitic, and sulphostearic acids.

The last three sulpho-acids are insoluble in acidulated

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ACTION OF SULPHURIC ACID ON FATS AND OILS.

water, but are dissolved by pure cold water. They have an oily bitter taste. On raising the temperature of the solution, they become decomposed, the sulphuric acid is set at liberty, and the glycerin and the fatty acids are separated. The sulpholeic acid is more permanent than the sulpho-compounds of the solid fatty acids.

If the sulphuric acid and the oil or fat be made to act upon each other at a high temperature, the fat is immediately broken up into glycerin and the fatty acids, whilst the glycerin is in its turn decomposed, at the expense of a portion of the sulphuric acid, and sulphurous and carbonic anhydrides are evolved. This reaction is employed on a large scale for the preparation of the so-called composite or stearin candles, and in England it has very nearly superseded the lime process.

The following is an outline of the method in which sulphuric acid is applied for this purpose by Messrs. Wilson at the works of Price's Patent Candle Company :-The fat is first melted and freed from impurities, then mixed with from one-twelfth to oneseventeenth of its weight of oil of vitriol in large copper boilers, where it is raised gradually by means of a current of highly heated steam to a temperature of about 350° (177° C.). This temperature is maintained for about two hours, the mass being frequently stirred briskly; during this process carbonic and sulphurous anhydrides are disengaged in large quantities, nearly all the glycerin and sulphuric acid being decomposed in the course of the operation. The liberated fatty acids are of a dark colour, and require thorough washing with water to free them from adhering sulphuric acid.

The impure fatty acids thus obtained are then subjected to distillation, which is effected by placing them in a copper vessel, into the lower part of which a current of steam at the ordinary pressure is injected; previous to its admission to the still this steam is heated to about 600° (316° C.), by transmitting it through pipes heated nearly to redness. The distillation does not take place below 400° (204° C.), but towards the latter part of the process the temperature frequently rises to 500° (260° C.). After the acidified fats have been distilled as far as is advantageous, the dark residue in the retort may yet be made to yield a considerable amount of fat by submitting it to pressure; the black solid mass which still remains is used as fuel. The distilled fat is broken up into fragments, and distributed in layers of about three-fourths of an inch in thickness upon squares of cocoa-nut matting, which are piled one above another, and submitted to the

ACTION OF SUPERHEATED STEAM ON FATS.

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action of a hydraulic press. The fat thus obtained is sufficiently firm to be made at once into candles suited to European climates, but for the Indian market it is necessary again to subject the fat to pressure, which this time is effected at a temperature of 122° (50° C.).

(1236) 3. Action of Water at a high Temperature on Fats and Oils.-Mr. Tilghmann a few years ago made the important observation, that when a mixture of fat and water is forced under strong pressure through tubes heated nearly to redness, so as to raise the temperature of the mass to 400° or 500° (260° C.), the fat is entirely decomposed into glycerin and fatty acids; the elements of water enter into combination with those of the fat, so that by this means a result is obtained exactly the reverse of that effected by Berthelot at lower temperatures (1240), when the acid and glycerin are digested together.

Mr. Wilson by injecting superheated steam at a temperature of between 500° and 600° into heated fat, was able to produce a similar separation of hydrated glycerin and of the acids with which it was previously in combination, and at the same time he succeeded in effecting the distillation, not only of the fat, but also of the glycerin; the latter is thus obtained in a high degree of concentration, as a beautiful, colourless, syrupy liquid, which can be prepared in almost unlimited quantity. The fatty acids are also procured by the same operation in a very pure form, so that this process, from its simplicity, and from the purity of the products which it yields, bids fair to supersede those previously employed in the preparation of the fatty acids for illuminating purposes. The operation, however, cannot be conducted so rapidly as the process of decomposition by sulphuric acid.

§ II. THE GLYCERINS-GLYCERIDES.

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(1237) At present only two forms of glycerin are known: normal glycerin or trityl-glycerin (Є,H,,H ̧Ð ̧), which is by much the most important, and amyl-glycerin (E,H,,H ̧ ̧), recently formed by Wurtz by the following reactions :-First, bromamylene dibromide, when heated with silver acetate, furnishes the bromamylglycol diacetate :

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And then by heating this new diacetate with caustic potash, bromamylglycol is first produced, with potassic acetate :—

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Finally, an excess of caustic potash transforms bromamylglycol into amylglycerin with elimination of potassic bromide :

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(1238) GLYCERIN [(ЄH ̧Ð ̧, or CHO), the Sweet Principle of Oils. Sp. gr. 1.28 at 59° (15° C.)].-This substance is separated from all fatty and oily bodies (with the exception of spermaceti and the different varieties of wax), during their saponification by alkalies. According to Pasteur it is also formed in small quantities during the process of alcoholic fermentation. Glycerin is a viscid, colourless liquid of a sweet taste, soluble in water and alcohol in all proportions, but sparingly soluble in ether. It dissolves most of the deliquescent salts, as well as many other substances which are soluble in water. Baryta, lime, and strontia are freely soluble in glycerin, and the solutions are not precipitated by carbonic anhydride. Glycerin is slightly volatile at 2120, but, if distilled alone, the greater part of it experiences decomposition, with disengagement of intensely pungent vapours of acrolein (ЄH1; 1242), which excites a most painful irritation of the eyes. When heated sufficiently in air, glycerin burns with a luminous flame. It may, however, be distilled without alteration, in a current of superheated steam which has been raised to a temperature of between 500° and 600°; advantage is taken of this fact in order to prepare glycerin in large quantities (1236). The usual method of obtaining glycerin on a small scale consists in saponifying olive oil by heating it with an equal weight of litharge: the oxide of lead is mixed with water and added to the oil, with which it is boiled till the saponification is complete fresh portions of water being added from time to time to supply the place of that which is evaporated. The glycerin is dissolved by the water, and is easily freed from the insoluble lead plaster, or mixed oleate and margarate of lead which is formed. The aqueous solution retains a small quantity of oxide of lead, which may be separated by transmitting through it a

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