It will be observed that three processes for the decomposition of neutral fats have now been described—viz. (1) By saponification with. a strong alkali, at a temperature hut little above 100° (212° F.) ; (2) By the use of water, with or without a very small quantity of lime, at very great steam pressure, and a correspondingly high temperature ; (3) By treatment with strong sulphuric acid and water in successive portions, subsequent distillation at normal atmospheric pressure, hut at a dangerously high temperature—above 300° (572° F.). It was reserved for a physician at the Danish Court, the late Dr. J. C. A. Buck, to demonstrate the important fact that, hy properly conducting the operation, water alone might be made to decompose tallow into fatty-acids and glycerine, and that by the use of water and sulphuric acid combined, fatty-acids might be prepared from tallow in open lead lined tanks furnished with steam coils,—without any of the complicated and dangerous apparatus required hy the " autoclave" or the " distillation " processes, without any lime or other alkali, and with a much less expenditure of acid than was required by any other process. Unlike many inven tors, he was able to carry out his ideas into actual practice, and in the International Exhibition held in London in 1862, were shown some beautifully white and hard stearic acid candles, which had been prepared by this process in the manufactory of O. F. Asp, Prindsessegade, Copenhagen. Since then, the process has been constantly at work in that factory ; it has also been adopted in several other continental candle factories, and is now at work, among other places, in Ncw Zealand. The simple character of the " plant " required renders it peculiarly valuable for distant countries. Considered from a theoretical point of view, it is, perhaps, the most ingenious and the most strictly scientific of all the methods for decornposing neutral fats.
Dr. Bock pointed out, that tallow is composed of exceedingly minute globules of fat, surrounded by membranous envelopes, composed, probably, of albumen ; and that until these enveloping walls aro destroyed, no reagent can act upon the fat within. In ordinary saponification, the albuminous envelopes are dissolved by the caustic alkali ; in acidification, they are burnt and charred by the strong sulphuric acid, the quantity of which may bs so adjusted as not to burn and discolour the tallow itself, which. after pouring out from the destroyed envelopes, is in a state to he readily decom posed by water at 100° (212° F.). Dr. Bock's process was described by him in an article in Dingler's Polytechnisches Journal,' for Msy, 1873, of which ths following is a synopsis.
" By the lime saponification plan, the albumen contained in the fat is dissolved, lime-soap is formed, and the extraction of the glycerine is rendered possible. By acidification, the whole pro cess is effected at once. Conducted properly, the fat, washed out with water, always remains as neutral fat, and, by the use of concentrated sulphuric acid, not a trace of glycerine is left. Acidi fication. rationally conducted, is only a preliminary operation, intended to break up, corrode, or carbonize, the albumeniferous matters. But the conduct of the operation was long based on the erroneous belief that a double acid, sulpho-stearic, was formed. With due care, only the envelopes
of the cells are blackened, and these are soluble neither in fat nor in fatty-acids. The production of a real black solution is only au evidence that a certain part of the fat has been burnt, which should be avoii led under all circumstances. There is no doubt that the operation has generally been carried to excess, in the matters of duration, height of temperature, or strength of acid. By proper acidifi cation, the neutral fat is only unclothed, as it were, and freed from the cells, or at any rate, the latter are so ruptured, as to allow of the easy exit of the fat. This latter is then in a condition to be decomposed, an operation sccomplished in much shorter time by the chemical equivalent of acid 4 to 4.5 per cent.—and the necessary water. After letting out the glycerine waters, the fatty-acids appear more or less black. They may now be distilled. Their melting-point varies from 49° to 57° (120° to 134° F.).
" The real value of Dr. Bock's method consists in dispensing with distillation. The object of this operation is the removal of the black colour, or rather of the black-coloured matters, by superheated steam. These black 'natters are the partially carbonized albumen cells, which swim about iu the fatty-acids bccause the sp. gr. of the two bodies is about the same. This difficulty is overcome by oxidizing the mass, by which the sp. gr. of the cells is raised from 0.9 to 1.3. They are tl.us precipitated, and the fatty matters can be washed off. The subsequent cold and hot pressing are the same as with ordinary methods.
"From several years' experience at Messrs. Asp's works, the following results have been deduccd• Tallow yields, by complete decomposition, 95 per cent. of fatty-acids, which lose 2 per cent. by oxidation and washing. The glycerine obtained equals 61 per cent. from tallow at 23° B., and is quite free from all organic acids. The oleic acid resembles that produced by the lime saponification process; but it is much richer in solid acid. The stearic acid is also like that produced by the litne saponific a-ion method ; brit it is much harder, and its melting-point is 58°-60° (136°-140° F.). It equals 55-60 per cent. of the tallow employed.
" The plan is free from danger, as the steam is only used in open vessels. The plant is much cheaper, as nothing special is required. The labour also is much reduced, as the operation is com pleted in one vessel. It is as applicable to vegetable as to animal fats." The process indicated abovd has now been for fourteen years in daily operation on a manufac turing scale in Copenhagen, and in the hands of the inventor and his son, has been greatly im proved and simplified since its first introduction. At that time, there were five stages in the process, viz. :—(1) Acidification, to remove the membranous cellular tissue from the tallow ; (2) Decompo sition, by acidulated water, into dark fatty-acids and glycerine ; (3) Oxidation, to increase the sp. gr. of the dark membranous matters, so that they might separatVhemselves from the fatty-acids ; (4) Repeated washings with water ; (5) Pressing, both cold and hot.