The greatest improvernent is due to the discovery that the dark membranous matters may be oxidized while the fat is still neutral. The acidification, oxidation, and decomposition are all now conducted, in rapid succession, in one and the same wooden tank, after which, one or two washings in another tank render the fatty-acids fit for the press.
Another point of great practical importance, which has been developed in the working out of this process, is the increased hardness of the stearic acid produced by it, arising from the solidifica tion of some of the oleic acid in the tallow, by the prolonged act:on of sulphuric acid upon it. This reaction has lately been pointed out as a novelty, by Bornemann and Kraut ; hut it was suspected twelve years ago, and soon afterwards was definitely proved, by the Messrs. Bock. They observed that the fatty-acids became harder and harder, so that cold pressure had no effect upon them ; by the adoption of hot-pressing, they produced white atomic acid, and an exceedingly brown oil. This latter, when distilled, saved the cost of distillation, by its yield of solid matters. It is claimed, therefore, for the Bock process, that stearic acid can be made of better quality and in larger quan tity from a given weight of tallow, than by any other process. at present known.
Whichever of the four processes (lime-saponification, autoclave, distillation, or Bock's) is employed, a large proportion of oleic acid is unavoidably produced. The quantity of it, per ton of neutral fat, varies in inverse proportion to the hardness of the original fat, or of the niaterial manu factured from that fat. For many years, it was difficult, at any rate in England, where soft soaps are much less used than on the Continent, to find a suitable outlet for this oleic acid : it could not be used as a lubricant, owing to its acid reaction upon metals ; when saponified by the ordinary methods, it produced a very soft and very brown soap, slow of sale. It was discovered, however,
that when saponified with soda-leys of very high specific gravity, a hard soap could be made from it, containing a very large percentage of fatty-acids, and good for ordinary cleansing purposes, but whose smell was considered objectionable. A few years ago, M. Radisson, of Lyons, taking advantage of a laboratory reaction of oleic acid which had long been known, developed a method of converting it into palrnitic acid, and, by dint of great perseverance, worked out the details of the process on an industrial scale ; it is now a commercial success, and has been patented in nearly all countries where candles are manufactured. Whether it is more economical to convert the oleic acid into soap or into palmitic acid, depends upon the relative cost of the two processes, and the current market value of tho manufactured products.
The following information relative to this remarkable process, which is extremely interesting, from both scientific and technological points of view, was kindly supplied to the writer, by the patentee, M. St. Cyr Radisson, 37, Boulevard-Oddo, Marseilles.
In 1841, Warentrapp announced that when oleic acid was heated with a great excess of caustic potash, it was decomposed into palmitic acid, acetic acid, and hydrogen, the acids combining with the potash, the reaction being explained by the following formula :— 01-ic acid. Potash. Palmitate of Potash. Acetate of Potash. Hydrogen.