Part 35 (2/2)

The fluid runs from the fatty acids on the filter, which, with the was.h.i.+ngs, has been preserved in a sufficiently large beaker gla.s.s, is colored with tincture of litmus, and decomposed with a test alkaline solution until the blue color appears. The difference of the quant.i.ty of alkali required to neutralize the sulphuric acid, and the quant.i.ty of sulphuric acid used in the first instance, allows a calculation to be made as to the quant.i.ty of effective alkali in the soap, for example:--

23.86 grms. of soap (partly cocoa-nut oil soap).

17.95 ” fatty acids with filter.

04.44 ”filter.

----- 13.51 grms. of hydrates of fatty acids = 56.62 per cent.

28.00 cub. cent. of the diluted sulphuric acid applied for the decomposition of the soap, of which 100 cub. cent.

represent 2982 grms. of carbonate of soda.

17.55 cub. cent. of alkaline fluid, which were used for the saturation of the above acid, and of which 100 cub.

cent. saturate an equal quant.i.ty of that acid.

---- 10.45 cub. cent. of the sulphuric necessary for the alkali contained in the soap, representing 0.1823 grms. of soda = 7.64 per cent.

A determination of the alkali as a sulphate afforded in another portion of soap 9.57 per cent. of soda, because the sulphate of soda and chloride of sodium present in the soap gave up their alkali.

The alkaline fluid applied by me was a saccharine solution of lime, which can be naturally replaced by a solution of soda, and must be if the chloride of sodium and sulphate of soda mixed with the soap shall be determined in the following way:--

The fluid again exactly neutralized with alkali is evaporated to dryness, and the residue gently heated to redness. As in the above manipulation, the fluid was not heated to the boiling point, the original chloride of sodium and sulphate of soda are contained in the weighed residue, besides the soda of the soap and that which has been added with the sulphuric acid, forming sulphate of soda. A second exposure to a red heat with sulphuric acid converts the whole residue into sulphate of soda, and from the increase of weight, by a comparison of the equivalents of NaCl and NaO, SO_{3} the quant.i.ty of the former may be decided. According to the equivalents which Kopp furnished in 1850, the increase of weight to the chloride of sodium is as 1:4.68. The original sulphate of soda must be, lastly, found by the subtraction of the same salt formed plus the calculated chloride of sodium from the first heated residue.

In practice, it is seldom necessary to proceed with the determination of the chloride of sodium and sulphate of soda, except with stirred and cocoa-nut oil soaps; certainly less of the truth is seen if, after the above determination of the fatty acids and the effective alkali, the absent per centage of water is introduced in the calculation, than if the water is reckoned, which is never completely evolved from soap, even technically prepared at 302 Fahr., and another determination made of the fatty acids or alkali _en bloc_ the fatty acids, or even the alkaline contents.

The method here given partakes of the usual imperfections, that the fatty acids as well as the unsaponified soap are equally estimated, and the mixed hydrate or carbonate of the alkali as well as the combined alkali. The presence of the carbonate can be easily recognized by the foaming of the soap solution, upon the addition of the sulphuric acid.

These imperfections, however, are of little importance.

It must be granted that the minutely correct determination of the const.i.tution of soap must be always yielded up to those who are technically conversant with this department of chemistry, the estimation of free alkali and unchanged fat excluded in, at least, by certain ages of the soap. Further, a considerable excess of one or another ingredient soon betrays itself by a corresponding departure in the soap of the characteristic properties of a good product, and a small excess can be judged sufficiently exact from the proportion of the alkali, which, supposing soda present, should not amount to more than 13 per cent. with a pure cocoa-nut oil soap, not less than 11.5 per cent. with a tallow soap; but with palm oil and mixed soaps the one or the other limit approximates.--_Journal fur Praktische Chemie._

ON THE NATURAL FATS.

BY DR. CHARLES LoWIG.

The fats which exist in nature can be divided into the general and the special; the former exist in almost all plants and parts of plants; the latter includes only some vegetable substances, as _laurostearine_, _myristicine_, and _palmatine_. The consistence of fats of the general kind depend upon the proportions of margarine, stearine, and oleine contained in them. The former preponderate in the solid fats (b.u.t.ter, lard, and tallow); and the latter in the fluid ones or oils. According as an oil contains oleic acid or olinic acid, it is termed a fatty or drying oil. To the cla.s.s of fatty oils belong olive, almond, hazel-nut, beech, rape oils, &c.; to that of drying oils, linseed, nut, hemp, poppy, grape-seed, oils, &c.; which are used for varnishes.

In the vegetable kingdom the fats are chiefly in the seeds and in their coverings, seldom in the perispemium (poppy), and in the fleshy substance surrounding the seed (olive). The fat in the seed is mostly enclosed in cells with a proteine compound. In the animal kingdom certain parts of the body are quite filled with fat-cells, particularly under the skin (_Paniculus adiposus_), in the cavities of the abdomen, in the so-called _omentum_, in the kidneys and the tubulated ca.n.a.ls of the bones. Fat is also enclosed in cells (fatty globules) in milk.

It is established, without a doubt, that a greater portion of the fat which exists in the animal kingdom originates from the vegetable kingdom, for it is introduced into the body cotemporaneously with the proteine compounds of that kingdom. A portion of the fat as well as wax is formed in the animal organismus, as shown by a number of observations, and in most cases it is unquestionable that the non-nitrogenous nutriments, as starch, serve for the formation of fat by a process of deoxidation; nevertheless, the formation of fat in the animal body appears only to take place when the substances containing starch enter the body simultaneously with fat.

If the fat existing in the animal body is contained in cellular tissue, its separation may be simply effected by placing the incised tissue in hot water. The cells burst and the fat collects itself on the surface of the water. If vegetable substances contain fat in large quant.i.ty, as, for example, seeds, it may be obtained by expression. The dried seeds are bruised and expressed between either cold or hot metallic plates.

Olives are laid in heaps before expression; when they begin to ferment, they can be completely expressed. If animal and vegetable substances contain only a little fat, it must be extracted by ether.

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