It must be granted that the minutely correct determination of the constitution 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 fuer Praktische Chemie.

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ON THE NATURAL FATS.

BY DR. CHARLES LOeWIG.

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 (butter, 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 class 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 canals 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.