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Updated: May 25, 2025
The principal methods which comply with these demands have been carefully studied by Hueble for the purpose of discovering a process of general application; methods founded on the determination of density, freezing, and melting point were compared with those dependent on the solubility of fatty substances in glacial acetic acid or a mixture of alcohol and acetic acid; also the method of Hehner for testing of butter, the determination of glycerine and oleic acid, and at length the process of saponification.
Solution. We have already seen that when a salt of any kind dissolves in water, heat is absorbed, and becomes latent; in other words, cold is produced. I will describe a remarkable example or experiment, well illustrating this fact. As regards solubility, some salts and substances are much more quickly and easily dissolved than others.
In order to avoid the expense and trouble consequent on the latter process, some manufacturers add alkali, by which means the free fatty acids are saponified, and the fat is held in a state of emulsion, thus giving the cocoa a false appearance of solubility.
Thirdly, That most of the simple ideas that make up our complex ideas of substances, when truly considered, are only POWERS, however we are apt to take them for positive qualities; v.g. the greatest part of the ideas that make our complex idea of GOLD are yellowness, great weight, ductility, fusibility, and solubility in AQUA REGIA, &c., all united together in an unknown SUBSTRATUM: all which ideas are nothing else but so many relations to other substances; and are not really in the gold, considered barely in itself, though they depend on those real and primary qualities of its internal constitution, whereby it has a fitness differently to operate, and be operated on by several other substances.
As I noticed before, the better plan of distinguishing a mineral is by being familiar with its appearance, but as this is generally impracticable, I will detail the modes used in lieu of this to be applied on bringing the minerals home. These distinguishments depend on difference in specific gravity, hardness, solubility in hot acids, and the action of high heat.
The method of analysis that I am about to describe is based chiefly upon the determination of the melting point of the fatty acids contained in the oils, and upon their solubility in a mixture of alcohol and acetic acid. The oils employed in adulterating olive oil, and to which regard must be had in testing it, are the following: Cotton seed oil, sesame, peanut, sun flower, rape, and castor oils.
He shows that the iodide may resist heat, and that the loss of color depends on the greater attraction of water for iodine as compared with starch, and the greater solubility of iodine in water at high temperatures. That from the potato arum gives a blue, and that from wheat and rice a violet tint; while the filtrate from starch paste, from whatever source, always gives a blue color. By Mr.
Such are the essential facts of osmosis. We may seek to interpret them and to thoroughly examine the mechanism of the phenomenon; but it must be acknowledged that as regards this point, physicists are not entirely in accord. In the opinion of Professor Nernst, the permeability of semi-permeable membranes is simply due to differences of solubility in one of the substances of the membrane itself.
We may now proceed to consider sulphureous substances, with regard to their solubility in water, and to the part which these bodies have acted in consolidating the strata of the globe. The sulphureous substances here meant to be considered, are substances not soluble in, water, so far as we know, but fusible by heat, and inflammable or combustible by means of heat and vital air.
This case affords one of the best illustrations of the effect of an excess of a precipitant in decreasing the solubility of a precipitate. It should be borne in mind that the quantity of barium sulphate in this !saturated solution is a constant quantity! for the existing conditions.
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