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Page:Popular Science Monthly Volume 23.djvu/838

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THE POPULAR SCIENCE MONTHLY.

The foregoing paper was written several months ago, and since that time important contributions to the subject have been made by Geddes, Hamann, Jickeli, Entz, and especially by Brandt. The latter has published a summary of the whole matter, enriching it by observations of his own made at the zoölogical station at Naples. Brandt attaches less physiological significance to symbiosis than does Geddes, from whom he still differs in considering even Hydra and Spongilla as symbiotic and not "vegetating" animals. At present the views of Brandt, as laid down in his last paper (see "Mitt, aus zool. Stat. Neapel," iv, ii, 1883), seem likely to prevail; and in that article the student will find a complete literature and a full discussion of the whole subject.

 

THE CHEMISTRY OF COOKERY.
By W. MATTIEU WILLIAMS.
XIII.

THE process of frying follows next in natural order to those of roasting and grilling. A little reflection will show that in frying the heat is not communicated to the food by radiation from a heated surface at some distance, but by direct contact with the heating medium, which is the hot fat commonly, but erroneously, described as "boiling fat."

As these papers are intended for intelligent readers who desire to understand the philosophy of the common processes of cookery, so far as they are understandable, this fallacy concerning boiling fat should be pushed aside at once.

Generally speaking, ordinary animal fats are not boilable under the pressure of our atmosphere (one of the constituent fatty acids of butter, butyric acid, is an exception; it boils at 314° Fahr.). Before their boiling-point, i. e., the temperature at which they pass completely into the state of vapor, is reached, their constituents are more or less dissociated or separated by the repulsive agency of the heat, new compounds being in many cases formed by recombinations of their elements.

When water is heated to 212° it is converted completely into a gas, which gas returns to the fluid state without any loss on cooling below 212°. In like manner if we raise an essential-oil, such as turpentine, to 320°, or oil of peppermint to 340°, or orange-peel oil to 345°, or patchouli to 489°, and other such oils to various other temperatures, they pass into a state of vapor, and these vapors, when cooled, recondense into their original form of liquid oil without alteration. Hence they are called "volatile oils," while the greasy oils which can not