Page:Popular Science Monthly Volume 17.djvu/878

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with mean temperatures of 77·5° and 77·7°. These figures give a variation of less than 6° in a year, and to this limited range is ascribed the debilitating nature of the climate. The mean pressure of the barometer for four years differed but a thousandth of an inch from that indicated at the equator. The coast of the mainland of Africa, Dr. Robb says, is undoubtedly prejudicial to health, and both Europeans and natives of India who pass any considerable time there suffer severely from fever of a bad remittent type, and from dysentery. All seasons are bad, but some are better than others, and travelers going into the interior are usually advised to leave the coast-region before the heavy rains begin to fall. The seeds of disease are often sown by even a short residence on the coast, and the traveler dies before he has advanced many marches into the interior. Travelers, therefore, should always make a careful and quick march across the unhealthy belt of country along the coast, and pitch their camps in the higher and drier districts beyond; and, if they have to linger on the coast, they should take care to pass their nights in the safest places they can find.


Application of Cold in Industrial Chemistry.—Heat, of temperatures above the freezing-point of water, has long been known and used as one of the most powerful agents for producing the chemical operations desired by manufacturers. Heat of temperatures below the freezing-point, or cold, as it is commonly called, has been less generally employed, and enjoys less recognition as a force capable of practical application for production. It has been lately made to aid in the manufacture of Glauber's salt at some French works with such success as to suggest that its more general application is possible in other directions. Alum and copperas were formerly made from the pyretic shales of Rheims and Picardy, but the product from these sources has been driven from the market by the competition of other alums. A new process has been devised by M. Georges Fournier, of Paris, under which the lye from the oxidized shales, containing all of the aluminum sulphate and a portion of iron sulphate after a considerable part of the copperas has been deposited, is mixed with common salt in such proportion that there shall be sodium enough to combine with all the sulphuric acid, and chlorine enough to take up all the aluminum and iron. The mixed solution is then exposed to a temperature of from 3° to 5° below the freezing point, at which the sulphate of soda is almost insoluble. That substance is deposited in the ordinary form of Glauber's salts as a fine crystalline sediment, while the aluminum and iron remain in solution as chlorides. The "mother-liquor," or lye, is then run off, and the deposit is washed in brine cooled down to the freezing-point. After it is dried, it is fit for any purpose to which Glauber's salt is applicable. The mother-liquid which has been run off may be made into a chloride of aluminum, which is valuable for disinfecting purposes. A pure chloride of aluminum, suitable for use in dyeing, and for the destruction of the vegetable matter which is mingled with wool, may be prepared from cake-alum by a similar cold process. The results of the operation are, as before, a deposit of Glauber's salt and a solution of chloride of aluminum, but the latter substance is free from the admixture of iron. Another French inventor, by exposing the lyes of the "sal mixte" of the salt-works of the Mediterranean coast, consisting of common salt and sulphate of magnesia, to a temperature of about 11° below the freezing-point, obtains Glauber's salt in deposit with a solution of the chloride of magnesium, a substance largely used for weighting textile fabrics.


Fertility of Hybrids.—Mr. Darwin, in his "Origin of Species," has mentioned a case on the authority of Mr. Eyton, in which hybrids from the common goose and the Chinese goose were as fertile as among themselves. He has now reported in "Nature" concerning his success in raising birds from the eggs of a brother and sister from the same hatch of hybrids of these two species. Two trials were made: three birds were hatched from the first set of eggs, two others were fully formed but did not succeed in breaking through the shell, and the remaining eggs were unfertilized. From the second lot of eggs two birds were hatched. The