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Page:Popular Science Monthly Volume 21.djvu/582

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568
THE POPULAR SCIENCE MONTHLY.

Œningen in Switzerland, Radoboj in Hungary, Monte Balca in Italy, and the Florissant basin in Colorado, are celebrated for the rich harvests of insects they afford. The nature of the deposits seems to have exercised some influence upon the greater or less frequency of certain types, for each of these beds is distinguished by the prevalence of particular types. Elytræ are found in quaternary beds, which have largely preserved their metallic luster. A curculio-form found in England has a tropical grandeur of size. Most of the later fossil species on the Continent are identical with those now living in Europe. Fossil insects present but few of those strange gigantic forms that astonish us among the other classes of animal remains. The largest and most curious forms found are still surpassed in tropical countries. The insects which occur in the Lias, among the remains of monstrous pterodactyls and extinct saurians, are all of families that are still represented in life; and the oldest insects of the Devonian could be inserted among living Orthoptera without disturbing the symmetry of the order.

 

Sewage-Irrigation in German Cities.—M. Durand-Claye, a sanitary engineer of Paris, has published a report on the systems which are employed in the German cities of Dantzic, Berlin, and Breslau, for the final disposal of sewer-water. The systems of filtering and of precipitation by chemical agents were tried, but were found not to effect a sufficient purification; and irrigation was finally chosen as furnishing on the whole the most economical and satisfactory method. The water is cleansed of its grosser solids before being pumped up from the sewers; it is afterward conducted to the irrigated tracts. At Dantzic, the sewage is turned upon a tract of about twelve hundred and fifty acres of a sandy, arid soil, and is led around beds devoted to the culture of garden vegetables. The surplus water, which is drained off to the Vistula, has been proved to have lost seven eighths of its organic matter, five sixths of its ammonia, and one half of its mineral impurities. The ground has an excessive absorbing power, and it has been necessary to box the main conduits to have any water left for the smaller irrigating channels. Thus far, four hundred and seventeen acres have been enough to absorb all the sewage of the city, indicating an absorbing power of thirty-two thousand cubic metres a year for each acre. The works have been made and are kept up without cost to the city, for the use of the irrigated lands for thirty years; and the land is sublet to gardeners for from twenty to twenty-eight dollars an acre. The mortality of the city—one of about one hundred thousand inhabitants—has been reduced twenty-one per cent under the operation of this system. At Berlin, after some unsatisfactory experiments with chemical agents, irrigation was tried on about fifteen acres of land. The tract took in and purified 231·618 cubic metres of water in a year and nine months, and returned good crops. The municipality determined to treat all of its sewer-waters in the same way, and bought two tracts, one of seventeen hundred and forty acres, the other, at Osdorf and Friederickenhof, of two thousand and sixty acres. One thousand and eighty acres of the latter tract only have been used. In addition to the cultivated plats, drained basins are provided for the water that is not needed on the crops, in which, after a deposit about a foot thick has accumulated, the ground is dried, dug up, and made ready for cultivation in the next year. The waters thus treated cease to give off odors and lose all unhygienic properties; the health of the workmen and the comfortable occupation of the neighboring country seats are not affected by them. The cost of managing the lands is defrayed by the sale of products, so that the city is only at the expense of pumping up the water, while it is able to let the lands at from twenty-four to thirty-four dollars an acre. The city of Breslau uses a tract of about twelve hundred acres, of such a character that extra drainage is necessary. The irrigated lands are let to the engineer who constructed the works at a scale of rents which is to rise in four years to eighteen dollars an acre.

 

The Salt Deposits of the Persian Gulf.—On the eastern side of the Persian Gulf is an extensive area containing a large deposit of salt which crops out at various