Page:Popular Science Monthly Volume 49.djvu/154

142 of a gearing. A number of curved shelves running longitudinally are fixed inside of the cylinder. The iron may be in any convenient form, but the most commonly employed in practice is the burrs or punchings from plates. The charge varies, of course, with the size of the cylinder, a purifier capable of treating a million gallons of water in twenty-four hours requiring about two tons. When the machine is set in motion, the curved shelves scoop up the charge of iron and shower it down through the water, thus causing a constant falling of iron across the current of the water. The effect upon the water of the agitation with iron is simply to cause a email quantity of iron, from one tenth to one fifth of a grain per gallon, to be dissolved. The water emerges from the purifier and passes to settling tanks, where the ferrous hydrate, which has been formed, is oxidized into ferric hydrate, and settles to the bottom of the tank. From the settling arrangement the water passes on to the filters, which are sand beds of ordinary construction; through these filters the water passes at the rate of from eighty to one hundred gallons per square foot per twenty-four hours, and emerges pure and free from any trace of iron. It was formerly considered that the iron had a more or less pronounced chemical action upon the dissolved organic impurities of the water; the oxide formed was considered to act as a carrier of oxygen, by means of which the organic matters were actually burned up and destroyed. It is tolerably certain now, however, that the real action is one of coagulation; the formation of a precipitate in the water tending to throw out of solution the dissolved organic substances, which form with the ferric hydrate insoluble compounds, so to speak, which are removed from the water by settlement and filtration. This view of the action of the iron upon the organic impurities of a water applies equally well to its action upon microbes. The germs are entangled in the gelatinous precipitate, and either subside with it to the bottom of the settling tank, or remain behind on the surface of the filter. Moreover, the film of oxide which covers the surface of the sand appears to act like a Chamberland-Pasteur filter, retaining the microbes while allowing the water to pass freely. A very important feature of the iron process consists in the rapidity with which perfect results are secured. A sand filter of ordinary construction will remove a very large proportion of the microbes in a water when its surface has become sufficiently blocked by the layer of matter, living and dead, separated from the water being filtered. To obtain this result, however, it is necessary to work the filter for days, delivering all the while imperfectly filtered water, until this layer has time to form. With the iron process, however, no such thing occurs. The practice is, when a filter is restarted after cleaning, to refill it from below with purified water from another filter until the surface of the sand is submerged; and then to admit from above water direct from the outlet of the purifiers, containing in suspension the whole of the iron oxide supplied to it. This turbid water as it settles immediately forms the desired film. Then the filter is set to work, and yields, from the first, water containing the minimum number of germs. The film thus formed is quite clean, and is never slimy or offensive.

Recent Experiments in Flying.—In an interesting article in Nature describing and picturing the flying appliances of Herr Otto Lilienthal, who has been experimenting for some time past near Berlin, it is said that his experiments "have from the very beginning been rewarded with a distinct success; and it seems that, given time, he may present us if not with a method of flying, then with an approximation to it, which perhaps at some later date may be more fully developed." He has already succeeded in making fairly long flights with perfect safety. His present apparatus consists of two parallel planes one above the other, the upper being about three fourths of a wing breadth above the lower. Each plane has an area of nine square metres. The planes are slightly concave on the lower side, and each one is divided into two wings by a fore-and-aft hinge. There are two rudders at right angles to each other fastened to the rear end of the lower plane. With this new apparatus Herr Lilienthal has already found that a step in the right direction has been made. The energetic movement of the center of gravity, and the consequent more safe management of the apparatus, had led him to practice in winds