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POPULAR SCIENCE MONTHLY. 



of a gearing. A number of curved shelves 

 running longitudinally are fixed inside of the 

 cylinder. The iron may be in any conven- 

 ient 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 caus- 

 ing a constant falling of iron across the cur- 

 rent of the water. The effect upon the wa- 

 ter of the agitation with iron is simply to 

 cause a small quantity of iron, from one 

 tenth to one fifth of a grain per gallon, to be 

 dissolved. The water emerges from the pu- 

 rifier 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 fil- 

 ters, which are sand beds of ordinary con- 

 struction; through these filters the water 

 passes at the rate of from eighty to one hun- 

 dred 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 tol- 

 erably 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 hy- 

 drate insoluble compounds, so to speak, 

 which are removed from the water by settle- 

 ment 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 suffi- 

 ciently 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, deliver- 

 ing 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 suspen- 

 sion the whole of the iron oxide supplied to 

 it. This turbid water as it settles immedi- 

 ately 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 pres- 

 ent 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 con- 

 cave on the lower side, and each one is di- 

 vided 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 Lilien- 

 thal 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 ap- 

 paratus, had led him to practice in winds 



