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The pedagogical dictum, "from the concrete to the abstract," finds universal acceptance in this age of laboratory education. The idea of teaching through hand and eye in manual training is being put into practice more and more, owing to the great success that has been achieved by the pioneer institutions in this line. Why should not the same principles of co ordinate activity govern in the teaching of algebra? Can we not clear up some of the most troublesome points by making visual, concrete representations of negative numbers, and of equations? After covering an ebonite dish containing 0.03 gramme of radium bromide with an aluminium plate 0.1 millimeter in thickness, M. N. Orloff 'as noticed on the surface of the aluminium turned toward the radi um protuberances similar to small drops of melted metal, but not differing in appearance from that of the neighboring surface of aluminium. These protuber ances are radio-active and produce a photographic image through black paper in a few minutes. They appear to have emitted invisible radiations during a period of six months without noticeable abatement. The inference is that there is a formation of a stable alloy, due to the accumulation of particles proceeding from the atomic system of the radium around slight nuclei of aluminium. The Chemiker Zeitung describes the researches of Dr. H. Thorns on the obnoxious products of tobacco smoke, nicotine, and its products of decomposition, ammonia, methylamine, pyrrol, hydrogen sulphide, cyanhydric acid, butyric acid, carbonic acid, carbon oxide, watery vapor, pyrogenous essential oil, tarry and resinous products, among which the presence of a small quantity of phenol has been ascertained. He recommends the filtration of the smoke through cot ton soaked in ferric salts. The preparation is obtained by dissolving one part ammoniacal sulphate of iron in four parts of distilled water and 1-10 to 1-5 of a part of glycerine, soaking of the wadding and its desiccation, which ought to leave 50 per cent of the salt. By this process the fumes of the essential oil, of the hydrogen sulphide, the cyanhydric acid and about half of the nicotine and its products of decomposition, as well as the greater part of ammonia, are got rid of, while not depriving the smoke of its aroma. A Unique Process of Irrigation.—The Italian pro fessor, Cusmano, has originated a process which as sures an ample supply of water to plants growing in regions where the dry season is of long duration. Use is made of the Barbary nopal, the Opuntia vulgaris, a fig tree which is widely acclimated and bears figs that are excellent reservoirs of moisture. In spring a ditch, 30 centimeters deep and about 2 meters in di ameter, is dug at the foot of the tree that is to be protected from the drought. This ditch is filled with the figs cut into pieces about two fingers thick; to make a dense layer, they are beaten down and stems are added as the mass piles up. This mucilaginous pulp, covered with a layer of earth, stores up much water and gives it out gradually, thus watering the tree a long time. Prof. Cusmano asserts that after four months of drought he has found pulp still fresh, capable of supporting vegetation, and the foliage was in perfect condition. M. Berthelot has directed his researches to the white glass of ordinary test tubes, which commences to soften at 550 deg. C, and to the Jena glass, which softens only at 700 to 750 deg., and has communicated his conclusions to the Acad mie des Sciences. Glass kept for a long time at a temperature a little lower than its fusing point becomes opaque, and is devitrified. Softened silica is also at length modified. It is affected more rapidly when heated by the acetylene blowpipe, of which the temperature is sufllciently high for vola tilization. The permeability of glass as well as that of softened silica is like that of membranes manifest ing osmotic properties. It does not result from the existence of visible holes and fissures. The penetra tion especially occurs W6cn'*the silica and glass are softened by heat and thinned by a pressure of interior gases greater than that of the atmospheric pressure. The intervention of this permeability in the current phenomena of chemistry and physics has so far scarcely been suspected. Hereafter, the penetration or dissipation of gases, interior or exterior to vessels re garded as sealed, such as hydrogen, oxygen, nitrogen, helium, and the emanations of radio-active bodies, must be surmised whenever vessels of glass, silica, earthen ware, or porcelain, have been raised to a temperature near their point of softening, which occurs in organic analysis, in the reduction of metals by means of hydro gen, in the measurement of high temperatures by means of gas thermometers, and in tiio determinations of the density of vapors.
