SCIENTIFIC AND USEFUL.

New Zealand Graphic, Volume XII, Issue XVII, 28 April 1894, Page 392

SCIENTIFIC AND USEFUL.

attacked by steam. According to Krupp, coal, etc., is very readily attacked by steam when it has been previously moistened with a solution of an alkali, or of the carbonate of an alkali, the reaction in that case occurring at relatively low temperatures. The products are almost exclusively carbonic acid and hydrogen, and carbonic oxide is hardly present at all if the walls of the retort are of fire brick : for there is then no iron to effect any reduction. It is said that by passing this mixture over lime, etc., pure hydrogen is produced, and the carbonic acid can be recovered from the absorbing lime employed and dealt with by itself as pure artificial carbonic acid, the lime being also recovered by this means. MOVING CAGES IN MINING SHAFTS. Opinions are generally agreed as to the advisability, if not the absolute necessity, of establishing simple,'trustworthy, and permanent means of communication between men in the moving cage in mine shafts and the engineman on the suiface. Herr Otto Winkler, of Dresden, has, we learn, solved the question in a very practical manner. His invention, we hear, was awarded a gold medal at the competition of apparatus for improving the position of workmen, at Cologne, in 1890. Herr Winkler has received favourable reports as to the working of his signal from the Konigliche Berg-Inspektion, Dresden, the Zwickan Colliery Company, the Hauichener Bergwerks Direktion, and other mining bodies. WANTED MECHANICAL INGENUITY. There is an opening for mechanical ingenuity in the direction of the street paving of Trieste, according to a recently issued Foreign Office report. At present the whole of this large town is paved with solid blocks of limestone of great massivemess and weight. The blocks are laid down close together, and are from three to six feet long by fifteen inches wide, and the same deep. Owing to the great size and flatness of these stones, it is necessary from time to time to rough them by band, in order to afford foothold for animals, this work being pei formed by gangs of men armed with mallet and chisel. The process is exceedingly slow, the labour and expense considerable, the waste of stone very great, and the work is, moreover, attended with danger to passers-by from the sharp chips which fly in every direction. It would seem that what is required is a light portable machine, with engine, to travel and chip the stones at speed, somewhat, perhaps, after the system ot the stamps used in ore crushing, but placed in a slanting position. FILTERING WATER. The growing realization of the value of pure water has brought about a great many improvements in our filtering apparatus. A new system has recently been introduced by Mr C. H. Fitzmaurice, of Shepperton, by which impure water, or other liquid, is first thoroughly mixed in a vessel provided with an agitator, with caustic lime or some other softening material, and then pumped up through a vessel filled with pottery tiles or wood, which serve to arrest all flocculent matters. At the top'of this latter vessel are two perforated plates, between which a thick layer of cocoanut fibre, yarn, or other material is placed, and through which the water passes. This invention can be adapted to ordinary cisterns by employing a tray carrying a series of partially-glazed'jars. arranged in zig-zag, in which the softening material is placed. The object of partially glazing the jars is to allow the softening agent to be saturated, and to mix gradually with the impure water. After passing into the tray and through the jars, the water overflows into the tank, either through the perforations or over the tray. WHAT SMOKE CONSISTS OF. Smoke consists of minute particles of solid or liquid matter suspended in the air, and its colour depends partly upon the chemical constituents of such particles, but also largely upon their size. Exact experiment has shown that as the size of minute particles suspended in air is gradually increased they rise to colour varying from sky blue down through the whole range of the spectral scale. This is the cause of sunset and sunrise colours in the sky. Its effects can be traced in the case of the two kinds of tobacco smoke, modified by the murky tints of the carbonaceous products. The smoke given off from the heated surface of the burning tobacco in the bowl of the pipe consists of matter, all of which has been highly heated and very fully oxidized and decomposed. It consists mainly of exceedingly small solid particles, exhibiting by virtue of their smallness a bluish colour. On the other hand, that smoke which has been drawn through the tobacco into the mouth of the smoker carries with it a relatively large quantity of water and hydrocarbon, which are condensed upon the solid particles above mentioned. The relatively large size of such particles explains the well-known greyish-colour of the smoke which issues from the mouth of the smoker.