Rensselaer Union, Volume 7, Number 43, Rensselaer, Jasper County, 15 July 1875 — MECHANICAL AND SCIENTIFIC. [ARTICLE]

MECHANICAL AND SCIENTIFIC.

—To solder German silver jx>ur out some spirits of salt into an earthenware or other dish, and put a piece of zinc in it. Then scrape the parts clean that are to Ik* soldered and paint over with the spirits of salt, .Next put a piece of pewter solder on the joint and apply the blow-pipes to it. Melt live parts of German silver and four parts of zinc into thin cakes, then powder it for solder.— Rural Neie Yorksr. —The experiment made by M. Proust, revealing the fact that fatly matters can be extracted from cast-iron when tbe latter is dissolved in certain acids, has lately been tested by M. Clocx. On lemming tlu*se materials in a pure state their analysis revealed the interesting fact that they eon sist of carburets of hydrogen of a certain series, and presenting the various terms thereof. This, it is stated, is a veritable organic synthesis, realized by the aid of substances purely mineral, and is susceptible, consequently, of important application. * ~ —An experiment illustrating the efficacy of dynamite in overcoming great resistances is described in a Belgian journal, the result lieing regarded as establishing quite conclusively the comparative safety, force aud economy of this explosive, as against gun-cotton. A large mass of east-iron, resulting from the leakage through the hot. tom of an iron smelting furnace, had on several occasions been subjected to the action of gunpowder, to break it up, but without success. The mass in question was about eight feet thick, and a number of cartridges of dynamite were introduced into one of the oid eliamliers which had been made when it was attempted to burst the mass by gunpowder. The result was to shatter the block into pieces, some of them being projected to a considerable distance. —The well-known susceptibility of hardened rubber to influences of temperature —expanding and contracting with great rapidity according to the varying degrees of heat and cold —Is now proposed to be made available in the construction of thermometers, somewhat on the principle of Breguet'B metallic thermometer. Two thin strips of rubber and ivory, eight inches long, glued or cemented together, will be flexed in one direction dr the other by elevation or depression of temperature above or below that at which they were originally joined. It one end lie fixed the other will move over a space of one or two tenths of an inch for a change of one degree centigrade. The expansibility of hard rubber being greater than that of mercury at ordinary temperatures, it is possible to construct a* mercurial thermometer with a bulb of this material, in which the column would rise with elevation of temperature and fall with depression.—X. Y. Sun. —The theory, so commonly accepted, in regard to the influence of forests on climate—especially that they encourage rain —lias lately lieeu the subject of considerable discussion among scientific men in Europe, the opinion being held by some that no such influence is exercised, and that it is more probable that rain is the cause of forests. Among the facts cited in thi* connection is the interesting -one furnished by districts in India in which the forest vegetation is just in proportion to the fgll of rain—being small and diminutive where there is but little rain, and abundant and gigantic where there is much—so that, though in temperate climates forests may produce an effect, they do not in the tropics. Several instances are also cited where there is much rain but a total absence of forests, and, on the other hand,' of thrifty forests where there is but little rain. It is probable, however, that the fact of forests not al ways growing in rainy districts arises from the waters accumulating and forming morasses in which forest trees would not grow; and in . districts where there is not mlicli rain there may be much moisture in the atmosphere. - • •