Rensselaer Union, Volume 7, Number 47, Rensselaer, Jasper County, 12 August 1875 — MECHANICAL AND SCIENTIFIC. [ARTICLE]

MECHANICAL AND SCIENTIFIC.

—ln stamping sheet zinc in dies much waste occurs from a small difference between the melting point and the temperature at which sheet zinc should tie stamped to get the best effect. To obviate this waste heat the zinc by dipping in oil at the proper temperature. —Scientific American. —Two specimens of mites have been found flourishing in theskinof the human face. One, the Aearopsis Mericourti, was discovered in the pimples on the face of a French officer who had been in Havaiia, Cuba. A similar species was taken from the skin of the nose of a person in New Orleans. Mr. Macalister recently exh,\b-' ited to the Dublin Microscopical Club twb specimens of a species of mite that had been taken from the face of a lady in Jamaica. They were male and female and apparently new to science. —Spirit having the specific gravity .92 at sixty degrees Fahrenheit is called proof spirit; that which is heavier is said to be under proof, while that which is lighter is called over proof. The origin of these terms is as follows: Formerly a very rude mode of ascertaining the strength of spirits was practiced, called the proof. The spirit was poured upon gunpowder in a dish and inflamed. If at the end of the combustion the gunpowder took fire the spirit was said to be above or over proof; but if the spirit contained much water the powder was rendered so moist that it did not take fire; in this case the spirit was declared to be below or under proof. —A very valuable plastic material has been introduced in Paris, the constituents of which are gutta-percha, oxide of zinc, amianthus and sulphate of baryta, in conjunction with various colors. The guttapercha is first prepared and bleached by being dissolved in rectified naphtha, benzole," or sulphuret of carbon, and when the compound does not exhibit sufficient elasticity, caoutchouc is added. After the gutta-percha is prepared and filtration effected the solution is placed in a still, the other ingredients are added, and the whole well stirred together. Heat is then applied until all the volatile oil is driven offf-when the material is removed to the desired mold§. It is said to be suitable for quite a variety of molded works of art, tissues, or artificial flowers, and when rolled into sheets forms a substitute for leather in certain cases. —Prof. Duncan, one of the ablest among European astronomers, has lately declared that there is strong evidence that the earth is a solid body now cooling, because the deeper the penetration into mines, or of boring into the earth, the hotter is the temperature; and if the temperature continues to increase at depths to which man cannot reach in the same ratio that it does at depths to which he can reach, a temperature of 3,680 degrees would be found at a depth of forty-five miles. At this temperature granites and lavas fuse. Assuming, then, says Prof. Duncan, the earth to be a hot body now cooling, as it cools the rocks must contract—.moreover, those rocks which are rich in silica will not contract so rapidly on cooling as others, and consequently herein is a source of change in the shape of the earth. Prof. Duncan says it is well known that surface changes are going on; that some large areas of land are in course of slow rising, while otliers are slowly sinking, and that at one geological period there was a great upheaval of the larger portion of the continent of North America. He concludes, therefore, that the globe is cooling unequally; the radiation, too, from some parts is greater than at others, and in this there is consequently a further source of disturbance.