Rensselaer Union, Volume 7, Number 49, Rensselaer, Jasper County, 26 August 1875 — MECHANICAL AND SCIENTIFIC. [ARTICLE]

MECHANICAL AND SCIENTIFIC.

—The best and most durable insulation for electric wires is to tliin them and cover with pure rubber.— Scuiitifir Anu riMn. < —A Frenchman namtsl Georges has been for many years experimenting ornthe preservation of fish. At length he has invented a fluid which appears to be fexact- ; ly what is desired. Various kinds of fish were placed in a bath ot the solution for two hours, then put in a cellar, and after six days were found *in a state of perfect ■ preservation. Both flavor and color were : perfect. This invention is believed to la* ! of great value. —The following is a simple mode of rendering water almost as cold as ice ; without the use of ice: J>t the jar, pitch- , er or vessel used for water be surrounded with one or more folds of coarse cotton kept constantly wet. The evaporation of the water will carry off the heat from the inside and reduce h to a freezing point. In India and other tropical regions whereice cannot be produced this method of proceeding is common. —M. Malassez has contrived an instrument which is said to be superior to those previously used for ascertaining the number of red corpuscles in a given amount of blood. It consists of a capillary tube, into which artificial serum is introduced, and which is graduated so that the contents of a given length are known. The mean number of red corpuscles in human blood is discovered to be 4,000,000 in each cubic millimetre. A greater number is-found in smaller arteries, and most in the veins that have lost part of their serum by exosmose. They arc fewer in cases of cancer and tuberculose. Lead poisoning also lessens their number. —According to M. Sonstadt, the seawater of the British coasts contains,in solution, besides silver, an appreciable quantity of gold—estimated at about one grain to a ton of water. This is separable by the addition of chloride of barium, apparently as an aurate of baryta adhering to the precipitated sulphate, which yields, by assay, an alloy of about six parts of gold to four of copper. Other methods have also been devised by chemical ingenuity for separating the metals in question from their solution in sea-water, but not, of course, in a manner or to an extent rendering it a practical object. The agent which keeps the gold of the sea in a soluble and oxidized condition is, according to M. Sonstadt, simply the iodine liberated under certain conditions.

—That glass is practically a non-con-ductor of heat as well as of electricity has been demonstrated by various ingenious experiments. A familiar example in foint is the use of glass as an insulator, a non-conductor for telegraphic purposes. It is difficult to draw the line of non-con-duction, but bad conductors of heat are practically assumed as non-conductors. The question of conduction is simply one of degree. Thus, let twe rods of equal size and length —but one of copper and the other of glass—be brought together, and have at their extremity a small weight or marble attached by wax; then apply a spirit lamp to their ends, touching each other so that the heat be equally applied. Now, in the copper, owing to its being a gtxxi conductor, the wax will rapidly melt and let the weight drop; while in the case of the glass, owing to its being a very bad conductor, a long time must i elapse before such a result can ensue. —The fact that tinned surfaces often contain lead as an adulteration in sufficient quantities to act injuriously upon •acid solutions of vegetables, fruit, etc., which are brought hi contact with them is well known, and certain Wise counselors do not hesitate to protest against the general use of these canned fruits, which are put up in tin instead of glass cans. Since, however, nothing less than an astounding wholesale catastrophe is likely to induce a public abandoment of this class of luxuries, it may be of sen ice to name a simple method by which the presence of acid can be detected, and thus the manufacturer be compelled to furnish a purer material. Having cleaned the suspected surface thoroughly place upon it a drop or thin coating of nitric acid. Through the chemical reaction thus induced stannic oxide is formed and nitrate of lead, if this metal be present After a few moments the acid should be expelled by means of gentle heating; the pulverulent spot produced by the acid should then be treated with a solution composed of five parts of iodide of {jotassium in 100 parts of water. Should ead lie present this treatment will result in the formation of yellow iodide of lead, which may be readily detected by its characteristiccolor, since the iodide has no action upon the pure oxide of tin.—-Ex-change.