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Knight's Mechanical Encyclopedia (ed. Knight), C. (search)
he wedges, the pins in the open center of the latter preventing their falling out. Caoutchouc. Commonly called gum-elastic or india-rubber. A substance derived from the sap of various trees, of which the Jatropha elastica, called by the natives hevee, flourishing in the plains of Brazil, toward the lower part of the Amazon River, is the principal source of production. It was first brought to Europe in the early part of the eighteenth century, and fifty years later was mentioned by Dr. Priestly as a substance excellently adapted for removing pencil-marks from paper. Crumb of bread had previously been employed for this purpose. The sap, obtained by tapping the trees, is dried over a fire, which gives it the dark appearance observable in the rubber of commerce. For many years its various adaptabilities seemed unperceived, but in 1791 Samuel Peal obtained a patent for water-proofing fabrics by means of this gum dissolved in spirits of turpentine; though this does not seem to h
Knight's Mechanical Encyclopedia (ed. Knight), O. (search)
See also calcium-light; Drummond-light; oxyhydrogen light. Ox-y-ge-na′tor. A contrivance for throwing a stream of oxygen into the flame of a lamp. Oxycalcium-light. Ox′y-gengas Appara′tus. Oxygen gas was first discovered by Dr. Priestly August 1, 1774. Scheele and Lavoisier appear to have made the discovery independently very shortly afterward. Dr. Priestly first obtained the gas by heating red precipitate (red oxide of mercury, HgO) to a temperature of 752° Fah., by whicDr. Priestly first obtained the gas by heating red precipitate (red oxide of mercury, HgO) to a temperature of 752° Fah., by which the oxygen is expelled from this compund. Lavoisier verified the result by boiling mercury in a given quantity of air, thus forming red precipitate. Scheele obtained oxygen while engaged in experimenting upon some of the ores of manganese. It may be readily obtained by heating chlorate of potash, mixed with 1/3 or 1/4 its weight of black oxide of manganese, in a glass vessel to a temperature of 450° or 500° Fah., and collecting over a water-bath. This process is, however, rather expen