XXXIV. On the presence of Magnesia in rocks

Abstract

Magnesia enters largely into the composition of the crust of the earth. As chloride and sulphate, we find it in sea, river, and spring water; in some cases it occurs in considerable quantity. In the Dead Sea, Th. T. & W. Herapath found 7.822 per cent., and Booth and Muckle as much as 14.590 per cent. of magnesium chloride. Some of the brine pools of Russia contain even a much higher per centage. Carbonate of Magnesia is found in pretty considerable quantities in Greece; but it occurs more frequently in combination with carbonate of lime, as dolomite or magnesian limestone, one of the most durable of our building stones when properly selected. Silicate of Magnesia is a constant ingredient of such rocks as hornblende, olivine, asbestos, &c. Magnesium is a brilliant silver-white metal, somewhat brittle at the ordinary temperature; at a red heat it melts, and burns with a brilliant white light, which is available for photographic purposes, and, by its agency, Professor C. Piazzi Smyth is at present engaged in taking photographs of the interior of the Pyramids. It was first separated from magnesia by Sir H. Davy in 1808, but produced only as a mere chemical curiosity till 1863, when Mr. E. Sonstadt secured a patent for its manufacture in large quantities at a comparatively moderate cost. The white powder produced by the combustion of the metal is the oxide, or magnesia. It is generally seen as a white powder sparingly soluble in water; it occurs naturally as This 250-word extract was created in the absence of an abstract