MAGNANIER

is the name given in the southern departments of France to the proprietor of a nursery in which silk-worms are reared upon the great scale, or to the manager of the establishment. The word is derived from magnans , which signifies silkworms in the language of the country people. See Silk . MAGNESIA (Eng. and Fr.; Bittererde , Talkerde , Germ.), is one of the primitive earths, first proved by Sir H. Davy to be the oxide of a metal, which he called magnesium . It is a fine, light, white powder, without taste or smell, which requires 5150 parts of cold water, and no le than 36,000 parts of boiling water, for its solution. Its specific gravity is 2·3. It is fusible only by the heat of the hydroxy gen blowpipe. A natural hydrate is said to exist which contains 30 per cent. of water. Magnesia changes the purple infusion of red cabbage to a bright green. It attracts carbonic acid from the air, but much more slowly than quicklime. It consists of 61·21 parts of metallic basis, and 38·79 of oxygen; and has, therefore, 20 for its prime equivalent upon the hydrogen scale. Its only employment in the arts is for the purification of fine oil, in the preparation of varnish. Magnesia may be obtained by precipitation with potash or soda, from its sulphate, commonly called Epsom salt; but it is usually procured by calcining the artificial or natural carbonate. The former is, properly speaking, a sub carbonate, consisting of 44·69 magnesia, 35·86 carbonic acid, and 19·45 water. It is prepared by adding to the solution of the sulphate, or the muriate (the bittern of sea-salt evaporation works), a solution of carbonate of soda, or of carbonate of ammonia distilled from bones in iron cylinders. The sulphate of magnesia is generally made by acting upon magnesian limestone with somewhat dilute sulphuric acid. The sulphate of lime precipitates, while the sulphate of magnesia remains in solution, and may be made to crystallize in quadrangular prisms, by suitable evaporation and slow cooling. Where muriatic acid may be had in profusion for the trouble of collecting it, as in the soda works in which sea salt is decomposed by sulphuric acid, the magnesian limestone should be first acted upon with as much of the former acid as will di olve out the lime, and then, the residuum being treated with the latter acid, will afford a sulphate at the cheapest po ible rate; from which magnesia and all its other preparations may be readily made. Or, if the equivalent quantity of calcined magnesian limestone be boiled for some time in bittern, the lime of the former will displace the magnesia from the muriatic acid of the latter. This is the most economical proce for manufacturing magnesia. The sub carbonate, or magnesia alba of the apothecary, has been proposed by Mr. E. Davy to be added by the baker to damaged flour, to counteract its acescency. MAGNESIAN LIMESTONE ( Dolomie , Fr.; Bitter talk , Talks path , Germ.), is a mineral which crystallizes in the rhombohedral system. Spec. grav. 2·86; scratches calc-spar; does not fall spontaneously into powder, when calcined, as common limestone does. It consists of 1 prime equivalent of carbonate of lime = 50, a ociated with 1 of carbonate of magnesia = 42. Ma ive magnesian limestone , is yellowish-brown, cream-yellow, and yellowish-gray; brittle. It di olves slowly and with feeble effervescence in dilute muriatic acid; whence it is called Calcaire lent dolomie by the French mineralogists. Specific gravity 2·6 to 2·7. Near Sunder land, it is found in flexible slabs. The principal range of hills composing this geological formation in England, extends from Sunder land on the northeast coast to Nottingham, and its beds are described as being about 300 feet thick on the east of the coal field in Derby shire, which is near its southern extremity. On the western side of the Cumber land mountains magnesian limestone overlies the coal measures near White haven. The stratification of this rock is very distinct, the individual courses of stone not exceeding in general the thickne of a common brick. The lime resulting from the calcination of magnesian limestone appears to have an injurious action on vegetation, unle applied in quantities considerably le than common lime, when it is found to fertilize the soil. After two years, its hurtful influence on the ground seems to become exhausted, even when used in undue quantity. Great quantities of it are annually brought from Sunder land to Scotland by the Fifes hire farmers, and employed beneficially by them, as a manure, in preference to other kinds of lime. It has been unfairly denounced by Mr. Tennent and Sir H. Davy, as a sterilizer. This rock is used in many places for building; indeed our most splendid monument of Gothic architecture, York Minster, is constructed of magnesian limestone.