Page:The American Cyclopædia (1879) Volume VI.djvu/81

DIAMAGNETISM oxygen of the air. "When air is passed through shavings of India rubber, the rubber retains a portion of the nitrogen, and the proportion of oxygen can be increased to 41 per cent. The proposition has also been made to separate substances which fuse at different temperatures by passing them through porous walls made of refractory material. This is called dialysis in the dry way. DIAMAGNETISM (Gr. Sia, through, and fiayvfj- TTJS, magnetic). In the native magnet (an ore of iron) resides a peculiar force, which, if a mass of this body be suspended freely, turns or directs it into a line nearly parallel with a meridian on the earth's surface, the same end of the magnet being always directed toward the north. Certain bodies, especially iron, brought near to a magnet, have the magnetic condition induced in them, the extremity near- er either magnetic pole becoming a pole of the opposite name, that more remote a pole of the same name. Small magnetizable particles, as iron filings, dusted upon a surface on which a magnet rests, or agitated near it, become arranged in lines which, between unlike poles that are presented to each other, run across in straight lines, while about those on either side they form curves, making larger and larger sweeps into space. The lines thus indicated have been named magnetic curves, or lines of force. Until recently the number of magnetic bodies was supposed to be very small. Bec- querel in 1827 found that a needle of wood playing freely on a pivot took a direction across, not in, the magnetic curves; and in 1829 Le Bailli also observed that bismuth repelled the magnetic needle. But the significance of these facts was not understood until Faraday in 1845, in the course of his experiments on magnetic rotary polarization, observed that a bar of so- called " heavy glass," suspended between the poles of an electro-magnet, moved, as soon as by the passage of the electrical current mag- netism was induced in the latter, into a posi- tion crossing the lines of force, or at right angles to the line joining the poles. Terming the position assumed by a soft iron bar, which is lengthwise between the two poles, or from one to the other, axial, Faraday gave to the new direction assumed by the glass the name of equatorial. The glass was not merely thus directed, it was repelled by either pole ; and if, reduced to the form of a small mass or cube, it was thrown out of the lines joining the poles to one side or the other, it moved into the position of weakest magnetic action. He also sealed up various liquids in long tubes of thin glass, and suspended them between the poles ; some arranged themselves axially, others equatorially. This new-found property of cer- tain bodies Faraday termed diamagnetism ; and in contrast with this he denominated the familiar form of magnetic action paramagnet- ism. His experiments warrant the conclusion that, with a sufficiently powerful electro-mag- net, all substances whatever can be shown to DIAMOND 73 exhibit one or other of these properties. (See MAGNETISM.) DIAMANTINA, a city of Brazil, in the province of Minas Geraes, capital of the ancient district of Tijuco, which was also formerly the name of the city, 270 m. N. of Rio de Janeiro ; lat. 18 28' S., Ion. 43 50' W. ; pop. about 7,000. The city is built in amphitheatre on a steep acclivity, 5,648 feet above sea level. The streets are irregular, and the pavement indif- ferent ; a few of the houses are fine, and the whitewashed walls of the others contrast pret- tily with the brilliant green foliage and golden fruit of the rows of orange and banana trees which surround almost every dwelling. Of the numerous churches some are handsome, especially the negro church dedicated to Nossa Senhora do Rozario, remarkable for a statue of a black Virgin surmounting the altar. Save in the public edifices, which are of stone, the building materials are mostly either mud or wood. There are three hospitals, barracks, a primary school, and a good market. Flowers, vegetables, and European fruits are cultivated in the gardens, of which one is attached to each house; and excellent water is supplied from crystalline springs. The inhabitants are mainly occupied in washing for gold and dia- monds, both of which abound in the surround- ing country. (See DIAMOND DISTRICT.) DIAMOND (a contraction of adamant, from Gr. a privative, da/uav, to subdue), a gem so named on account of its extreme hardness, for which, and its brilliancy and beautiful play of prismatic colors, it excels all others. The dia- mond is pure crystallized carbon, and has a spe- cific gravity slightly varying, according to the different qualities, as follows : Brazilian, color- less, 3-444; Brazilian, yellow, 3'519; oriental, colorless, 3'521 ; oriental, green, 3'524; oriental, blue, 3 '525. Its hardness, according to an artifi- cial standard scale, is 10, greater than that of any other known substance, that of corundum being 9, and that of quartz 7. The primitive form of the crystal, and that into which the sec- ondary forms may be converted by cleavage, is the regular octahedron. The faces of the crys- tals are often convex, and the edges curved. The cleavage planes greatly facilitate its cutting, and also present the most brilliant natural sur- faces. The gem is not acted upon by acids or alkalies, and when air is excluded may be heat- ed to whiteness without injury. When exposed to the heat of a powerful galvanic battery, it fuses and is converted into a mass resembling coke, its specific gravity being sometimes re- duced to 2-68. Its combustion may be effected in the open air or in oxygen gas, but it requires a very intense heat, which is scarcely estimable from the difficulty of using apparatus. Its combustibility was first proved by the Floren- tine academicians in 1694, by subjecting it to the solar rays concentrated in the focus of the large parabolic reflector made for Cosmo de' Medici, when it burned with a blue, lambent flame. The diamond is found in alluvial de-