Text: In 1778 Brugmans of Leyden observed that when a lump of bismuth was held near either pole of a magnet needle it repelled it. In 1827 Le Baillif and Becquerel observed that the metal antimony also could repel and be repelled by the pole of a magnet. In 1845 Faraday, using powerful electromagnets, examined the magnetic properties of a large number of substances, and found that whilst a great many are, like iron, attracted to a magnet, others are feebly repelled. To distinquish between these two classes of bodies, he termed those which are attracted PARAMAGNETIC (or simply MAGNETIC, some authorities us the term FERRO-MAGNETIC), and those which are repelled DIAMAGNETIC. The property of being thus apparently repelled from a magnet he termed DIAMAGNETISM. Faraday's methods of experiment consisted in suspending a small bar of the substance in a powerful magnetic field between the two poles of an electromagnet, and observing whether the small bar was attracted into an axial position with its length along the line joining the two poles, or whether it was repelled into an equatorial position, at right angles to the line joining the poles, across the lines of force of the field, suspended between the poles of an electromagnet constructed on Ruhmkorff's pattern. The following are the principal substances examined by the method: cm=Km-1 (x 10-5) PARAMAGNETIC DIAMAGNETIC Aluminum 2.2 Ammonia -1.06 Sodium 0.72 Carbon (diamond) -2.1 Iron 66 Bismuth -16.6 Nickel Phosphorus Cobalt Antimony Manganese Thallium Chromium Zinc Cerium Mercury -2.9 Titanium Lead -1.8 Platinum 26 Platinum (pure) Many ores and salts containing Silver -2.6 the above metals Copper -0.92 Oxygen gas 0.19 Gold Oxygen liquid Water -0.90 Ozone Tellerium Tungsten 2.4 10^-5 Alcohol Uranium 40 Sulphur Hydrogen -0.00022 Silicon -0.37 Ion Estimated Diamagnetic Susceptibility Li+ -1.825 Na+ -8.225 K+ -15.925 Rb+ -23.675 Cs+ -34.8 F- -8.6 Cl- -22.6 Br- -32.9 I- -47.7 Ion Estimated Diamagnetic Susceptibility Susceptibility Mg++ -7.375 Ca++ -10.475 Sr++ -18.8 Ba++ -29 Liquids were placed in glass vessels amd suspended between the poles of the electromagnet. Almost all liquids are diamagnetic, except solutions of salts of the magnetic metals, some of which are feebly magnetic; but blood is diamagnetic though it contains iron. To examine gases bubbles are blown with them, and watched as to whether they were drawn into or pushed out of the field. Oxygen gas was found to be magnetic; ozone has been found to be still more strongly so. Dewar has found liquid oxygen sufficiently magnetic to rush in drops to the poles of a powerful magnet. The diamagnetic properties of substances may be numerically expressed in terms of their permeability or their susceptibility. For diamagnetic bodies the permeability is less than unity. For bismuth the value of u is 0.999969. The repulsion of bismuth is immensely feebler than the attraction of iron. Plucker estimated the relative magnetic powers of equal weights of substances as follows: Iron + 1,000,000 Lodestone Ore + 402,270 Ferric Sulphate + 1,100 Ferrose Sulphate + 780 Water - 7.8 Bismuth - 23.6 It is found that feebly magnetic bodies behave as if they were diamagnetic when suspended in a more highly magnetic fluid. A small glass tube filled with a weak solution of ferric chloride, when suspended in air between the poles of an electromagnet, points axially, or is paramagnetic; but if it be surrounded by a stronger (and therefore more magnetic) solution of the same substance, it points equatorially, and is apparently repelled like diamagnetic bodies. All that the equatorial pointing of a body proves then is, that it is less magnetic than the medium that fills the surrounding space. A ballon, though it possesses mass and weight, rises through the air in obedience to the law of gravity, because the medium surrounding it is more attracted than it is. But it is found that diamagnetic repulsion takes place even in a vacuum: hence it would appear that the ether of space itself is more magnetic than the substances classed as diamagnetic.

See Also: PARAMAGNETISM; OXYGEN

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