A dictionary of chemistry, on the basis of Mr. Nicholson's: in which the principles of the science are investigated anew, and its applications to the phenomena of nature, medicine, mineralogy, agriculture, and manufactures, detailed (Volume 2).

  • Ure, Andrew, 1778-1857.
Date:
1821
Catalogue details

Licence: Public Domain Mark

Credit: A dictionary of chemistry, on the basis of Mr. Nicholson's: in which the principles of the science are investigated anew, and its applications to the phenomena of nature, medicine, mineralogy, agriculture, and manufactures, detailed (Volume 2). Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    The thicknesses corresponding to the dif- ferent summits, are to each other, as the lengths of their respective axes. 2. Were the atmosphere, and the glass support, perfect non-conductors, the above distribution would continue till some other body was brought near to, or in contact with, the ball. But the surface of even lackered glass, yields slowly to the idio-re- pulsive power of the electrical fluid; and the atmosphere, partly by its aqueous par- ticles, and partly by its own feebly con- ducting power, continually robs the globe of its electricity. The immediate aerial envelope no sooner acquires electric im- pregnation, than it recedes, and is repla- ced by a new sphere of gaseous particles. By this intestine aerial movement of re- pulsion and attraction, the ball, in a short time, loses its excess of vitreous or resin- ous electricity, and resumes the neutral state. By placing it in the centre of a dry glass receiver, the period of electrization may be prolonged, but, sooner or later, the electric equilibrium is restored be- tween it, and the surrounding matter. 3. If we bring into contact with the above electrized ball, an unelectrified one of the same bulk, but of a very different weight, we shall find an equal distribution to take place between them. An insula- ted disc or spherule applied to the surface of each, will be capable of affecting a gra- duated electrometer of torsion, to the same degree. We thus perceive that bo- dies do not act on electricity, by any spe- cies of elective attraction or affinity. They must be regarded n:erely as vessels, in which this power is distributed, agree- able to the laws of mechanics. When the aboTe globes are separated, their electricities diffuse themselves uni- formly about them, and the quantities are found equal when the surfaces are so. But if the surfaces be unequal in any given ra- tio, it then happens that the quantity of electricity varies in a different ratio, which is less than that of the surf ces. Thus Coulomb ascertained, that when the sur- face of the smaller globe was nearly one- fifteenth of that of the larger, its quantity of electric fluid was one-eleventh. The following is his general table of results:— ., , -ci Density in little sphere, Surface of Sphere. whJsurface L L 1 1 4 1.08 16 1.30 64 1.65 Infinite, less than 2.00 Do. calculated by M. Foissor, 1.65 The difference therefore can never amount to two. He placed two globes, each of two inches diameter, in a line with a globe of eight inches diameter; the two smaller ones being in contact, and one of them with the larger. He found that the quantity of electricity of the smaller globe, most distant from the greater, was to that of the intermediate, as 2.54 to 1. Four globes of two inches being placed in a row, successively in contact with each other, and with a globe of eight inches diameter, the ratio of the quantities of electricity taken by the small globe, farthest from the large one, and that nearest it, was found to be 3.4 to 1. Having placed 24 globes, each of two inches diameter, in a like series with the larger globe, Coulomb compared the 24th little globe, that is to say, the last in the row, with others in the same row, and the results were as follow:— 24th to the 23d as 1.49 to 1 24th to the 12th as 1.7 to I 24th to the 10th as 2.1 to 1 24th to the 1st which was in contact with the large globe, as 3.72 to 1 2^lh to that of the large globe, as 2.16 to 1. When two electrified spheres, of equal size in contact, are examined as to the state of the electricity on the different points of their surfaces, we have the following rela- tions:— Position of the points Ratio of the second compared. thickness to the first. 90° and 20° insensible 90 30 0.2083 90 60 0.7994 90 90 1.0000 90 180 1.0576 If the diameters of the two globes be as 2 to 1. 90* and 30° insensible 90 60 0.5882 90 90 1.0000 90 180 13333 That in ordinary cases, electricity is ct n- fined on the surfaces of bodies, not merely by the non-conducting faculty of the air, but by a species of mechanical pressure which air exercises, becomes evident, when we lessen the density of the air by exhaus- tion. Though the conducting aerial par- ticles are thus greatly diminished in num- ber, rendering the insulation apparently more complete, yet the electric power now emanates with vast rapidity, from the elec- trized ball, in visible coruscations Rare- fied air is therefore a good conductor. 4. By touching various points of insula- ted electrized bodies with a Rule disc of metallic foil, cemented to the end of a nee- dle of lac, which he applied to Itis electro- meter, M. Coulomb ascertained (he varia- tion of electrical density, that exists at dif- ferent points on the surfaces of bodies, of different forms and magnitudes. He thus