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 metals having1 the strongest attrac- tion for oxygen, are the metals which form the positive pole, in all cases in which the fluid menstrua act chemically, by affording oxygen; but when the fluid menstrua af- ford sulphur to the metals, the metal having the strongest attraction for sulphur, under the existing circumstances, deter- mines the positive pole. Thus, in a series of copper and iron, introduced into a por- celain trough, the cells of which are filled with water, or with acid solutions, the iron is positive, and the copper negative; but when the cells are filled with solutions of sulphur and potash, the copper is positive, and the iron negative. In all combinations in which one metal is concerned, the surface opposite the acid is negative, while that in contact With the solution of alkali and sulphur, or of alkali, is positive. Every one who has a perception of the beautiful in philosophical research, must regard this important law, discovered by Sir H Davy, with admiration. It promises to lead us eventually into the mysteries of electro-chemical action, further than any general principle hitherto established. It gives another fine analogy between elec- tricity and heat. For as the disengagement of the latter power is always proportional to the intensity of chemical combination, so in the present case we see, that the in- tenser chemical action is connected with the evolution of positive eiectricuy, while the feebler is associated with the negative. The positive electricity, if we judge from the appearance of its light, is the more ac- tive of the two; and it is known to promote the most intense combinations of bodies, viz. those with chlorine, iodine, and oxy- gen. The divergence of the leaves in the gold- leaf electroscope, and more exactly, the separation of the ball and disc in the elec- trometer of Coulomb, are proportional to the resilient force, or intensity of the elec- trical agent. Hence the repetition of a se- ries of moderate sized voltaic plates, indi- cates the same repulsing energy on these instruments, as the same series of much larger plates. With regard to imperfect conductors, like the human body, or nen- trosaline solutions, the effects, namely, the shock, and transfer of the elements, are al- so proportional to the electrical intensity, or electroscopic indications. For these pur- poses, we need not enlarge the plates be- yond a certain size, which is relative to the conducting power of the substances, through which the electrical energy is to be transmitted. But with excellent con- ductors, like charcoal and the metals, the quantity of electricity, and not its slate of condensation, is to be regarded. The in- tensity is essential, to enable it to commu- nicate electrical polarities to a series of material liquid molecules, or to force its way, so to speak, through the animal frame. But the same intensity is altogether su- perfluous relative to metallic objects. To operate changes on these, we must favour the evolution of a great mass of electri- cal power, by using plates of extensive areas. To prove the justness of these views, let us bring into action, by the same exciting liqu.d, a clean battery of 20 pairs of 1 inch, and 2u pairs of lu inch plates. On expos- ing a small column of water, in a glass tube, first to the one battery, and then to the other, or on connecting, with the two hands, first the extremities of th one, and then those of the other, we shall perceive the evolution of gases, or the shock, to be nearly equal. While the energy of the larger battery is acting on the water or hu- man body, let two little cylinders, of char- coal, connected with the ends of the trough by metallic wires, be made to touch each other, the electrical excess will be suffi- cient to produce vivid ignition at the points of contact. Silver leaf may be substitu- ted for the charcoal, with a simi'ar effect. The little battery, however, e:\hausts its energy on the column of water. When thus employed, it will give scarcely any sensation to the finders, ai d produce no effect on the charcoal or leaf. l£\en the battery of Mr. Children, which, after ig- nitin. great lengths of platinum wire, to a whiteness insupportable to the eye, fused it into globules; and which emitted from charcoal a light more dazzling than the sunbeam, had no more effect on water, and the living body, than an equal series of little plates. As Mr. Children's battery is the most powerful in the world, in calorific effect, so that of 2J00 pairs of [dates, of 32 inches e.ich, furnished by the subscription of a few patrons of science connected with the Royal Institution, is the most powerful yet constructed in electro-chemical intensity. The whole surface is 128000 square inches. This battery, when the cells were filled with 60 parts of water, mixed with one part of nitric acid, and one of sulphuric acid, afforded a series of brilliant and im- pressive effects. When pieces of charcoal, about an inch long, and one-sixth of an inch in diameter, were brought within l-30th or l-40th of an inch of each other, a bright spark was produced, and more than half the volume of the charcoal be- came ignited to whiteness; and by drawing back the points a little from each other, a constant discharge took place, through the heated air, in a space equal at least to four inches, producing a most brilliant ascend- ing arch of light, expanded and conical in the middle. When any substance was in-