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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    MM. Gay-Lussac and Thenard announc- ed, that the power of chemical decomposi- tion increases only as the cube root of the number of plates; but their experiments were made with parts of piles, says Sir H. Davy, very unfavourable for gaining ac- curate results. In various trials made by him, with great care, in the laboratory of the Royai Institution, the results were al- together different. The batteries employed were parts of the above great combination, carefully in- sulated, and similarly charged; arcs of zinc and silver presenting equal surfaces, ar- ranged in equal glasses, filled with the same kind of fluid, were likewise used; and the tubes were precisely similar, and filled with the same solution of potash. In these experiments, 10 pairs of plates produced 15 measures of gas; 20 pairs pro- duced in the same time 49; again, 10 pairs produced five measures; 40 pairs in the same time produced 78 measures. In ex- periments made with arcs, and which seemed unexceptionable, 4 pairs produced 1 measure of gas. 12 in the same time 9-^g- When 6 produced 1 30 - - 24.5 Now, these quantities are nearly as the squares of the number of pairs. In batteries, whose plates have equal areas, the calorific power has been said to be as the number. Sir H. Davy, however, found that when the surface of each was 100 square inches, 10 pairs ignited 2 inches of plat, wire l-80th of an inch. 20 do. do. 5 inches do. do. 40 do. do. 11 inches do. do. The results of experiments on higher numbers were not satisfactory; for 100 pairs, of 32 square inches each, ignited three inches of platinum wire l-70th of an inch; and 1000 ignited only 13 inches. The charges of exciting acid, were similar in both cases. The ratio between the increase of calo- rific power, and increased area of the plates, is probably greater than even the square. For 20 pairs of plates, containing each two square feet, did not ignite one-sixteenth as much wire, as 20 pairs, containing each eight square feet; the acid employed being of the same strength in both cases. But great difficulties occur to ensure accuracy, in experiments on extensive and powerful batteries. In Sir EJ. Davy's great Bakerian Lecture on the chemical agencies of electricity, published in the Phil. Trans, for 1807, and most deservedly crowned by the National Institute of France with the Napoleon prize, he amply demonstrated that acids, which are electrically negative, with respect to alkalis, metals, and earths, are separated from these bodies in the voltaic circuit at the positive pole; and alkalis, metals, and earths, are separated from acids, :.t the negative surface. He showed further, that such are the attracting powers of these sur- faces, that acids are transferred through alkaline solutions, and alkalis through acid solutions, to the poles where they have their points of repose. This was exhibited by making a combination of three agate cups, one containing sulphate of potash, one weak nitric acid, and the third disnlled water. The three >vere connected by as- bes*us moistened in pure water, in such a manner, that the surface of the acid was lower than the surface of the fluid, in the other two cups. When two wires of pla- tina from a powerful voltaic apparatus, are introduced into the two extreme cups, the solution of the salt being positively elec- trified, a decomposition took place, and in a certain time, a portion of potash was found dissolved in the cup, in contact with the negative wire, though the fluid in the middle cup was still sensibly acid. Such are the chemico-analytical powers of electricity, that not even insoluble com- pounds are capable of resisting their ener- gy; for even glass, sulphate of barytes, fluor spar, g\psum, marble, &c. when moistened and placed in contact with electrified sur- faces, from the voltaic apparatus, are sen- sibly acted on, and the alkaline, earthy, or acid matter, slowly carried to the poles in the common order. Not even the most solid aggregates, nor the firmest com- pounds, are capable of resisting this mode of attack. Its operation is slow, but the results are certain, and, sooner or later, by means of it, bodies are resolved into simpler forms of matter. Till Sir H. Davy established the grand law of electro-chemical decomposition, that metals, inflammable bodies, alkalis, earths, and oxides, are determined to the negative surface or pole, and oxygen, chlorine, io- t dine, and acids, to the positive pole, it had been imagined that various substances might be generated from pure Water, by means of electricity, such as potash, soda, and muriatic acid. A strict investigation of the circumstances under which these substances appeared, led him to discover that they were always furnished from the vessels, or from impurities in the water, and enabled him to determine the general principles of electrical decomposition, and to apply this power to the resolution of se- veral species of -natter of unknown nature into their elements, namely the alkalis, earths, boracic and muriatic acids, &c. The intimate relation between the elec- trical and chemical changes, is evident likewise in the general phenomena of the battery. The most powerful voltaic com-