Humphry Davy

REPORT OF CHEMISTRY, NATURAL PHILOSOPHY, &c. Tº: power by which bodies unite chemically, known by the name of affinity, and L the proportions in which they unite, called the atomic theory, have lately excited the chief attention of Chemists. It appears that Substances are deeomposed by electri city according to a determinate law. Oxygen and acids are attracted to the positive ole; while hydrogen, alkalies, earths, and metals, are attracted to the negative pole. is is considered as owing to an affinity subsisting between oxygen, and acids, and positive electricity; and between hydrogen, alkalies, earths and metals, and negative electricity. This discovery of Sir H. Davy pointed out the means of employing galva" nºsº decomposing many bodies which had previously resisted chemical experiment. He showed that bo. ilies which have a chemical affinity for each other are in different states of electricity. Thus, when buick-lime and oxalic acid are brought in contact, and separated, the acid is found te he negative, and the lime positive. Hence the reason why oxygen and acids are attracted by the negative pole of the battery. Hydrogen, alkalies, earths, and oxides, are in a positive state of excitement; therefore they are attracted to the nega tive pole of the battery. According to this doctrine, chemical affinity is the same power with the attraction which exists between bodies in different states of electrical excite ment.—In consequence of it, Sir H. Davy was led to attempt the decomposition of the alkalies and earths, and to obtain the splendid success with which these attempts were attended. BERzelius has bestowed much attention on this subject. According to him the acid or alkaline rature of a body depends upon the state of its electricity. If it be permanently negatire, it is of an acid mature; if it be permanently positire, it is alkaline, and a body may be positive with respect to one body, and negative with respect to another. The same great Chemist has given a table of the chemical snbstances in the order of the intensity of their electricities beginning with that which is attracted most strongly to the positive pole, or most intensely negatire; and terminating with the body which is attracted most strongly to the negative pole, and therefore nost intensely positire. The negative intensity diminishes as we proceed downwards in the table, and at last in the centre finally disappears, then the positive intensity begins and gradually increases, becoming greatest at the lower end of the table. Hence the affinity of the two sub stances at the two extremes of the table is greatest of all; and as we advance to the middle of the table, that affinity gradually diminishes, and at last disappears. Thus oxygen and potassium have the greatest affinity for each other; and there is very little affinity between iridium, platinum, and gold. Oxygen, Tungsten, Rhodinm, Manganese, &ulphur, Antimony, Palladium, Cerium, Nitricum. Tellurium, Mercury, Yttrium, Muriatic radicle, Silicon, Silver, Glucinum, Phosphorus, Columbium, Lead, Aluminium, Fluoric radicle, Titanium, Tin, Magnesium, Boron, Zirconium, Nickel,” Calcium, - Carbon, Osmium, Copper, Strontium, Hydrogen, Bismuth, Cobalt, Barytium, Arsenic, Iridium, Uranium, Sodium, Chromium, Platinum, Zinc, Potassium. Molybdenum, Gold, Iron » OERsted has adopted the electrical theory of affinity. He considers the phe momena of electricity, galvanism, magnetism, heat, light, and chemical affinity, as depending on the same forces; and the same cause, which in one case produces electri cal action, occasions in another chemical action. These actions are produced by two forces; the one negatire, the other positºre. These forces are opposite to one another; and by being made to act against one another, may suspend or destroy one another IHeat, says he, is produced by the extinction of the two forces, either in electrical or chemical processes. Light is derived from the same cause. Acids which are attracted to the same pole as oxygen, possess the same force with that principle; while alkalies and combustible bodies, which are attracted to the opposite pole, possess the opposite force. He arranges chemical substances under two series: the first containing the pro ducts of combustion; the second, the supporters and combustibles. Those of the one series, according to him, do not combine with those of the other; except sulphur and phosphorus, which combine both with the metals and alkalies, and therefore constitute, as it were, the transition from the one series to the other. Combustibility, then, is the prepouderance of the positive force in a particular state, called the state ºf suppºrters, or of the first class of bodies. Alkalinity presents the same force, but in a different state, called the state of products, or of the second class. - There exists three principal combinations between the electrical forces, which are the same as the chemical forces. Erpansion, which is the effect of a repulsive force in bo dies, is most frequently owing to an excess of one of the electric forces. Contractiºn is the effect of an equilibrium between the forces, and of their mutual extinction. The forces which produce the electrical and chemical actions of bodies are the same as those which produce the mechanical properties. Impenetrability depends on the resistance which the expansive power of two forces opposes to a body, endeavouring to penetrate the space already occupied by another body. Cohesion is the effect of the two force. which attract one another. Universal attraction consists in the action at a distance ºf the two forces upon each other, supposing the expansive power of each force not to ex tend beyond the surface of bodies. At preseut, concludes Dr. TwoMesos,

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