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 1).

  • Andrew Ure
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 1). 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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    but when potassium is strongly heated in it, it takes fire and burns with a deep red light; the gas is absorbed, and a fawn-co- loured substance is formed, which yields alkali to water with slight effervescence, and contains a combustible body. The washings afford potash and a salt, from which the strong acid fluid previously de- scribed, may be separated by sulphuric acid. The gas formed by the action of liquid sulphuric acid on a mixture containing silica and fluor spar, the silicated fluoric gas or fluo-silicic acid, may be regarded as a compound of fluoric acid and silica. It affords, when decomposed by solution of ammonia, 61.4 per cent of silica; and hence was at first supposed by Sir H. Da- vy to consist of two prime proportions of acid = 2.652 and one of silica = 4.066, the sum of which numbers may represent its equivalent = 6.718. One volume of it con- denses two volumes of ammonia, and they form together a peculiar saline substance which is decomposed by water. The com- position of this salt is easily reconciled to the numbers given as representing silica and fluoric acid, on the supposition that it contains 1 prime of ammonia to 1 of the fluosilicic gas; for 200 cubic inches of am- monia weigh 36.2 gr. and 100 of the acid gas 110.77. Now 36.2 : 2.13 : : 110.77 : 6.52. Dr. John Davy ob'ained, by exposing this gas to the action of water,^'^ of its weight of silica; and from the action of water of ammonia he separated JL\i of its 1 10 0 0 weight. Hence 100 cubic inches consist by weight of 68 silica and 42 of unknown fluoric matter, the gas which holds the silica in solution. Sir H. Davy, however, conceives that this gas is a compound of the basis of silica, or silicon, with fluorine, the supposed basis of fluoric acid. If, instead of glass or silica, the fluor spar be mixed with dry vitreous boracic acid, and distilled in a glass vessel with sulphu- ric acid, the proportions being one part boracic acid, two fluor spar, and twelve oil of vitriol, the gaseous substance formed is of a different kind, and is called thefluo- boric gas. 100 cubic inches of it weigh 73.5 gr. according to Sir II. Davy, which makes its density to that of air as 2.41 is to 1.00; but M. Thenard, from Dr. John Davy, states its density to that of air as 2.371 to 1.000. It is colourless; its smell as pungent, and resembles that of muriatic acid; it cannot be breathed without suf- focation ; it extinguishes combustion; and reddens strong]}' the tincture of turnsole. It has no manner of action on glass; but a very powerful one on vegetable and ani- mal matter: It attacks them with as much force as concentrated sulphuric acid, and appears to operate on these bodies bv Vol. i. [ 6 ] the production of water; for while it car- bonizes them, or evolves carbon, they may be touched without any risk of burning. Exposed to a high temperature, it is not decomposed; it is condensed by cold without changing its form. When it is put in contact with oxygen, or air, either at a high or low temperature, it experiences no change, except seizing, at ordinary temperatures, the moisture which these gases contain. It becomes in consequence a liquid which emits extremely dense va- pours It operates in the same way with all the gases which contain hygrometric ^ater. However little they may contain, it occasions in them very perceptible va- pours. It may hence be employed with ad- vantage to show whether or not a gas con- tains moisture. No combustible body, simple or com- pound, attacks fluoboric gas, if we except the alkaline metals. Potassium and sodi- um with the aid of heat, burn in this gas, almost as brilliantly as in oxygen. Boron and fluate of potash, are the products of this decomposition. It might hence be in- ferred that the metal seizes the oxygen of the boracic acid, sets the boron at liberty, and is itself oxidized and combined with the fluoric acid. According to Sir II. Da- vy's views, the fluoboric gas being a com- pound of fluorine and boron, the potassium unites to the former, giving rise to the fluoride of potassium, while the boron re- mains disengaged. Fluoboric gas is very soluble in water. Dr. John Davy sa}s, water can combine with 700 times its own volume, or twice its weight at the ordinary temperature and pressure of the air. The liquid has a spe- cific gravit\ of 1.770. If a bottle contain- ing this gas be uncorked under water, the liquid will rush in and fill it with explosive violence. Water saturated with this gas is limpid, fuming and very caustic. By heat, about one-fifth of the absorbed gas may be expelled; but it is impossible to abstract more. It then resembles concentrated sul- phuric acid, and boils at a temperature considerably above 212°. It afterwards condenses altogether, in stria:, although it contains still a very large quantity of gas. It unites with the bases, forming salts, call- ed fluoborates. none of which has been applied to any use. The most important will be described under their respective bases. The 2d part of the Phil. Transactions for 1812, contains an excellent paper by Dr. John Davy on fluosilicic and fluoboric gases, and the combinations of the latter with ammoniacal gas. When united in equal volumes, a pulverulent salt is form- ed; a second volume of ammonia, howev- er, gives a liquid compound; and a third of ammonia, which is the limit of combi-