The elements of experimental chemistry (Volume 2).

  • Henry, William, 1774-1836.
Date:
1819
Catalogue details

Licence: Public Domain Mark

Credit: The elements of experimental chemistry (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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    U( CHAPTER XVII. FLUORIC ACID.. I. THE fluoric acid may be obtained from a substance found abun- <kntly in Derbyshire, under the name of fluor spar. In converting this spar to ornamental purposes, small pieces are broken off, which may be had at a cheap rate. Pure fluoric acid has never yet been obtained in a gaseous state; for vve are acquainted with it, as a gas, in only two forms, viz. lstly, of combination with silex; and 2dly, with boracic acid. Sijicated fluoric gas may be prepared by pouring on fluor spar, finely powdered, and mixed with half its weight of powdered glass, an equal weight of strong sulphuric acid. It may be received over mercury in glass vessels, the transparency of which it does not impair. Its specific gravity is very great, 100 cubic inches weighing 110.78 grains. By causing a known volume of it to be absorbed by liquid ammo- nia, Dr. John Davy separated the silex, which formed 61.4 per cent, of the weight of the gas. When the gas is absorbed by water, much of the silex is deposited, and it retains only 54.5 per cent, of that earth in combination. To this liquid, Dr. Davy gives the name of siibsilicated fluoric acid. Water absorbs about 263 times its bulk of the gas, and the solution may be kept in glass vessels without corroding them. It condenses twice its volume, and no other proportion, of ammo- niacal gas, forming a dry white salt, which is slightly acid; deposits some silex when dissolved in water; and, when its concentrated solu- tion is boiled in glass vessels, powerfully corrodes them. When an excess of liquid ammonia is added, the whole of the silex is precipi- tated, and a pure filiate of ammonia is obtained. Potassium, heated in silicated fluoric gas, takes fire, and burns with a deep red light. In an experiment of Sir H. Davy, after the com- bustion, the whole of the fluoric acid was found to be destroyed, and no gas left but a residuum of hydrogen. But from fluoric acid, long exposed to calcined sulphate of soda, hardly one-tenth its bulk of hy- drogen could be thus developed. The bottom of the retort, in these cases, was covered with a sub- stance of various colours, in some parts chocolate, in others yellow, which, being heated in contact with air, burned slowly, lost its colour, and became a white saline mass. In oxygen gas, it burned with an absorption of oxygen, but not with any great intensity, reproducing silicated fluoric acid gas. By the action of this substance on water, fluoric acid and potash were generated; and some chocolate-coloured particles were sepa- rated by the filter, which, when dried, and heated in oxygen gas,