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FLUORIC ACID FLUSHING. 



This gas has received the name of fluo-silicic acid, 

 because it is regarded as a compound of fluoric acid 

 und silica. A better mode of procuring it, however, 

 is to mix fluor-spar with pounded glass, and, intro- 

 ducing the mixture into a glass retort, to add 

 sulphuric acid, and apply a moderate heat : the gas 

 will make its appearance in abundance, and may be 

 received in glass jars over the mercurial bath. It is 

 about forty-eight times denser than hydrogen. When 

 brought into contact with water, it is instantly absorb- 

 ed, depositing its silica in a white, gelatinous mass, 

 which is a hydrate of silica. It produces white 

 fumes when suffered to pass into the atmosphere. 

 From the strong affinity of fluoric acid for silica, it 

 cannot be preserved in glass bottles ; and is there- 

 fore kept in vessels of lead or silver. For the same 

 reason, fluoric acid is employed for etching on glass 

 its only important application. The glass is 

 covered with a thin coat of wax, or is brushed over 

 with a solution of isinglass in water ; and, when 

 this is dried, lines are easily traced by a graver. 

 It is then exposed to the action of the acid in the 

 state of gas ; the parts of the glass thus exposed are 

 soon eroded, the impression being more or less deep, 

 according to the time during which it is exposed. 

 Such a method, were it possible to obviate com- 

 pletely the defect from the brittleness of glass, has, 

 from the hardness of that substance, the important 

 advantage over copper, that the impressions do not 

 become less delicate from the fineness of the lines 

 being diminished by the pressure in throwing them 

 off. Different methods have been proposed to ren- 

 der the method practicable ; and engravings, though 

 not of much delicacy, have even been taken. As all 

 other acids are compound, Gay-Lussac and Thenard 

 conceived the fluoric acid as such also, and adopted 

 the opinion that it is composed of a certain combust- 

 ible body and oxygen gas. They accordingly at- 

 tempted to decompose it by means of some substance 

 which has a strong affinity for oxygen, and em- 

 ployed potassium for that purpose. When that 

 metal is brought into contact with fluoric acid, a 

 violent action ensues, accompanied with an explosion, 

 unless the experiment is cautiously conducted. Hy- 

 drogen gas is disengaged, and a white solid is pro- 

 duced, which has all the properties of fluate of 

 potash ; the explanation of which, given upon this 

 view, was, that the hydrogen arises from the de- 

 composition of water, that the oxygen of that fluid 

 combines with the potassium, and that the potash so 

 formed unites with the fluoric acid. They infer, 

 therefore, from their experiments, that the strongest 

 fluoric acid hitherto prepared contains water. 



On the other hand, Sir H. Davy contended that 

 fluoric acid, in its strongest form, is anhydrous ; for, 

 on combining it with ammoniacal gas, a dry fluate 

 of ammonia is formed, from which no water can be 

 expelled by heat. He maintained, also, that fluoric 

 acid is composed, not of an inflammable base and 

 oxygen, but of hydrogen united with a negative 

 electric body, analogous to chlorine, to which he has 

 given the name of fluorine. According to this view, 

 when the metal potassium is brought into contact 

 with fluoric acid, the hydrogen is not derived from 

 water, but from the acid, and the supposed fluate of 

 potash is a compound of fluorine and potassium. 

 The phenomena are explained with the same ease 

 by either theory, although the arguments upon 

 *hich they depend are thought, by the majority of 

 chemists, to preponderate in favour of the view pro- 

 posed by Sir Humphrey Davy. 



Fluoric acid forms salts by uniting with several 

 bases. Five fluates have hitherto been found native ; 

 viz., the fluate of lime, or fluor-spar, the fluo-silicate 

 of alumine, or topaz, the fluate of cerium, the double 



fluate of cerium and yttria, and the double fluate of 

 soda and alumine, or cryolite. The four latter are 

 very rare minerals, but the first is abundant. Potash 

 unites witli fluoric acid in two proportions, forming 

 a fluate and a bifluate, the former of which consists 

 of one atom and the latter of two atoms of acid 

 united with one atom of the alkali. A neutral fluate 

 of soda may be obtained directly from fluoric acid 

 and carbonate of soda. It melts with more difficulty 

 than glass ; 100 parts of water, at 212 Fahrenheit, 

 dissolve only 4.3 of it. Neutral fluate of ammonia 

 is more volatile than sal-ammoniac. It is easily ob- 

 tained by heating one part of dry sal-ammoniac, 

 with a little more than two parts of fluate of soda, 

 in a crucible of platinum, with its lid turned up- 

 wards. The earthy fluates are best formed by 

 digesting their recently precipitated moist carbonates 

 in an excess of fluoric acid. That of barytes is 

 slightly soluble in water, and readily in muriatic 

 acid. The neutral fluates of fixed bases are fusible 

 at a high temperature, and are not decomposed by 

 heat and combustible matter; nor does any acid, 

 excepting the boracic, effect their decomposition, 

 provided they are free from moisture. When 

 digested, on the contrary, in concentrated sulphuric, 

 phosphoric or arsenic acids, the fluoric acid is dis- 

 engaged, and may be recognised by its property of 

 corroding glass. If, instead of glass, the fluor-spar 

 be mixed with dry vitreous boracic acid, and distilled 

 in a glass vessel with sulphuric acid, the proportions 

 being 1 part boracic acid, 2 fluor-spar, and 12 sul- 

 phuric acid, the gaseous substance formed is of a 

 different kind, and is called fluo-boric acid. Its 

 density to that of air is as 2.371 to 1.000. It is 

 colourless. Its smell is pungent. It cannot be 

 breathed without suffocation. It extinguishes com- 

 bustion, and reddens vegetable blues. It has no ac- 

 tion on glass, but a very powerful one on vegetable 

 and animal matter, converting them into a carbona- 

 ceous substance. It has a singularly great affinity 

 for water. When it is mixed with air, or any gas 

 which contains watery vapour, a dense white cloud 

 appears, which is a combination of water and fluo- 

 boric acid gas. From this circumstance, it forms an 

 exceedingly delicate test of the presence of moisture 

 in gases. Fluo-boric acid gas is rapidly absorbed 

 by water. When potassium is heated in fluo-boric 

 acid gas, it inflames, and a chocolate-coloured solid, 

 wholly devoid of metallic lustre, is the sole product. 

 On putting this substance into water, a part of 

 it dissolves, and a solution of fluate of potash is 

 obtained, the insoluble matter being boron. Ac- 

 cordingly, fluo-boric acid gas is inferred to be a 

 compound of fluoric and boracic acids. It unites 

 with ammoniacal gas in three proportions, forming 

 salts, one of which is solid, and the two others 

 liquid. Other compounds of this acid, with salifi- 

 able bases, are scarcely known. 



FLUSHING (Fliessingen), a well fortified city on 

 the south side of the island of Walcheren, belonging 

 to the province of Zeeland, in the kingdom of the 

 Netherlands, lies at the mouth of the Western 

 Scheldt, and is connected with Middleburg, by a 

 caiial. Population, 4600. Flushing is the seat of 

 an admiralty office, and of the marine department 

 of the 'Scheldt. The greatest curiosity is the new 

 harbour, which is capable of containing eighty men- 

 of-war. It is on the eastern side of the city, with 

 two jetties projecting far into the sea. A comman- 

 dant of the third class resides here. There is also a 

 scientific academy here. It is the native place of 

 admiral De Ruyter (q. v.), and the spot where the 

 first standard of revolt from Spain was raised. 1 1 

 has a brisk commerce with the East Indies. Lat 

 51 20' 42" N.: Ion. 3 34' 57" E. 



