125 



FLUORINE. 



FLUTE. 



120 



metals. The following are the chief remaining compounds of this 

 element : 



Hydrofluoric Acid (HF), a compound of fluorine and hydrogen, 

 which was first made known by Scheele. Mr. Knight (' Phil. Mag.,' 

 xvii., p 357) first suggested an apparatus for procuring it in a state of 

 purity, though not of the greatest strength. The properties of this 

 acid were minutely examined by Gay-Lussac and Thenard in 1810. 

 (' Recherches Physico-Chimiques.') Fluor-spar, or what is more cor- 

 rectly termed fluoride of calcium, is to be mixed with twice its weight 

 of strong sulphuric acid, and put into a leaden or silver retort, to which 

 a receiver of the same metal is to be adapted, and surrounded with ice 

 or snow mixed with salt. When a moderate heat is applied to the 

 retort the sulphuric acid acts upon the fluoride of calcium, in a mode 

 analogous.to that in which its action is exerted upon common salt in 

 preparing muriatic or hydrochloric acid ; the results are sulphate of 

 lime, which remains in the retort, while the fluorine of the fluoride 

 uniting with the hydrogen of the decomposed water of the sulphuric 

 acid forms hydrofluoric acid, which, coming over in the state of vapour, 

 is condensed in the cooled receiver; the product is best kept in a 

 silver bottle with a stopper of the same metal. 



The properties of this acid are, that it is fluid, clear, colourless, and 

 volatile ; and when it escapes into the air, it forms with the atmos- 

 pheric moisture white fumes, as hydrochloric acid does. Its vapour is 

 extremely pungent and irritating, and it acts strongly on vegetable 

 blues. The specific gravity of hydrofluoric acid is 1-0609, but by 

 the gradual addition of a certain quantity of water, the density may 

 be increased to 1-25. Its attraction for water is very great, and when 

 dropped into it they combine with a hissing noise. The liquid acid 

 is extremely corrosive ; when a drop is allowed to fall upon the skin 

 it produces painful sores. Until recently the concentrated acid here 

 described was supposed to be anhydrous, but it is now known to 

 contain water, which may be removed by the addition of anhydrous 

 phosphoric acid, the true anhydrous acid then escapes aa a colourless 

 gas of a very irritating odour and which by means of a freezing 

 mixture may be condensed to a colourless mobile liquid. 



The reason for the necessity of distilling and keeping this acid in 

 metallic vessels is that it acts upon and decomposes glass with great 

 facility, on account of its great affinity for silica which the latter 

 contains. Hence it has been rendered extensively useful for orna- 

 mental etching upon glass. 



When hydrofluoric acid U brought into contact with certain metals 

 it is decomposed, hydrogen gas being evolved, and a metallic fluoride 

 formed : upon potassium this action is extremely energetic, and is 

 attended with the evolution of gas and the formation of fluoride of 

 potassium. With metallic oxides it forms a fluoride and water. 



Hydrofluate of ammonia may be obtained by saturating the acid with 

 the alkali ; it is an unimportant salt, not being applied to any purpose 

 whatever. 



fluoride of Silicon, (SiF,) sometimes improperly termed Fluoti/icic 

 acid, is prepared by mixing equal quantities of fluoride of calcium and 

 silica with three times their weight of sulphuric acid in a retort ; on 

 the application of a moderate degree of heat action takes place ; and it 

 appears that the oxygen of the silica in transferred to the calcium of 

 the fluoride and convert* it into lime, which combining with the 

 niilphuric acid forms sulphate of lime, while the fluorine and silicon set 

 free combine to form fluoride of silicon, which rises in the gaseous 

 state, and is to be received in very dry air-jars filled with and inverted 

 in mercury. 



The gas thug obtained is colourless, its odour is peculiar, suffocating, 

 and acid, and it fumea on coming into contact with the moisture of 

 the air, but much less so than fluoboric acid gas. Its specific gravity, 

 according to Dr. Davy, is 3'600, while Dumas makes 3'574. It suffers 

 no change by exposure to a high temperature, and it has not been 

 liquefied by condensation. It is absorbed and decomposed by water, 

 forming a solution which contains a peculiar acid, the hydrojiuonlicic 

 ;u-irl i:;ilK, SiO ? ). 



When potassium is put into this gas, it inflames and burns. When 

 the gas is passed over iron heated to whiteness, there is formed an 

 extremely thin coating of fluoride of iron and silicium, and the gas 

 then passes without further alteration. 



It does not decompose the alkaline carbonates when dry at common 

 temperatures, nor is it absorbed by them, however long they may 

 remain in contact ; mint hydrated oxides however absorb it without 

 the assistance of heat. 



Fluoride of silicon condenses double its volume of ammoniac.il gas, 

 and forms with it a volatile compound, which is of no importance ; 

 when it acts uponmetallic oxides both are decomposed, the results 

 being silica and metallic fluorides. 



Fliivriilf -if /!', a, (BF 3 ) improperly termed flunboric acid, was 

 obtained by Uay-Lussac and Thenard by heating a mixture of fluor- 

 spar, or fluoride of calcium, and vitrified boracic acid. In this opera- 

 tion the oxygen of the. boracic acid combines with the calcium of 

 the fluoride of calcium and converts it into oxide of calcium or lime, 

 and the fluoiiue and boron then uniting form the compound in 

 question. The properties of this gaa are, that it is colourless, ban a 

 Nt odour, is deleterious to animal*, and extinguishes flame. It 

 rungly ; and when bubbles escape into the air, 

 li it* moisture and produce a very white dense fume. 



Water dissolves about 700 times its volume of this gas. The solu- 

 tion is strongly acid, and emits fumes, and is found to contain hydro- 

 fluoboric acid (HF, BF 3 ). This solution does not act upon glass, nor 

 does the gas itself ; but they readily decompose animal and vegetable 

 substances. Thus, a piece of paper put into the jar of the gas over 

 mercury is decomposed and charred as if burnt, by the abstraction of 

 the elements of water from it, for which the gas has so powerful an 

 affinity. When potassium is put into this gas it burns, and a brown 

 mixture of boron and fluoride of potassium is obtained. 



FLUOSILICIC ACID. [FLUORINE.] 



FLUTE, a well-known musical instrument, the use of which, under 

 different forms and names, may be traced to the remotest periods of 

 antiquity. Most of the ancient poets ascribe its invention to no less 

 personages than gods and goddesses. Even the grave Plutarch, in his 

 dialogue FUp! MOIOTI/CTJJ, attributes it to Apollo. Lucretius, however, 

 contents himself by deriving its origin from the breathing of western 

 winds over certain reeds, and thus, he tells us, was suggested to man 

 the rural pipe, a simple tube, which the ingenuity of later ages has 

 improved into one of the most elegant and fascinating instruments of 

 which art can boast. The word is said to be derived from the Latin 

 fluta, (lamprey), a kind of eel which has seven holes lengthways in its 

 side, and when extended resembles a very narrow flute. 



The ancient flute had some sort of mouth-piece ; it was double as 

 well as single that is, was often composed of two tubes, both played 

 together, and hence it has not unreasonably been inferred that the 

 enlightened nations of antiquity possessed some knowledge of harmony. 

 There is a figure of an ancient flute-player, or a terminal Pan, in the 

 Third Gneeo-Roman Saloon of the British Museum. The flute was 



almost universally employed by the Greeks, Romans. &c., not only in 

 their temples, theatres, social entertainments, and armies, but also in 

 their funeral ceremonies. It even may be said to have accompanied 

 their public orations, having frequently been employed for the purpose 

 of keeping the voice up to a proper pitch. From the custom of intro- 

 ducing it in the lost offices for the dead arose the saying, Jam licet 

 ad tibicines miltas (you may now send for the flute-players), when any 

 one was in articulo mortii in the last agonies. 



Of the old English flute for the invention whereof Mersenne 

 erroneously gives this country the credit we will say a few words. 

 It was not unfrequently called the flute a tee, from the resemblance 

 of the mouth-piece to the beak of a bird. This mouth-piece was at 

 the upper and wider end, and the instrument was held in the manner 

 of the oboe and clarionet. It had seven finger-holes, no keys, and was 

 commonly adapted either to the scale of C or F. The flute a bee 

 wag gradually superseded by that now in use, which long was known 

 as the German flute the flute traversicre, or horizontal. This, at first 



