Fluorine

“ When it is desired to determine the action of fluorine upon a solid substance, the following method of procedure is adopted. A preliminary experiment is first made, in order to obtain some idea as to the degree of energy of the reaction, by bringing a little of the solid, placed upon the lid of a platinum crucible held in a pair of tongs, near the mouth of the delivery tube of the preparation apparatus. ”

“ The best mode of obtaining the fluoride of platinum for this purpose is to heat a bundle of platinum wires to low redness in the fluorspar reaction tube in a rapid stream of fluorine. As soon as sufficient fluoride is formed on the wires, they are transferred to a well stoppered dry glass tube, until required for the preparation of fluorine. ”

“ It is the only mineral at all common from which fluorine can be obtained, and is used for making hydrofluoric acid, and other chemical compounds of this element. It is, however, of much greater importance as a flux in reducing iron, silver, lead and copper ores. In the industries it finds a place, being used to make apochromatic lenses, cheap jewelry, and for the electrodes in flaming arc lamps. ”

“ According to Moissan, fluorine is disengaged by the action of an electric current on fused hydrogen potassium fluoride, KHF2. The present state of chemical knowledge is such that the knowledge of the properties of an element is much more general than the knowledge of the free element itself. It is useful and satisfactory to learn that even fluorine in the free state has not succeeded in eluding experiment and research, that the efforts to isolate it have been crowned with success, but the sum total of chemical data concerning fluorine as an element gains but little by this achievement. ”

“ Failing to eat as large proportions of bran as our ancestors did, we are deprived to a large degree of the fluorine which they contain. The enamel of the teeth has more fluorine, in the form of fluoride of calcium, than any other part of the body. Fluorine might, indeed, be regarded as the characteristic chemical constituent of this structure, the hardest of all animal tissue; hence a supply of fluorine, while the development of the teeth is proceeding, is essential to the proper formation of the enamel, and any deficiency in this respect must result in thin and inferior enamel. ”

“ The methods of its preparation show that it does not combine with oxygen, although Troost and Ouvrard state that it unites with magnesium vapour. It forms no compounds with hydrogen, chlorine, phosphorus, sulphur, sodium, tellurium, etc. Even fluorine, probably the most generally active of the chemical elements, shows no tendency to unite with it. ”

“ Although the existence of the element fluorine was surmised as far back as 1771, when Scheele first recognised that the product of the action of oil of vitriol upon fluor-spar contained a hitherto unknown substance, it was not until 1886 that this substance was definitely isolated by Moissan by the electrolysis of the acid potassium fluoride in solution in hydrogen fluoride. Cerium tetrafluoride, CeF4, and lead tetrafluoride, PbF4, when heated, were observed by Brauner to evolve a gas having a smell resembling that of hypochlorous acid, which was probably free fluorine. ”

“ By the application of cold and pressure it may be liquefied. At still lower temperatures34 it may be frozen to a white solid. Fluorine is characterised by an extraordinary chemical activity, and combines, even at ordinary temperatures, with a large number of substances. Sulphur, phosphorus, arsenic, antimony, boron, iodine, and silicon inflame or become incandescent in contact with it. It combines with hydrogen with explosive violence, even in the dark and at the lowest temperature. It unites also with the metals, occasionally with incandescence, and decomposes water with liberation of oxygen. ”

“ Indeed, owing to the powerful affinity of mercury for fluorine, it is a most dangerous experiment to transfer a tube containing fluorine gas, filled according to either the first or second method, to the mercury trough; the tube is always shattered if the mercury comes in contact with the gas, and generally with a loud detonation. Fluorine may, however, be preserved for some time in tubes over mercury, provided a few drops of the non-reacting liquid are kept above the mercury meniscus. ”

“ Silicon dioxide, one of the most inert of substances at the ordinary temperature, takes fire in the cold in contact with fluorine, becoming instantly white-hot, and rapidly disappearing in the form of silicon tetrafluoride. The chlorides of both boron and silicon are decomposed by fluorine, with formation of fluorides and liberation of chlorine, the reaction being accompanied by the production of flame. ”

“ As a liquid at −210° fluorine attacks turpentine also cooled to that temperature with explosive force and the evolution of light, while the direction of a jet of hydrogen upon its surface is immediately followed by combination and a flash of flame. Even when the point of a tube containing solid fluorine is broken off under liquid hydrogen, a violent explosion ensues. ”

“ I have been hard at work. I have expelled fluorine from fluate of lead, fluate of silver, and fluate of soda by chlorine. It is a new acidifier, forming three powerful acids; hydrofluoric, silicated fluoric, and fluo-boric. It has the most intense energies of combination of any known body, instantly combining with all metals, and decomposing glass. Like the fabled waters of the Styx, it cannot be preserved, not even in the ape’s hoof. We have now a triad of supporters of combustion.”
The results of Davy’s work were communicated to the Royal Society on July 8th, 1813. ”

“ But, as we have seen and already know, hydrogen enters into direct combination with very few substances, and then only under special circumstances; whilst oxygen, as we shall soon learn, combines with nearly all substances. Only gaseous chlorine (and, especially, fluorine) is capable of decomposing water, taking up the hydrogen from it, without combining with the oxygen. ”

“ The stability of endothermic bodies like nitric oxide and ozone at low temperatures requires further investigation. The behaviour of fluorine, which may be regarded as the most active of the elements, is instructive in this respect. As a gas, cooled to −180° C. it loses the power of attacking glass; similarly silicon, borax, carbon, sulphur and phosphorus at the same temperature do not become incandescent in an atmosphere of the gas. Passed into liquid oxygen, the gas dissolves and imparts a yellowish tint to the liquid ”

“ Organic compounds are rapidly attacked by the gas.
Only one compound of hydrogen and fluorine is known, namely hydrofluoric acid, HF or H2F2, which was first obtained by C. Scheele in 1771 by decomposing fluor-spar with concentrated sulphuric acid, a method still used for the commercial preparation of the aqueous solution of the acid, the mixture being distilled from leaden retorts and the acid stored in leaden or gutta-percha bottles. ”

“ The proper evidence of the reality of any supposed new analysis is, that it is more consistent with the known analogies of chemistry, to suppose the process analytical than synthetical. Thus, as has already been said, chemists admit the existence of fluorine, from the analogy of chlorine; and Davy, when it was found 310 that ammonia formed an amalgam with mercury, was tempted to assign to it a metallic basis. ”

“ To standardise the solution, weigh up 0.25 gram of pure iodine in a small beaker. Add 2 or 3 crystals of potassium iodide; cover with water; and, when dissolved, dilute to 50 or 100 c.c. Titrate, and calculate the standard.
FLUORINE AND FLUORIDES.
Fluorine is frequently met with as calcium fluoride or fluor-spar (CaF2) . It occurs less abundantly as cryolite (Na3AlF6) , a fluoride of aluminium and sodium, which is used in glass-making. Certain other rarer fluorides are occasionally met with. ”

“ The truth of this forecast has been established of recent years by Henri Moissan, who isolated gaseous fluorine by subjecting a mixture of hydrofluoric39 acid and hydrogen potassium fluoride contained in a platinum U tube to the action of a powerful electric current. ”

“ Inasmuch as the experiments described are of so extraordinary a nature, owing to the intense chemical activity of fluorine, and are so important as filling a long existing vacancy in our chemical literature, readers of Nature will doubtless be interested in a brief account of them. ”

“ Fused potash yields potassium fluoride and ozone. Aqueous potash does not form potassium hypofluorite when fluorine is bubbled into it, but only potassium fluoride. Lime becomes most brilliantly incandescent, owing partly to the excess being raised to a very high temperature by the heat developed during the decomposition, and partly to the phosphorescence of the calcium fluoride formed.
Sulphides of the alkalies and alkaline earths are also immediately rendered incandescent, fluorides of the metal and sulphur being respectively formed. ”

“ Fluorine.—F, Cl, Br, I, are called halogens or haloids, and exist in compounds—salts—in sea water. F is the most active of all elements, combining with every element except O. Until recently it has never been isolated, for as soon as set free from one compound it attacks the nearest substance, and seems to be as much averse to combining with itself, or to existing in the elementary state, as to uniting with O. It is supposed to be a gas, and, as is claimed, has lately been isolated by electrolysis from HF in a Pt U-tube. ”

“ In experimenting upon liquids, great care is necessary, as the reaction frequently occurs with explosive violence. A preliminary experiment is therefore always made, by allowing the fluorine delivery tube to dip just beneath the surface of the liquid contained in a small glass cylinder. ”

“ If a gaseous or liquid product results, and it is desirable to collect it for examination, small fragments of the solid are placed in a platinum tube connected to the delivery tube by flexible platinum tubing or by a screw joint, and the resulting gas may be collected over water or mercury, or the liquid condensed in a cooled cylinder of platinum. In this manner the action of fluorine upon sulphur and iodine has been studied. ”

“ Tantalum pentafluoride, TaFl5, for a long time only known in solution, may be obtained by passing fluorine over an alloy of tantalum and aluminium, and purifying by distillation in a vacuum. It forms colourless, very hygroscopic prisms, which attack glass, slowly at ordinary temperatures, more rapidly when heated (Ber., 1909, 42, p. 492) . Its double salts with the alkaline fluorides are very important, and serve for the separation of the metal from columbium and titanium. ”

“ In the spring of 1813 he was engaged on the chemistry of fluorine, and though he failed to isolate the element, he reached accurate conclusions regarding its nature and properties. In October he started with his wife for a continental tour, and with them, as “assistant in experiments and writing,” went Michael Faraday, who in the previous March had been engaged as assistant in the Royal Institution laboratory. ”

“ Iron, reduced by hydrogen, combines in the cold with immediate incandescence, and formation of an anhydrous, readily soluble, white fluoride. Aluminum, on heating to low redness, gives a very beautiful luminosity, as do also chromium and manganese. The combustion of slightly warmed zinc in fluorine is particularly pretty as an experiment, the flame being of a most dazzling whiteness. Antimony takes fire at the ordinary temperature, and forms a solid white fluoride. Lead and mercury are attacked in the cold, as previously described, the latter with great rapidity. ”

“ The former are by far the more numerous, altogether numbering more than fifty. Among the better known are such well known substances as iron, mercury, copper, tin, potassium, antimony, strontium, and nickel. The non-metals are more widely distributed and together made up of the bulk of the universe.
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They comprise the gases—oxygen, hydrogen, nitrogen, and chlorine, and such substances as sulphur, carbon, phosphorus and iodine. To the latter class also belongs a peculiar element called fluorine, which, when combined with hydrogen, destroys glass. ”

“ In his paper of 1887, the main outlines of which were given in Nature at the time (1887, vol. xxxvii., p. 179) , M. Moissan showed that pure hydrofluoric acid readily dissolves the double fluoride of potassium and hydrogen, and that the liquid thus obtained is a good conductor of electricity, rendering electrolysis possible. It will be remembered that, by passing a strong current of electricity through this liquid contained in a platinum apparatus, free gaseous fluorine was obtained at the positive pole and hydrogen at the negative pole. ”

“ Bromine 309 was only discovered as late as 1826; and Fluorine, or Phtore, as, from its destructive nature, it has been proposed to term it, has not been obtained as a separate substance, and is inferred to exist by analogy only. The analogies of these bodies (Chlore, Phtore, &c.) are very peculiar; for instance, by combination with metals they form salts; by combination with hydrogen they form very strong acids; and all, at the common temperature of the atmosphere, operate on other bodies in the most energetic manner. ”

“ Because of its great activity it is extremely poisonous. Fluorine does not form any oxides, neither does it form any oxygen acids, in which respects it differs from the other members of the family.
Hydrofluoric acid (HF) . Hydrofluoric acid is readily obtained from fluorspar by the action of concentrated sulphuric acid. The equation is
CaF2 + H2SO4 = CaSO4 + 2HF.
In its physical properties it resembles the binary acids of the other elements of this family, being, however, more easily condensed to a liquid. ”