Fluoride

“ The fluoride is insoluble in water and mineral acids, as well as in excess of precipitant; this behaviour allows of a complete and easy separation of thorium from titanium and zirconium. The rare earth fluorides are also much more easily soluble in concentrated mineral acids than thorium fluoride, so that this compound may also be used in the separation from the rare earths. When heated in a stream of the acid to 800°, the hydrated salt yields the oxyfluoride, ThOF2; ignited in the air, it leaves the dioxide. ”

“ 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. ”

“ If the quantity of water is greater, the solution may be preserved for some minutes without decomposition. If the liquid is boiled, it decomposes instantly. At a red heat platinic fluoride decomposes into metallic platinum and fluorine, which is evolved in the free state. This reaction can therefore be employed as a ready means of preparing fluorine, the fluoride only requiring to be heated rapidly to redness in a platinum tube closed at one end, when crystallized silicon held at the open end will be found to immediately take fire in the escaping fluorine. ”

“ Hydrofluoric acid is used for etching glass and opening up silicates. It attacks silica, forming fluoride of silicon (SiF4) , which is volatile. Silica is by this means eliminated from other oxides, which, in the presence of sulphuric acid, are fixed. The commercial acid is seldom pure, and generally weak; and the acid itself is dangerously obnoxious. The use of ammonium fluoride (or sodium fluoride) and a mineral acid is more convenient. Determinations of this kind are made in platinum dishes enclosed in lead or copper vessels in a well-ventilated place. ”

“ By heating a mixture of fluorspar and ground flints with sulphuric acid a gaseous tetra-fluoride of silicon is formed, which, being partially soluble in water, yields an acid solution of the tetra-fluoride. Caustic potash is then added to the acid solution of the tetra-chloride until it becomes neutralised, and the sparingly soluble silico-fluoride of potassium thus formed is thoroughly dried and mixed in a glass or iron tube with eight or nine tenths of its weight of potassium or half its weight of sodium, and heated. ”

“ 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. ”

“ 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. ”

“ Fluor, flōō′or, n. a mineral often described as chemically fluate of lime, but really calcium fluoride, found abundantly in Derbyshire—also Flu′or-spar, Flu′orite.—ns. Fluores′cein, a coal-tar product, little used in dyeing, the colour not being fast; Fluores′cence, a peculiar blue appearance exhibited by certain substances exposed to sunlight, and especially observable in a dilute solution of sulphate of quinine.—adjs. Fluores′cent, having the property of fluorescence; Fluor′ic.—ns. Flu′oride, a binary compound of fluorine with another element ”

“ Re-filter sample if necessary, then inject a sample aliquot into the ion chromatograph. Measure peak height.
CALCULATIONS: 15. 16.
Determine mass (μg) of fluoride found on the front (W f) and back (W b) sections, and in the average media blank front (B f) and back (B b) sorbent section. Calculate concentration C of sulfuryl fluoride (mg/m 3) in the actual air volume, V (L) , applying the conversion factor 2.686 (MW SO 2F2/MW F -; the reaction is SO 2F2 + 4NaOH → 2NaF + Na 2SO 4 + 2H 2O) :
EVALUATION OF METHOD: This method was evaluated over the range 20 to 420 mg/m 3. ”

“ Hydrofluoric acid and its derivatives both in their manufacture and use and in the superphosphate industry affect the health of the workers.
If hydrogen fluoride or its compounds escape into the atmosphere they attack the respiratory passages and set up inflammation of the eyes; further, workers handling the watery solutions are prone to skin affections (ulceration) . ”

“ 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. ”

“ It rarely fails to break perfectly true.
Etching on Glass.
Acid sulphuric, a sufficient quantity to decompose the ammonia fluoride and making the mixture of a semi-fluid consistency. It must be prepared in a leaden vessel. It can be used with a common pen, but must be kept in bottles coated inside with paraffine, beeswax, or gutta-percha, with rubber stoppers. ”

“ Place a 10 mL aliquot of fluoride standard solution into a 100 mL volumetric flask, dilute to the mark and mix thoroughly. The solution is stable for at least 4 weeks at room temperature. 9.
To prepare the impregnated filter, evenly distribute 120 μL 0.75 M Na2CO3 over the surface of the filter and allow to dry at room temperature for several hours.
See Special Precautions 1.
Sampler: 37-mm diameter cellulose nitrate pre-filter, 0.8 μm pore size, 37-mm impregnated cellulose nitrate filter. The untreated filter collects particulate fluorides, while the impregnated filter collects HF vapor. ”

“ In order to be used in steel-making, the fluorspar after being concentrated should contain at least 85 per cent calcium fluoride and less than 4 per cent silica. Chemical and enameling industries require material with 95 to 98 per cent calcium fluoride and less than 1 per cent silica.
The chief foreign producer of fluorspar is Great Britain, and much of this product comes to the United States. Canada [Pg 194] produces a small amount, some of which also comes to the United States. Several thousand tons are produced yearly in Germany and France, and are largely consumed there. ”

“ 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. ”

“ This acid in the pure state is not an electrolyte, but when potassium fluoride is dissolved in it, a current from ninety Bunsen elements decomposes it, evolving hydrogen from the negative and fluoride from the positive electrode.
The apparatus employed in this process is constructed of platinum, and is made in the form of a U tube, as shown in the accompanying illustration, with fluorspar stoppers, through which the battery terminals, made of platinum iridium alloy, are led. The gas is liberated at about the rate of two liters per hour, and has very powerful chemical properties. ”

“ Fluoride of calcium, 234 parts by weight; double fluoride of cryolite, 421 parts by weight; fluoride of aluminum, 845 parts by weight. To these add three to four per cent of a suitable chloride—for example, calcium chloride. To this add alumina sufficient to form a very stiff mixture. Before electrolysis can begin the above are fused by means of heat, which should not exceed 1,210° F. The heat is obtained from a furnace heated by gas, coke, or charcoal, care being taken that no gases from the furnace enter the crucible. ”

“ An amorphous insoluble compound, K2ThF6,4H2O, is obtained by boiling the hydroxide with a mixture of potassium hydrogen fluoride and hydrofluoric acid. Sodium and ammonium fluorides throw down the simple fluoride.
Thorium chloride, ThCl4, is obtained in the anhydrous form by all the usual methods, the most convenient being perhaps the action of chlorine and sulphur monochloride on the heated dioxide. It almost invariably contains small quantities of oxychloride. When pure, it forms colourless needles fairly stable in dry air; the impure product gradually darkens in colour. ”

“ It is readily decomposed by water anti) alkaline hydroxides, yielding a mixture of nitrite and chloride. On treatment with silver fluoride it yields nitrosyl fluoride, NOF (O. Ruff, Zeit. anorg. Chem., 1905, 47, p. 190) . Nitroxyl fluoride, NO2F, is formed by the action of fluorine on nitric oxide at the temperature of liquid oxygen (H. Moissan and P. Lebeau, Comptes rendus, 1905, 140, pp. 1573, 1621) . It is a gas at ordinary temperature; when liquefied it boils at −63.5° C. and on solidification melts at −139° C. Water decomposes it into nitric and hydrofluoric acids. ”

“ Using 5- or 10-mL syringes, filter each sample extract solution through a PTFE filter and a styrenebased sulfonic acid resin cartridge (follow the manufacturer’s instructions) , discard the first two milliliters and place the remaining solution in clean plastic vessels. CALIBRATION AND QUALITY CONTROL: 12.
With dilution of the calibration stock solution in eluent solution, prepare calibration working standard solutions covering the range of approximately 0.4 to 8 μg/mL of fluoride. Store working standards in tightly sealed polyethylene bottles. Prepare fresh working standards biweekly. 13. ”

“ Calibrate daily with at least six working standards over the range 3 to 1200 μg F per sample. a. Add known amounts of calibration stock solution to 25 mL TISAB and 5 mL 20% NaOH (particulate fluoride) or 25 mL TISAB (gaseous fluoride) in 100-mL beakers. b. Adjust pH to 5.5 ± 0.2 with 1:1 HCl. c. Transfer to 50-mL volumetric flasks. Dilute to the mark with deionized water. NOTE: Working standards are stable at least one month in polyethylene bottles at 4 °C. d. ”

“ Calcium fluoride, CaF2, constitutes the mineral fluor-spar (q.v.) , and is prepared artificially as an insoluble white powder by precipitating a solution of calcium chloride with a soluble fluoride. One part dissolves in 26,000 parts of water. Calcium chloride, CaCl2, occurs in many natural waters, and as a by-product in the manufacture of carbonic acid (carbon dioxide) , and potassium chlorate. Aqueous solutions deposit crystals containing 2, 4 or 6 molecules of water. ”

“ Salts of hydrofluoric acid,—fluorides. A number of the fluorides are known, but only one of them, calcium fluoride (CaF2) , is of importance. This is the well-known mineral fluorspar.
CHLORINE
Historical. While studying the action of hydrochloric acid upon the mineral pyrolusite, in 1774, Scheele obtained a yellowish, gaseous substance to which he gave a name in keeping with the phlogiston theory then current. Later it was supposed to be a compound containing oxygen. In [Pg 178] 1810, however, the English chemist Sir Humphry Davy proved it to be an element and named it chlorine. ”

“ Water gives hydrofluoric and phosphoric acids The corresponding sulphur compound, thiophosphoryl fluoride, PSF3, obtained by heating lead fluoride and phosphorus pentasulphide to 200°, is a colourless gas, which may be condensed to a clear transparent liquid. It spontaneously inflames in air or oxygen, and when the gas is issuing from a jet into air the flame is greyish green, with a faintly luminous and yellow tip ”

“ When the experiment is performed in the fluorspar tube, the gaseous fluoride may be collected over mercury. The gas fumes strongly in the air, and is instantly decomposed by water.
Silicon.—The reaction between fluorine and silicon is one of the most beautiful of all these extraordinary manifestations of chemical activity. The cold crystals become immediately white-hot, and the silicon burns with a very hot flame, scattering showers of star-like, white-hot particles in all directions. If the action is stopped before all the silicon is consumed, the residue is found to be fused. ”

“ A gaseous fluoride of sulphur is formed, which possesses a most penetrating odor, somewhat resembling that of chloride of sulphur. The gas is incombustible, even in oxygen. When warmed in a glass vessel, the latter becomes etched, owing to the formation of silicon tetrafluoride, SiF4. Selenium and tellurium behave similarly, but form crystalline solid fluorides.
Bromine vapor combines with fluorine in the cold with production of a very bright but low temperature dame. If the fluorine is evolved in the midst of pure dry liquid bromine, the combination is immediate, and occurs without flame. ”