October 29, 1891] 



NATURE 



625 



combines with more fluorine to form th3 pentafluoride, the 

 reaction being accompanied by the appearance of a flame 

 of comparatively low temperature. 



Arsenic combines with fluorine at the ordinary tem- 

 perature with incandescence. If the current of fluorine 

 is fairly rapid, a colourless fuming liquid condenses in the 

 receiver, which is mainly arsenic trifluoride, AsFg, but 

 which appears also to contain a new fluoride, the penta- 

 fluoride, AsFy inasmuch as the solution in water yields 

 the reactions of both arsenious and arsenic acids. 



Carbon —Q\Aox\'c\Q does not unite with carbon even at 

 the high temperature of the electric arc, but fluorine reacts 

 even at the ordinary temperature with finely-divided 

 carbon. Purified lampblack inflames instantly with great 

 brilliancy, as do also the lighter varieties of wood charcoal. 

 A curious phenomenon is noticed with wood charcoal : it 

 appears at first to absorb and condense the fluorine, then 

 quite suddenly it bursts into flame with bright scintilla- 

 tions. The denser varities of charcoal require warming 

 to 50^ or 60' before they inflame, but if once the combus- 

 tion is started at any point it rapidly propagates itself 

 throughout the entire piece. Graphite must be heated 

 to just below dull redness in order to effect combination ; 

 while the diamond has not yet been attacked by fluorine, 

 even at the temperature of the Bunsen flame. A mixture 

 of gaseous fluorides of carbon are produced whenever 

 carbon of any variety is acted upon by fluorine, the pre- 

 dominating constituent being the tetrafluoride, CF4. 



Boron.— T\\& amorphous variety of boron inflames 

 instantly in fluorine, with projection of brilliant sparks 

 and liberation of dense fumes of boron trifluoride, BF3. 

 The adamantine modification behaves similarly if 

 powdered. When the experiment is performed in the 

 fluor-spar tube, the gaseous fluoride may be collected over 

 mercury. The gas fumes strongly in the air, and is in- 

 stantly decomposed by water. 



Silicon.— ThQ reaction between fluorine and silicon is 

 one of the most beautiful of all these extraordinary mani- 

 festations 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. As crystalline silicon only melts at a tempera- 

 ture superior to 1200", the heat evolved must be very great. 

 If the reaction is performed in the fluor-spar tube, the 

 resulting gaseous silicon tetrafluoride, SiF4, may be 

 collected over mercury. 



Amorphous silicon likewise burns with great energy in 

 fluorine. 



ACTION OF FLUORINE UPON METALS. 

 Sodium a.r\d potassium combine with fluorine with great 

 vigour at ordinary temperatures, becoming incandescent, 

 and forming their respective fluorides, which may be ob- 

 tained crystallized from water in cubes. Metallic calcium 

 also burns in fluorine gas, forming the fused fluoride, and 

 occasionally minute crystals of fluor-spar. Thallium is 

 rapidly converted to fluoride at ordinary temperatures, the 

 temperature rising until the metal melts and finally 

 becomes red-hot. Powdered magnesium burns with 

 great brilliancy. Iron, reduced by hydrogen, combines 

 in the cold with immediate incandescence, and formation of 

 an anhydrous, readily soluble, white fluoride. Aluminium, 

 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 white- 

 ness. 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. Copper reacts at low redness, but in 

 a strangely feeble manner, and the white fumes formed 

 appear to combine with a further quantity of fluorine to 



NO. 1 148, VOL. 44] 



form a perfluoride. The main product is a volatile white 

 fluoride. Silver is only slowly attacked in the cold. 

 When heated, however, to 100", the metal commences to 

 be covered with a yellow coat of anhydrous fluoride, and 

 on heating to low redness combination occurs, with in- 

 candescence, and the resulting fluoride becomes fused, 

 and afterwards presents a satin-like aspect. Gold becomes 

 converted into a yellow deliquescent volatile fluoride when 

 heated to low redness, and at a slightly higher tempera- 

 ture the fluoride is dissociated into metallic gold and 

 fluorine gas. 



The action of fluorine on platinum has been studied 

 with special care. It is evident, in view of the corrosion 

 of the positive platinum terminal of the electrolysis ap- 

 paratus, that nascent fluorine rapidly attacks platinum at 

 a temperature of - 23°. At 100'', however, fluorine gas 

 appears to be without action on platinum. At 50o''-6do'' 

 it is attacked strongly, with formation of the tetra- 

 fluoride, PtF4, and a small quantity of the protofluoride, 

 PtF.,. If the fluorine is admixed with vapour of hydro- 

 fluoric acid, the reaction is much more vigorous, as if 

 a fluorhydrate of the tetrafluoride, perhaps 2HF.PtF4, 

 were formed. The tetrafluoride is generally found in the 

 form of deep-red fused masses, or small yellow crysta's 

 resembling those of anhydrous platinum chloride. The 

 salt is volatile and very hygroscopic. Its behaviour with 

 water is peculiar. With a small quantity of water a 

 brownish-yellow solution is formed, which, however, in a 

 very short time becomes warm and the fluoride decom- 

 poses ; platinichydrateisprecipitated,andfreehydrofluoric 

 acid remains in solution. 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, v/hich is evolved in the 

 free state. This reaction can therefore be employed as a 

 ready means of preparing fluorine, the fluoride only re- 

 quiring 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. 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 fluor-spar 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 pre- 

 paration of fluorine. 



ACTION OF FLUORINE UPON NON-METALLIC 

 COMPOUNDS. 



Sulphuretted hydrogen. — When the horizontal tube 

 shown in Fig. 3 is filled with sulphuretted hydrogen gas 

 and fluorine is allowed to enter, a blue flame is observed 

 on looking through the fluor-spar windows playing around 

 the spot where the fluorine is being admitted. The de- 

 composition continues until the whole of the hydrogen 

 sulphide is converted into gaseous fluorides of hydrogen 

 and sulphur. 



Sulphur dioxide is likewise decomposed in the cold, 

 with production of a yellow flame and formation of 

 fluoride of sulphur. 



Hydrochloric acid gz.% is also decomposed at ordinary 

 temperatures with flame, and, if there is not a large excess 

 of hydrochloric acid present, with detonation. Hydro- 

 fluoric acid and free chlorine are the products. 



Gaseous hydrobromic and hydriodic acids react with 

 fluorine in a similar manner, with production of flame 

 and formation of hydrofluoric acid. Inasmuch, however, 

 as bromine and iodine combine with fluorine, as previously 

 described, these halogens do not escape, but burn up to- 

 their respective fluorides. When fluorine is delivered 

 into an aqueous solution of hydriodic acid, each bubble 

 as it enters produces a flash of flame, and if the fluorine 

 is being evolved fairly rapidly there is a series of very 



