624 



NA TURE 



[October 29, 1891 



hydrofluoric acid is a product of the reaction, cylinders 

 of platinum or of fluor-spar are employed. If it is re- 

 quired to collect and examine the product, the liquid is 

 placed along the bottom of a horizontal tube of platinum 

 or fluor-spar, as in case of solids, connected directly with 

 the preparation apparatus, and the product is collected 

 over water or mercury if a gas, or in a cooled platinum 

 receiver if a liquid. 



During the examination of liquids a means has acci- 

 dentally been discovered by which a glass tube may be 

 filled with fluorine gas. A few liquids, one of which is 

 carbon tetrachloride, react only very slowly with fluorine 

 at the ordinary temperature. By fiUing a glass tube with 

 such a liquid, and inverting it over a platinum capsule 

 also containing the liquid, \i is possible to displace the 

 liquid by fluorine, which, as the walls are wet, does not 

 attack the glass. Or the glass tube may be filled with 

 the liquid, and then the latter poured out, leaving the 

 walls wet; the tube may then be filled with fluorine gas, 

 which, being slightly heavier than air, remains in the 

 tube for some time. In one experiment, in which a glass 

 test-tube had been filled with fluorine over carbon tetra- 

 chloride, it was attempted to transfer it to a graduated 

 tube over mercury, but in inclining the test-tube for this 

 purpose, the mercury suddenly came in contact with the 

 fluorine, and absorbed it so instantaneously and with such 

 a violent detonation that both the test-tube and the 

 graduated tube were shattered into fragments. Indeed, 

 owing to the powerful affinity of mercury for fluorine, it 

 is a most dangerous experiment to transfer a tube con- 

 taining 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. 



For studying the action of fluorine on gases, a special 

 piece of apparatus, shown in Fig. 3, has been constructed. 



It is composed of a tube of platinum, fifteen centimetres 

 long, closed by two plates of clear, transparent, and 

 colourless fluor-spar, and carrying three lateral narrower 

 tubes also of platinum. Two of these tubes face each 

 other in the centre of the apparatus, and serve one for 

 the conveyance of the fluorine and the other of the gas 

 to be experimented upon. The third, which is of some- 

 what greater diameter than the other two, serves as exit- 

 tube for the product or products of the reaction, and 

 may be placed in connection with a trough containing 

 either water or mercury. The apparatus is first filled 

 with the gas to be experimented upon, then the fluorine 

 is allowed to enter, and an observation of what occurs 

 may be made through the fluor-spar windows. One most 

 important precaution to take in collecting the gaseous 

 products over mercury is not to permit the platinum 

 delivery-tube to dip more than two or at most three 

 millimetres under the mercury, as otherwise the levels of 

 the liquid in the two limbs of the electrolysis U-tube 



NO. I 148, VOL. 44] 



become so different owing to the pressure, that the 

 fluorine from one side mixes with the hydrogen evolved 

 upon the other, and there is a violent explosion. 



ACTION OF FLUORINE UPON THE NON-METALLIC 

 ELEMENTS. 



Hydrogen. — As just described, hydrogen combines 

 with fluorine, even at — 23" and in the dark, with explo- 

 sive force. This is the only case in which two elementary 

 gases unite directly without the intervention of extraneous 

 energy. If the end of the tube delivering fluorine is 

 placed in an atmosphere of hydrogen, a very hot blue 

 flame, bordered with red, at once appears at the mouth 

 of the tube, and vapour of hydrofluoric acid is produced. 



Oxygen. — Fluorine has not been found capable of 

 uniting with oxygen up to a temperature of 500^. On 

 ozone, however, it appears to exert some action, as will 

 be evident from the^following experiment. It was shown 

 in 1887 that fluorine decomposes water, forming hydro- 

 fluoric acid, and liberating oxygen in the form of ozone. 

 When a few drops of water are placed in the appa- 

 ratus shown in Fig. 3, and fluorine allowed to enter, 

 the water is instantly decomposed, and on looking through 

 the fluor-spar ends a thick dark cloud is seen over the 

 spot where each drop of water had previously been. 

 This cloud soon diminishes in intensity, and is eventually 

 replaced by a beautiful blue gas — ozone in a state of 

 considerable density. If the product is chased out by 

 a stream of nitrogen as soon as the dense cloud is 

 formed, a very strong odour is perceived, different from 

 that of either fluorine or ozone, but which soon gives 

 place to the unmistakable odour of ozone. It appears 

 as if there is at first produced an unstable oxide of 

 fluorine, which rapidly decomposes into fluorine and 

 ozone. 



Nitrogen and chlorine appear not to react with 

 fluorine. 



Sulphur. — In contact with fluorine gas, sulphur rapidly 

 melts and inflames. A gaseous fluoride of sulphur is 

 formed, which possesses a most penetrating odour, some- 

 what 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 vapour combines with fluorine in the cold with 

 production of a very bright but low-temperature flame. 

 If the fluorine is evolved in the midst of pure dry 

 liquid bromine, the corribination is immediate, and occurs 

 without flame. 



Iodine. — When fluorine is passed over a fragment of 

 iodine contained in the horizontal tube, combination 

 occurs, with production of a pale flame. A very heavy 

 liquid, colourless when free from dissolved iodine, and 

 fuming strongly in the air, condenses in the cooled receiver. 

 This liquid fluoride of iodine attacks glass with great 

 energy, and decomposes water when dropped into that 

 liquid with a noise like that produced by red-hot iron. 

 Its properties agree with those of the fluoride of iodine 

 prepared by Gore by the action of iodine on silver 

 fluoride. 



Phosphorus. — Immediately phosphorus, either the ordi- 

 nary yellow variety or red phosphorus, comes in contact 

 with fluorine, a most lively action occurs, accompanied by 

 vivid incandescence. If the fluorine is in excess, a fum- 

 ing gas is evolved, which gives up its excess of fluorine 

 on collecting over mercury, and is soluble in water. 

 This gas is phosphorus pentafluoride, PF.,, prepared 

 some years ago by Prof. Thorpe. If, on the contrary, 

 the phosphorus is in excess, a gaseous mixture of this 

 pentafluoride with a new fluoride, the trifluoride, PF3, 

 a gas insoluble in water, but which may be absorbed by 

 caustic potash, is obtained. The trifluoride, in turn, 



