32 



KNOWLEDGE. 



[Februaby 1, 1898. 



into (lame, whilst charcoal burns with bright scintillations. 

 Only the diamond is able to resist this powerful solvent, to 

 which it does not succumb even at high temperatures. 

 The similar element, silicon, which can be obtained in a 

 crystalline form closely resembling the diamond, gives 

 a magnificent display in the presence of fluorine, the 

 crystals becoming white-hot and throwing showers of fiery 

 spangles in all directions. The heat is so intense that the 

 crystals melt, showing that their temperature has reached 

 one thousand two hundred degrees Centigrade. Phos- 

 phorus combines fiercely with fluorine. Prussian blue, on 

 account of the cyanogen it contains, burns with a beautiful 

 pink flame ; whilst from a crystal of iodine placed in 

 fluorine vapour a heavy liquid distils with a pale flame. 

 This liquid— an iodide of fluorine — etches glass, and if 

 thrown into water hisses like hot iron. The last-named 

 metal becomes white hot when exposed to fluorine ; even 

 iron-rust behaves in a similar manner. Nearly all 

 metals are raised to vivid incandescence in a current 

 of the gas, many appearing very beautiful, especially 

 aluminium and zinc. If the latter be slightly warmed 

 it bursts into a white flame too dazzling to gaze at or 

 describe. 



Although it has been known in various states of com- 

 bination for many years, having been first discovered by 

 Schwankhardt, of Nuremburg, in 1670, and rediscovered 

 by Scheele in 1771, fluorine was not obtained as fluorine 

 in the free state until about six years ago, when the French 

 chemist, Moissan, succeeded in isolating it by employing a 

 current of electricity from twenty-six or twenty-eight 

 Bunsen batteries. The current was passed through the 

 compound of fluorine and hydrogen known as hydro- 

 fluoric acid, which is similar to hydrochloric acid. To 

 improve the conductivity of the hydrofluoric acid it was 

 necessary to dissolve another fluorine compound in the 

 liquid. As will readily be imagined, it is not so difticult 

 to obtain free fluorine as to keep it when obtained. Every 

 part of the apparatus used by M. Moissan was made 

 of platinum, with screw joints and washers of lead, 

 which swell on contact with fluorine ; all the stoppers 

 being of fluor-spar. Fluorine has a powerful affinity for 

 silicon, one of the principal constituents of glass, so that 

 it was impossible to use glass vessels or tubes to contain 

 the gas. 



As regards the chemical nature of fluorine, it is a gas at 

 ordinary temperatures, and is the lightest member of the 

 series of elements containing chlorine, bromine, and 

 iodine. The attraction of fluorine for hydrogen exceeds 

 that of chlorine, and is so great that if a slow current of 

 fluorine gas be passed into a tube of fluor-spar containing 

 a drop of water, a dark fog is produced, which changes 

 presently to a blue vapour consisting of ozone— the con- 

 densed form of oxygen. The last-named substance appears 

 to be one of the few materials which has no affinity for 

 fluorine ; nothing is observed to take place between them 

 even when they are heated up to one thousand degrees 

 Fahrenheit. 



So far all experiments had been conducted with fluorine 

 gas, which, at the time it was isolated, resisted all attempts 

 to reduce it to the liquid state. Six years ago, however, 

 there was no laboratory — such as that at the Royal Insti- 

 tution — having powerful machinery for producing liquid 

 air or liquid oxygen, at the command of the investigator ; 

 in fact, liquid air itself was practically unknown. By the 

 aid of this weapon. Professors Dewar and Moissan have 

 succeeded in liquefying fluorine. At the extremely low 

 temperature of liquid oxygen it was found that fluorine 

 did not attack glass, and it was possible to use glass 

 vessels to hold the newly liquefied element. The appa- 



ratus consisted of a small glass bulb, E, fused to a 

 platinum tube. A, which contained another similar smaller 

 tube, D. Elach of the platinum inlet and outlet tubes, 

 B and C, was fitted with a screw valve, so arranged that at 

 any moment communication could be cut ofi', either with 

 the outer air or with the current of fluorine. The whole 

 of the little apparatus was placed in a cylindrical glass 

 vacuum vessel (not shown in the figure) containing liquid 

 oxygen, and connected with a vacuum pump and a mano- 

 meter. On entering, the fluorine gas passed into the 

 annular space and then down the tube, D, into the glass 

 bulb. At the temperature of boiling liquid oxygen 

 ( - 180° C.) the gas passed right through the apparatus, 

 but without attacking the glass. As 

 soon as the air pump was worked and 

 the liquid oxygen boiled vigorously, 

 a yellow mobile liquid — fluorine — was 

 seen condensing in the bulb. 



Although at this very low tempera- 

 ture ( - 185° C.) silicon, boron, carbon, 

 sulphur, phosphorus, and iron, pre- 

 viously cooled in liquid oxygen and 

 placed in the liquid fluorine, remained 

 unattacked, a fragment of frozen ben- 

 zene or oil of turpentine was acted 

 upon with great vigour, accompanied 

 by incandescence, showing that the 

 great affinity of fluorine for hydrogen 

 stUl remained. 



Professors Moissan and Dewar 

 noticed that if the liquid fluorine came 

 into contact with liquid oxygen two 

 layers were formed, the fluorine being 

 at the bottom. If the oxygen was not 

 quite dry they found that a white 

 iiocculent precipitate, which they be- 

 lieve to be an hydrate of fluorine, fell 

 to the bottom. This could be filtered 

 oti', and detonated violently as soon as 

 the temperature rose. 



From the experiments it was foimd 

 that the boiling point of fluorine is very SopieY,,.) 

 close to —187^0., being identical with 

 the boiling point of argon. This appears to be the first 

 example of two gaseous elements boiling at the same 

 temperature. 



By boiling the liquid oxygen surrounding the fluorine 

 at a very low pressure by the help of an air pump, the 

 temperature was lowered to -210° C, but the fluorine 

 showed no signs of solidifying. Nevertheless Moissan and 

 Dewar hope to produce a still lower temperature by 

 causing the liquid fluorine itself to boil vigorously at a low 

 pressure. 



The specific gravity of liquid fluorine was determined 

 by dropping in small pieces of solid bodies, including 

 wood, caoutchouc, etc., previously cooled in Uquid 

 oxygen. It was found that amber rose and fell in the 

 Uquid, so that the specific gravity of the liquid fluorine 

 must be about the same as that of amber, namely, 

 1-14. No specific absorption bands were visible in the 

 spectroscope. 



These experiments, which are more than interesting, 

 seem to show that there is no limit to the knowledge (of 

 the material universe at all events) that mankind may hope 

 to secure by patience and increase in mechanical skill, for 

 the work just described has been carried on within sixty- 

 three degrees of absolute zero, where, if our present 

 knowledge is of any worth, the life of the universe itself 

 would be extinguished. 



Apparatui- for Lique- 

 I'aitioii of Fluorine. 

 I From the Proceed- 

 in(/s of the Chemical 



