October 29, 1891] 



NATURE 



623 



pressed. During the electrolysis these leaden collars 

 become, where exposed to the gaseous fluorine, rapidly 

 converted into lead fluoride, which, being greater in bulk, 

 causes the joints to become hermetically sealed In order 

 to effect the electrolysis, 26 to 28 Bunsen elements are 

 employed, arranged in series. An ampere-meter and a 

 commutator are introduced between the battery and the 

 electrolysis apparatus ; the former affording an excellent 

 indication of the progress of the electrolysis. 



As the U-tube contains far more hydrofluoric acid than 

 can be used in one day, each lateral delivery-tube is fitted 

 with a metallic screw stopper, so that the experiments may 

 be discontinued at any time, and the apparatus closed. 

 The whole electrolysis vessel is then placed under a glass 

 bell-jar containing dry air, and kept in a refrigerator until 

 again required for use. In this way it maybe preserved full of 

 acid for several weeks, ready at any time for the preparation 



>fthe gas. Considerable care requires to be exercised 

 not to admit the vapour of methyl chloride into the U- 



ube, as otherwise violent detonations are liable to occur. 

 When the liquid methyl chloride is being introduced into 

 the cylinder, the whole apparatus becomes surrounded 

 with an atmosphere of its vapour, and as the platinum U- 

 tube is at the same instant suddenly cooled, the vapour is 

 liable to enter by the abducting tubes. Consequently, as 

 soon as the current is allowed to pass and fluorine is 

 liberated within the U-tube, an explosion occurs. Fluorine 

 instantly decomposes methyl chloride, with production of 

 flame and formation of fluorides of hydrogen and carbon, 

 liberation of chlorine, and occasionally deposition of car- 

 bon. In order to avoid this unpleasant occurrence, when 

 the methyl chloride is being introduced the ends of the 

 lateral delivery-tubes are attached to long lengths of 

 caoutchouc tubing, supplied at their ends with calcium 

 chloride drying tubes, so as to convey dry air from outside 

 the atmosphere of methyl chloride vapour. If great care 

 is taken to obtain the minimum temperature, this difficulty 

 may be even more simply overcome by employing a 

 mixture of well-pounded ice and salt instead of methyl 

 chloride ; but there is the counterbalancing disadvantage 

 to be considered, that such a cooling bath requires much 

 m ne frequent renewal. 



CHEMICAL REACTIONS OCCURRING DURING THE 

 ELECTROLYSIS. 



In the paper of 1887, M. Moissan adopted the view 

 that the first action of the electric current was to effect 

 the decomposition of the potassium fluoride contained in 

 solution in the hydrofluoric acid, fluorine being liberated 

 at the positive pole, and potassium at the negative ter- 

 minal. This liberated potassium would at once regenerate 

 potassium fluoride in presence of hydrofluoric acid, and 

 liberate its equivalent of hydrogen : 



KF = K + F. 

 K + HF= KF + H. 



But when the progress of the electrolysis is carefully 

 followed, by consulting the indications of the ampere- 

 meter placed in circuit, it is found to be by no means as 

 regular as the preceding formulae would indicate. With 

 the new apparatus, the decomposition is quite irregular 

 at first, and does not attain regularity until it has been 

 proceeding for upwards of two hours. Upon stopping 

 the current and unmounting the apparatus, the platinum 

 rod upon which the fluorine was liberated is found to be 

 largely corroded, and at the bottom of the U-tube a 

 quantity of a black, finely divided substance is observed, 

 'i his black substance, which was taken at first to be 

 metallic platinum, is a complex compound, containing 

 one equivalent of potassium to one equivalent of plati- 

 num, together with a considerable proportion of fluorine. 

 Moreover, the hydrofluoric acid is found to contain a 

 small quantity of platinum fluoride in solution The 

 electrolytic reaction is probably therefore much more 



NO, I 148, VOL. 44] 



complicated than was at first considered to be the case. 

 The mixture of acid and alkaline fluoride furnishes 

 fluorine at the positive terminal rod, but this intensely 

 active gas, in its nascent state, attaches the platinum and 

 produces platinum tetrafluoride, PtFj ; this probably 

 unites with the potassium fluoride to form a double 

 salt, possibly 2KF.PtF4, analogous to the well-known 

 platinochloride 2KCl.PtCl4; and it is only when the 

 liquid contains this double salt that the electrolysis pro- 

 ceeds in a regular manner, yielding free fluorine at the 

 positive pole, and hydrogen and the complex black 

 compound at the negative pole. 



PHYSICAL PROPERTIES OF FLUORINE. 



Fluorine possesses an odour which M. Moissan com- 

 pares to a mixture of hypochlorous acid and nitrogen 

 peroxide, but this odour is usually masked by that of the 

 ozone which it always produces in moist air, owing to its 

 decomposition of the water vapour. It produces most 

 serious irritation of the bronchial tubes and mucous 

 membrane of the nisal cavities, the effects of which 

 are persistent for quite a fortnight. 



When examined m a thickness of one metre, it is seen 

 to possess a greenish-yellow colour, but paler, and con- 

 taining more of yellow, than that of chlorine. In such a 

 layer, fluorine does not present any absorption-bands. 

 Its spectrum exhibits thirteen bright lines in the red, 

 between wave-lengths 744 and 623. Their positions and 

 relative intensities are as follows : — 



METHODS OF EXPERIMENTING WITH FLUORINE. 



When it is desired to determine the action of fluorine 

 upon a solid substance, the following method of pro- 

 cedure 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. 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. If the solid, phosphorus for instance, attacks 

 platinum, or the temperature of the reaction is sufficiently 

 high to determine the combination of platinum and 

 fluorine (towards 500"), a tube of fluor-spar is substituted 

 for the platinum tube. The fluor-spar tubes employed by 

 M. Moissan for the study of the action of phosphorus 

 were about twelve to fourteen centimetres long, and were 

 terminated by platinum ends furnished with flanges and 

 screw threads in order to be able to connect them with 

 the preparation apparatus. If it is required to heat the 

 fluor-spar tubes, they are surrounded by a closely wound 

 copper spiral, which may be heated by a Bunsen flame. 



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. When the liquid contains water, or when 



