622 



NA TURE 



[October 29, 1891 



FURTHER RESEARCHES UPON THE 

 ELEMENT FLUORINE. 



SINCE the publication by M. Moissan of his celebrated 

 paper in the Ati?tales de Chimie et de Physique for 

 December 1887, describing the manner in which he had 

 succeeded in isolating this remarkable gaseous element, 

 a considerable amount of additional information has 

 been acquired concerning the chemical behaviour of 

 fluorine, and important additions and improvements have 

 been introduced in the apparatus employed for preparing 

 and experimenting with the gas. M. Moissan now 

 gathers together the results of these subsequent re- 

 searches — some of which have been published by him from 

 time to time as contributions to various French scientific 

 journals, while others have not hitherto been made known 

 — and publishes them in a long but most interesting paper 

 in the October number of the Annales de Chimie et de 

 Physique. Inasmuch as the experiments described are of 

 so extraordinary a nature, owing to the intense chemical 

 activity of fluorine, and are so important as filling a long 

 existing vacancy in our chemical literature, readers of 

 Nature will doubtless be interested in a brief account of 

 them. 



IMPROVED APPARATUS FOR PREPARING FLUORINE. 

 In his paper of 1887, the main outlines of which were 

 given in Nature at the time (1887, vol. xxxvii. p. 179),. 



This improved form of the apparatus is shown in the 

 accompanying figure (Fig. i), which is reproduced from 

 the memoir of M. Moissan. It consists essentially of 

 two parts — the electrolysis apparatus and the purifying 

 vessels. The electrolysis apparatus, a sectional view of 

 which is given in Fig. 2, is similar in form to that de- 

 scribed in the paper of 1887, but much larger. The U- 

 tube of platinum has a capacity of 160 c.c. It is fitted 

 with two lateral delivery tubes of platinum, as in the 

 earlier form, and with stoppers of fluor-spar, F, inserted 

 in cylinders of platinum, p, carrying screw threads, 

 which engage with similar threads upon the interior 

 surfaces of the limbs of the U-tube. A key of brass, 

 e, serves to screw or unscrew the stoppers, and between 

 the flange of each stopper and the top of each branch of the 

 U-tube a ring of lead is compressed, by which means 

 hermetic closing is effected. These fluor-spar stoppers,, 

 which are covered with a coatinj of gum-lac during the 

 electrolysis, carry the electrode rods, /, which are thus, 

 perfectly insulated. M. Moissan now employs electrodes 

 of pure platinum instead of irido-platinum, and the 

 interior end of each is thickened into a club shape in 

 order the longer to withstand corrosion. The apparatus 

 is immersed during the electrolysis in a bath of liquid 

 methyl chloride, maintained in tranquil ebullition at -23'. 

 In order to preserve the methyl chloride as long as- 

 possible, the cylinder containing it is placed in an outer 



M. Moissan showed that pure hydrofluoric acid readily 

 dissolves the double fluoride of potassium and hydrogen, 

 and that the liquid thus obtained is a good conductor of 

 electricity, rendering electrolysis possible. It will be re- 

 membered that, by passing a strong current of electricity 

 through this liquid contained in a platinum apparatus, 

 free gaseous fluorine was obtained at the positive pole 

 and hydrogen at the negative pole. The amount of 

 hydrofluoric acid employed in these earlier experiments 

 was about fifteen grams, about six grams of hydrogen 

 potassium fluoride, HF.KF, being added in order to render 

 it aconductor. Since the publication of that memoir a much 

 larmier apparatus has been constructed, in order to obtain 

 the gas in greater quantity for the study of its reactions, 

 and important additions have been made, by means of 

 which the fluorine is delivered in a pure state, free from 

 admixed vapour of the very volatile hydrofluoric acid. As 

 much as a hundred cubic centimetres of hydrofluoric acid, 

 together with twenty grams of the dissolved double 

 fluoride, are submitted to electrolysis in this new appa- 

 ratus, and upwards of four litres of pure fluorine is 

 delivered by it per hour. 



NO. I 148, VOL. 44] 



; glass cylinder containing fragments of calcium cblo^ride ; 



! by this means it is surrounded with a layer of dry air, a 

 bad conductor of heat. 



The purifying vessels are three in number. The first 

 consists of a platinum spiral worm-tube, of about 40 c.c> 

 capacity, immersed also in a bath of liquid methyl chloride, 

 maintained at as low a temperature as possible, about 

 -50°. As hydrofluoric acid boils at ig^'S (Moissan), 

 almost the whole of the vapour of this substance which is- 

 carried away in the stream of issuing fluorine is condenaedl 

 and retained at the bottom of the worm. To remove the 

 last traces of hydrofluoric acid, advantage is taken of the 

 fact that fused sodium fluoride combines with the free 

 acid with great energy to form the double fluoride HF.NaF, 



i Sodium fluoride also possesses the advantage of not 



i attracting moisture. After traversing the worm con- 

 denser, therefore, the fluorine is caused to pass through 

 two platinum tubes filled with fragments of fused sodium 

 fluoride, from which it issues in an almost perfect state of 

 purity. The junctions between the various parts of the 

 apparatus are effected by means of screw joints, between 

 the nuts and flanges of which collars of lead are com- 



