Dec. 2 2, 1887] 



NATURE 



181 



gutta-percha, but the latter again soon melted on passing 

 the current, and was put hors de service. Gum-lac and 

 many other substances were tried, but all to no purpose, 

 and much precious time was lost. Finally, however, the 

 difficulty was overcome by using stoppers of fluor-spar, 

 carefully inserted in hollow cylinders of platinum carry- 

 ing fine screw threads upon their outer surfaces, which 

 engaged with corresponding threads upon the interior 

 surfaces of the two branches of the U-tube. The platinum 

 rods passed through the axis of each cylinder of fluor-spar : 

 the rods themselves were of square section, of 2 milli- 

 metres side and 12 centimetres long, and passed to 3 

 millimetres from the base of the (Jtube ; they were made 

 of irido-platinum, containing 10 per cent, iridium, which 

 is less attackable than pure platinum. The U-tube simply 

 consisted of a platinum tube, bent twice at right angles, 

 15 centimetre diameter and 9'5 centimetres high, and was 

 fitted with side tubes and immersed in methyl chloride as 

 before. 



The pure anhydrous hydrofluoric acid, which was the 

 next necessity, was prepared in the following manner. 

 A known volume of commercial acid was treated with 

 sufficient potassium carbonate to neutralize about a quar- 

 ter of it, and then distilled in a leaden retort over an oil 

 bath at 120°. At this temperature the fluosilicate of 

 potassium, formed from the hydrofluosilicic acid, con- 

 tained as impurity in the commercial acid, was not de- 

 composed, and the distillate was therefore free from silica. 

 This distillate was then divided into two parts, and one 

 half, saturated with pure potassium carbonate, forming 

 neutral potassium fluoride, was then added to the other 

 half, and transformed into HF . KF. The double fluoride 

 was then dried at 100°, and afterwards kept for some days 

 in the vacuous receiver of an air-pump, containing also 

 strong sulphuric acid and a few sticks of fused potash. 

 When absolutely dry it fell to powder, and was then 

 ready for the preparation of hydrofluoric acid, which was 

 always freshly prepared immediately before each experi- 

 ment. The dry fluoride was in each case introduced into 

 a recently ignited platinum retort, and maintained at a 

 moderate heat for some time so as to commence the de- 

 composition slowly ; the first portions of distillate were re- 

 jected, as they would contain the last traces of water. The 

 platinum receiver was then adapted and surrounded by 

 ice and salt ; on heating the retort more strongly, pure 

 hydrofluoric acid condensed in the receiver as a limpid 

 liquid boiling at I9°"4, very hygroscopic and fuming in 

 the air. 



While the preparation of the acid was in progress, the 

 U-tube and electrodes were drying at 120''. From 6 to 

 7 grammes of the dry double fluoride were now introduced 

 into the apparatus, the stoppers were screwed in and 

 covered with gum lac. The whole was then fixed in the 

 methyl chloride bath, and, until the introduction of the 

 acid, the delivery-tubes were connected with desiccators 

 containing fused potash. A constant supply of methyl 

 chloride at - 23° was maintained in the outer cylinder, as 

 a slight rise of temperature allowed of the volatilization 

 of some of the acid. About 15 to 16 grammes of the 

 anhydrous hydrofluoric acid were then gently aspirated 

 into the apparatus, and the current from twenty Bunsen 

 cells allowed to pass, when immediately a regular 

 evolution of gas occurred at each pole. At the negative 

 pole pure hydrogen was evolved, which burnt with its 

 characteristic flame, forming water. At the positive pole 

 was liberated a colourless gas of penetrating and very 

 disagreeable odour, somewhat resembling that of hypo- 

 chlorous acid, and rapidly irritating the mucous membranes 

 of the throat and eyes. It was no other than pure fluorine 

 itself. All the trouble, all the expense, and all the dis- 

 appointments were repaid. It must indeed have been a 

 supreme moment for M. Moissan. 



In order to study its action upon solids, they were 

 placed in small glass tubes, and brought near to the orifice 



of the platinum delivery-tube at the positive side. The 

 test was genera,lly repeated, holding the solids in small 

 platinum capsules. 



Sulphur, brought thus near the orifice, at once melted 

 and inflamed ; selenium behaved in like manner ; as did 

 also tellurium, with incandescence, forming fumes and 

 becoming coated with a solid fluoride. 



Phosphorus at once took fire, forming tri-, penta-, and 

 oxyfluorides. Powdered arsenic and antimony combined 

 with incandescence, the former yielding drops of AsFs. 



A fragment of iodine placed in the gas combined with 

 production of a pale blue flame; in an atmosphere of 

 iodine vapour fluorine itself burnt with a similar flame. 

 Vapour of bromine lost its colour and the combination 

 was sometimes accompanied by detonation. 



Cold crystalline silicon at once became incandescent, 

 and burnt with great brilliancy, sometimes with scintilla- 

 tions. On closing the little tubes containing it with the 

 thumb and opening under water, the silicon tetrafluoride 

 formed was absorbed and decomposed with precipitation 

 of silica. Any undecomposed silicon was found to have 

 been fused. 



Debray's adamantine boron also burnt in the gas, 

 becoming incandescent and giving off fumes. 



Fluorine has a most extreme affinity for hydrogen ; 

 they combine in the dark with explosion. In one of the 

 experiments the electrolysis was allowed to continue 

 several hours, so that eventually the small quantity of 

 undecomposed acid remaining in the U"tube was insuffi- 

 cient to keep the two gases apart ; the experimenters were 

 consequently suddenly startled by a violent detonation. The 

 hydrogen and fluorine had combined in the dark at the 

 low temperature of — 23°. The same detonation was 

 afterwards brought about on a smaller scale by reversing 

 the current. On bringing the wide-mouthed delivery-tube 

 of a hydrogen generator near the orifice, the detonation 

 at once occuired, and the hydrogen inflamed. 



Metals are all attacked with more or less energy by 

 fluorine, forming fluorides. Cold sodium and potassium 

 were at once rendered incandescent. Calcium, mag- 

 nesium, and aluminium acted similarly, in a more modi- 

 fied manner, becoming incandescent when slightly warmed. 

 Powdered iron and manganese, on gently warming, burnt 

 with bright scintillations ; lead was attacked in the cold, 

 and tin at a slightly elevated temperature. Mercury, as 

 suspected, entirely absorbed the gas, forming yellow proto- 

 fluoride. Silver at a gentle heat became coated with a 

 beautiful satin-like fluoride, soluble, unlike the chloride, in 

 water. Gold and platinum at 3oo''-40o° became coated 

 with their respective fluorides, which were decomposed 

 again at a red heat, with evolution of free fluorine. 



Perhaps the strongest evidence of the intense chemical 

 activity of fluorine is exhibited in its action upon cold 

 potassium chloride : the chlorine was at once expelled, 

 filling the air with its disagreeable odour, and was 

 identified by the usual chemical tests. Chlorine was 

 also expelled from its combination with carbon in 

 carbon tetrachloride. 



All organic compounds are violently attacked by 

 fluorine : a piece of cork at once carbonized and in- 

 flamed ; alcohol, ether, benzene, and turpentine took fire 

 immediately in contact with it. 



Glass, as might have been expected, is at once corroded 

 by fluorine ; some very delicate experiments were carried 

 out with perfectly dried glass, with the same result. 



Many other reactions, all interesting and all showing 

 the immense energy with which the atoms of fluorine are 

 endowed, were performed, but one especially ought to be 

 noticed, viz. the action of fluorine upon water. It is a 

 singular fact that, whenever oxygen is liberated in the cold, 

 there is a great tendency to form ozone : hence when 

 fluorine is attempted to be collected over water, the gas 

 collected is not fluorine, but ozonized oxygen ; water is 

 decomposed by the fluorine forming hydrofluoric acid, 



