able difficulties occurred in executing the process. The liquid fluoric acid immediately destroys glass, and all animal and vegetable substances; it acts on all bodies containing metallic oxides; and I know of no substances which are not rapidly dissolved or decomposed by it, except metals, charcoal, phosphorus, sulphur, and certain combinations of chlorine.

I attempted to make tubes of sulphur, of muriates of lead and of copper containing metallic wires, by which it might be electrized, but without success. I succeeded, however, in boring a piece of horn silver in such a manner, that I was able to cement a platina wire into it, by means of a spirit lamp, and by inverting this in a tray of platina filled with liquid fluoric acid, I contrived to submit the fluid to the agency of electricity in such a manner, that in successive experiments it was possible to collect any elastic fluid that might be produced. Operating in this way, with a very weak Voltaic power, and keeping the apparatus cool by a freezing mixture, I ascertained that the platina wire at the positive pole rapidly corroded, and became covered with a chocolate powder; gaseous matter separated at the negative pole, which I could never obtain in sufficient quantities to analyze with accuracy; but it inflamed like hydrogen. No other inflammable matter was produced when the acid was pure.

In a case in which the acid had been condensed in a tube of lead, joined by a solder containing tin, a large quantity of powder separated at the negative surface of a dark colour, and which appeared to be tin mixed with a subfluate; the powder burnt when heated in the air, and gave fluoric fumes when treated by potassa and sulphuric acid.

I attempted to electrize the liquid fluoric acid, by making plumbago the positive surface; but the plumbago was quickly destroyed, a subfluate of iron was deposited on the negative surface, and the liquid became turbid and black. When a point of charcoal attached to a wire of platina was made positive, the effects were similar to those produced by a platina wire alone, for the acid speedily penetrated through the pores of charcoal, and the platina, in consequence, became a point of contact with the fluid.

I applied the power of the great Voltaic batteries of the Royal Institution to the liquid fluoric acid, so as to take sparks in it. In this case, gas appeared to be produced from both the negative and the positive surfaces; but it was probably only the undecompounded acid rendered gaseous, which was evolved at the positive surface, for during the operation the fluid became very hot, and speedily diminished. The manner in which the surrounding atmosphere became filled with the fumes of the fluoric acid, rendered it, indeed, very difficult to examine the results of any of these experiments; the dangerous action of these fumes have been described by M. M. GAY LUSSAC and THENARD, and I suffered considerable inconvenience from their effects during this investigation. By mere exposure to them in their uncondensed state, my fingers became sore beneath the nails, and they produced a most painful sensation, which lasted for some hours, when they came in contact with the eyes.

The phenomena of the Voltaic electrization of fluoric acid, present no evidences in favour of its containing a peculiar combustible substance and oxygen; and the most simple mode of explaining them, is by supposing the fluoric acid, like

muriatic acid, composed of hydrogen, and a substance, as yet unknown, in a separate form, possessed, like oxygen and chlorine, of the negative electrical energy, and hence determined to the positive surface, and strongly attracted by metallic sub

stances.

This view is much more conformable to the general order of chemical and electrical facts than the third hypothesis, just now mentioned.

It is indeed possible to conceive, if the metals be regarded as compounds of hydrogen, that the hydrogen may be produced from the metal, positively electrified at the time that the acid combines with its supposed basis, and that this hydrogen may be transferred to the negative surface; but this supposition involves a multitude of others; and the results of the electrization of fluoric acid are analogous to most of the results of the electrization of water and muriatic acid, both of which are shewn by analysis and synthesis to be compounds of hydrogen; and in the electrical decomposition of these bodies, their characteristic element is generally combined with the positive metallic surface.

In the Bakerian Lecture for 1810, I have given an account of the action of potassium upon pure silica. In this process, the potassium acquires oxygen, and a combustible substance, which consists either of the basis of silica, or the basis of silica combined with potassium appears. In supposing the silicated fluoric acid gas to be composed of this basis and the fluoric principle, it is easy to explain the action of potassium upon it, and the complicated phenomena, occasioned by the agency of water, and acids, and oxygen, on the results of this action. The potassium must be conceived to attract a part of the fluoric

́principle from the siliceous basis, or to form a triple compound, from which silicated fluoric acid gas is capable of being reproduced, in consequence of the combination of a part of the potassium and siliceous basis with oxygen; and on this idea the cause of the apparent loss of the fluoric principle, in the experiments on the action of ammonia on the product of the combustion of potassium in silicated fluoric acid gas, becomes obvious.

Assuming then from the analogy with chlorine, that the different fluoric compounds consist of inflammable bodies united to a peculiar principle, it follows that all attempts to decompose the fluoric acids, by combustible substances, can lead to no other result, than that of occasioning new combinations of the fluoric principle; and the only methods which seemed plausible for obtaining this principle pure, after that by electrical decomposition had failed, were by the action of oxygen or chlorine on certain of its compounds. Chlorine is, in certain instances, detached from hydrogen by oxygen; and oxygen, in a number of cases, is detached from metals by chlorine; I thought it therefore probable, that the fluoric principle might, in some process, be separated from bases by either chlorine or oxygen.

In selecting compounds for experiments of this kind, I was guided by the relative attractions of the fluoric and muriatic acids, of chlorine and oxygen. Horn silver and calomel, and muriate of potassa are not decomposed by fluoric acid, but fluate of silver, of mercury, and of potassa are easily decomposed by muriatic acid; I therefore conceived, that the fluoric principle would most likely be expelled from the dry fluates of silver, mercury, and potassa by chlorine.

I made some pure fluates of silver and mercury, by dissolving the oxides of these metals in fluoric acid, and I heated them in small trays of platina; much fluoric acid was driven off in this process, which I continued in the case of the fluate of mercury till the salt began to sublime, and in that of the fluate of silver till it was red hot.

The dry salts were introduced in small quantities into glass retorts, which were exhausted and then filled with pure chlorine: the part of the retort in contact with the salt was heated gradually till it became red. There was soon a strong action, the fluate of mercury was rapidly converted into corrosive sublimate, and the fluate of silver more slowly became horn silver. In both experiments there was a violent action upon the whole of the interior of the retort. On examining the results, it was found that in both instances there had been a considerable absorption of chlorine, and a production of silicated fluoric acid gas, and oxygen gas.

I tried similar experiments, with similar results, upon dry fluates of potassa and soda. By the action of a red heat, they were slowly converted into muriates with the absorption of chlorine, and the production of oxygen, and silicated fluoric acid gas, the retort being corroded even to its neck.

The obvious explanation of these phenomena is, that a particular principle, the acidifying matter of the fluoric acid, combined with the metals, is expelled from them by the stronger attraction of the chlorine, and that this principle coming in contact with glass decomposes it by its attraction for the silicum and sodium, and separates them from the oxygen with which they were combined.

I made various attempts to procure the fluoric principle in a