If the hydrofluoric acid contains a small quantity of water, either by accident or design, there is always disengaged at the positive pole ozone, which has no action on crystallized silicium.  In proportion as the water contained in the acid is thus decomposed, it is seen by the amperemeter that the conductivity of the liquid rapidly decreases.  With absolutely anhydrous hydrofluoric acid the current will no longer pass.  In many of our experiments we have succeeded in obtaining an acid so anhydrous that a current of 25 amperes was entirely arrested.

To render the liquid conducting, we have added before each experiment a small quantity of dried and fused fluorhydrate of fluoride of potassium.  In this case, decomposition proceeds in a continuous manner; we obtain at the negative pole hydrogen, and at the positive pole a regular disengagement of a colorless gas in which crystallized silicium in the cold burns with great brilliancy, becoming fluoride of silicium.  This latter gas has been collected over mercury, and accurately characterized.

Deville’s adamantine boron burns in the same manner, but with more difficulty, becoming fluoride or boron.  The small quantity of carbon and aluminum which it contains impedes the combination.  Arsenic and antimony in powder combine with this gaseous body with incandescence.  Sulphur takes fire in it, and iodine combines with a pale flame, losing its color.  We have already remarked that it decomposes cold water, producing ozone and hydrofluoric acid.

The metals are attacked with much less energy.  This is due, we think, to the small quantity of metallic fluoride formed preventing the action being very deep.  Iron and manganese in powder, slightly heated, burn with sparks.  Organic bodies are violently attacked.  A piece of cork placed near the end of the platinum tube, where the gas is evolved, immediately carbonizes and inflames.  Alcohol, ether, benzol, spirit of turpentine, and petroleum take fire on contact.

The gas evolved at the negative pole is hydrogen, burning with a pale flame, and producing none of these reactions.

When the experiment has lasted several hours, and there is not enough hydrofluoric acid left at the bottom of the tube to separate the two gases, they recombine in the apparatus in the cold, with violent detonation.

We have satisfied ourselves, by direct experiment, that a mixture of ozone and hydrofluoric acid produces none of the reactions described above.

It is the same with gaseous hydrofluoric acid.  Finally we may add that the hydrofluoric acid employed, as well as the hydrofluorate of fluoride, were absolutely free from chlorine.

The gas obtained in our experiments is therefore either fluorine or a perfluoride of hydrogen.

New experiments are necessary to settle this last point.  We hope soon to lay the results before the Academy.—­Comptes Mendus, vol. ciii., p. 202, July 19, 1886; Chem.  News.