770. Hydro-fluoric acid and fluorides.—­Solution of hydrofluoric acid did not appear to be decomposed under the influence of the electric current:  it was the water which gave way apparently.  The fused fluorides were electrolysed (417.); but having during these actions obtained fluorine in the separate state, I think it better to refer to a future series of these Researches, in which I purpose giving a fuller account of the results than would be consistent with propriety here[A].

[A] I have not obtained fluorine:  my expectations, amounting to conviction, passed away one by one when subjected to rigorous examination; some very singular results were obtained; and to one of these I refer at 1340.—­Dec. 1838.

771. Hydro-cyanic acid in solution conducts very badly.  The definite proportion of hydrogen (equal to that from water) was set free at the cathode, whilst at the anode a small quantity of oxygen was evolved and apparently a solution of cyanogen formed.  The action altogether corresponded with that on a dilute muriatic or hydriodic acid.  When the hydrocyanic acid was made a better conductor by sulphuric acid, the same results occurred.

Cyanides.—­With a solution of the cyanide of potassium, the result was precisely the same as with a chloride or iodide.  No oxygen was evolved at the positive electrode, but a brown solution formed there.  For the reasons given when speaking of the chlorides (766.), and because a fused cyanide of potassium evolves cyanogen at the positive electrode[A], I incline to believe that the cyanide in solution is directly decomposed.

[A] It is a very remarkable thing to see carbon and nitrogen in this case determined powerfully towards the positive surface of the voltaic battery; but it is perfectly in harmony with the theory of electro-chemical decomposition which I have advanced.

772. Ferro-cyanic acid and the ferro-cyanides, as also sulpho-cyanic acid and the sulpho-cyanides, presented results corresponding with those just described (771.).

773. Acetic acid.—­Glacial acetic acid, when fused (405.), is not decomposed by, nor does it conduct, electricity.  On adding a little water to it, still there were no signs of action; on adding more water, it acted slowly and about as pure water would do.  Dilute sulphuric acid was added to it in order to make it a better conductor; then the definite proportion of hydrogen was evolved at the cathode, and a mixture of oxygen in very deficient quantity, with carbonic acid, and a little carbonic oxide, at the anode.  Hence it appears that acetic acid is not electrolyzable, but that a portion of it is decomposed by the oxygen evolved at the anode, producing secondary results, varying with the strength of the acid, the intensity of the current, and other circumstances.