100 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



the same proportion as was evolved by the same current from water; and iodine with 

 out any oxygen was evolved at the positive electrode. But when diluted, small quan- 

 tities of oxygen appeared with the iodine at the anode, the proportion of hydrogen at 

 the cathode remaining undisturbed. 



768. I believe the decomposition of the hydriodic acid in this case to be direct, for 

 the reasons already given respecting muriatic acid (763. 764.). 



769. Iodides. — A solution of iodide of potassium being subjected to the voltaic cur- 

 rent, iodine appeared at the positive electrode (without any oxygen), and hydrogen 

 with free alkali at the negative electrode. The same observations as to the mode of 

 decomposition are applicable here as were made in relation to the chlorides when in 



solution {7^^)' 



770. Hydro-Jluoric acid and fluorides. — Solution of hydro-fluoric 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 electrolyzed (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. 



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 hydro-cyanic 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*, I incline to believe that the cyanide in solution is directly decomposed. 



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 water alone 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, 



* 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 de- 

 composition which I have advanced. 



