Metallic Salts by an Electric Current. 215 



III. Hydrochloric acid, 3 to 12 of water, current passing 

 for twenty-four hours, — 



Deposited upon the negative electrode 47 grs. 



Dissolved from the positive electrode . 87 ... 



Zinc dissolved in the battery . . . 50 ... 

 Similar experiments were made with the positive division 

 charged with a solution of chloride of sodium, chloride of po- 

 tassium, chloride of ammonium and several other chlorides, 

 in the whole of which there was more dissolved from the po- 

 sitive electrode than was deposited on the negative. Witii 

 dilute sulphuric acid, sulphate of copper, or any of the soluble 

 sulphates, in the positive division, the quantity deposited was 

 exactly equivalent to that dissolved from the positive, except 

 where the current was continued for several days, when the 

 positive electrode was slightly covered with a black gelatinous 

 substance, supposed by some to be oxide of copper, formed 

 from an imperfect transfer of the sulphuric acid, which leaves 

 it undissolved ; but in such cases I have always found an equi- 

 valent of copper held in solution to that deposited, this black 

 matter being also formed. I do not refer here to the black 

 matter which is a constant attendant when impure copper 

 or salts of copper are used, and which is in a great measure 

 caused by the iron in the salt or in the metal forming the 

 electrode. When the nitrates were used in the positive 

 division, the results were the same as with the sulphates, and 

 when long continued, a little brownish matter was formed on 

 the positive electrode, and there was consequently more dis- 

 solved from the positive than was deposited on the negative. 



When 1 part of nitric acid was used to 12 of water, there 

 was nearly one-fourth more dissolved from the positive than was 

 deposited upon the negative, although a piece of copper put 

 into acid of the same strength and for the same length of time 

 as the battery was in action, was not perceptibly acted upon. 

 Other phaenomena were observed during these experiments, 

 which I shall take occasion to notice on a future opportunity, 

 but will now offer a few general remarks upon the results de- 

 tailed. In the first place it may be stated generally, that 

 when the double cyanides are the electrolytes, the amount of 

 metal liberated at the cathode and dissolved from the anode 

 is not in equivalent proportions, but varies according to their 

 relative size and the condition of the solution; when the solu- 

 tions are neutral, there is a tendency in favour of more being 

 deposited upon the cathode than is dissolved from the anode, 

 even when they are equal in size ; and when there is an ex- 

 cess of cyanide of potassium, the tendency is great for the so- 

 lution of more from the positive than what is deposited on the 



