38 
MR. BIRD ON THE ELECTRO-CHEMICAL INFLUENCE OF 
rally deposited from its solution on the platinum plate in a more or less crystalline 
form. M. Becquerel did not attribute the reduction of the metal to the electric 
current alone, but conceived that three distinct causes, at least, concurred in pro- 
ducing this effect. The decomposition of the water and of the common salt by the 
electric current set in motion, and the transference of hydrogen and soda through 
the clay diaphragm to the negative tube, where the alkali unites with the acid hold- 
ing the metal in solution, causing the deposition of its oxide, which, while in its 
nascent state, is reduced by the hydrogen, and precipitated in its metallic form on 
the negative electrode ; thus regarding the hydrogen furnished by the decomposition 
of the water as the actual reducing agent. In some cases, a fourth cause is supposed 
to be superadded to these, as when a body is used for the negative electrode, for 
which the metal in solution has a certain degree of affinity ; a well-known example 
of which is found in the reduction of potassium from a solution of potassa when sub- 
mitted to comparatively weak voltaic action in contact with mercury. Mercury is 
not the only metal applicable to this purpose, M. Becquerel having frequently used 
iron with success. He states that the solutions of the pure chlorides of zirconium, 
glucium, titanium, silicon, &c., refused to yield to the reducing action of weak elec- 
tric currents, until after the addition of a small quantity of chloride of iron : this the 
current readily decomposed, precipitating the iron in a crystalline form on the plati- 
num plate, (negative electrode,) which deposit speedily induces the commencement of 
the decomposition of the more refractory salts. This circumstance he attributes to 
the affinity of the iron for the other metal tending to the formation of an alloy, and 
expressly states, that when perfectly pure the above-mentioned chlorides did not un- 
dergo the slightest decomposition. I have ascertained, however, that if the electric 
current is continuous, notwithstanding its weak tension, this reduction and decompo- 
sition may be effected without the presence of iron, or indeed of any other metal in 
solution, excepting that which we are attempting to reduce. I must apologize for 
the above rapid sketch of some of M. Becquerel’s researches, the introduction of 
which into this paper appeared to be necessary for the better understanding the re- 
sults of my own more limited investigations. 
3. On commencing my experiments on the chemical power of electric currents of 
weak tension, I soon found the want of an apparatus capable of affording an equal 
and continuous current of low intensity, which appeared to me to be absolutely neces- 
sary for the success of my experiments. In the common electromotor the currents 
are at first very energetic, but soon cease, or become so feeble as to be scarcely able 
to traverse a fluid medium unless fresh portions of the exciting fluid is added from 
time to time. Even Professor Daniell’s very ingenious single-pair battery, although 
most excellent for electro-magnetic purposes, and affording considerable quantities 
of electricity, yet required the occasional addition of fresh acid and sulphate of cop- 
per, which was inconvenient when required to be kept in constant action for some 
weeks, besides occasioning an irregularity in the intensity of the current. The quan - 
