MR. DANIELL ON VOLTAIC COMBINATIONS. 
109 
both upon local and current affinity ; and in the case before us I have little doubt that 
it is the affinity of the hydrogen thus tied down, as it were, to the surface of the plate 
which puts a stop to the decomposition of the water by the zinc. When a small 
quantity of nitric acid was added to the acidulated water, the same plate was entirely 
dissolved in a few hours without the extrication of any gaseous matter. It is probable 
that the elements of the nitric acid in this case acted by entering into combination 
with the hydrogen as it was evolved, and thus removing its opposing attraction. The 
decomposition also uninterruptedly proceeds when the hydrogen is evolved at a com- 
paratively remote point in the voltaic circuit. The well-known energy of gases in 
what is called their nascent state may be referred to the same cause, namely, their 
adhesion to the surfaces against which they are evolved, by which their elasticity is 
counteracted; much in the same way, and by the same species of force, that the so- 
luble gases are kept down by solution in water, and are enabled to exert their affini- 
ties for other forms of matter to advantage*. 
Of the strength of the affinity of hydrogen in this state we have abundant evidence 
in the facility with which it deoxidates the oxide of copper, when sulphate of copper 
is exposed to it, and precipitates the metal upon the negative plate of a voltaic cir- 
cuit. I shall also have occasion to prove to you in the course of this paper, that it 
is sufficient to deoxidate the oxide of zinc under similar circumstances ; and we see 
at once the impossibility of the oxidation of the metal proceeding in the presence of 
an agent capable of abstracting oxygen from it when already combined. 
When a metallic communication was made between the two plates of a cell in this 
its normal state, the evolution of hydrogen from the platinum was abundant, and at 
about the rate of three cubic inches in a quarter of an hour. 
Before I proceed to describe the principal series of experiments which I instituted 
with this apparatus, it may perhaps be worth while to point out the facility with 
which, by its means, some of the principles of the voltaic battery may be demon- 
strated, which are the most elementary, but at the same time the most difficult to 
illustrate. 
Taking one of the cells charged with water, acidulated with sulphuric acid, to 
which a small quantity of nitric acid has been added, its total inaction previous to 
the completion of the circuit is strongly contrasted with the torrents of gas which 
rise into the graduated jar placed over the platinum plate after the wires {p, q ) are 
* There is one well-known experiment which has given rise to much ingenious hypothesis, which may also 
receive its simplest explanation from the action of this force of heterogeneous adhesion, namely, the so-called 
metallization of ammonia. When mercury is made the negative electrode of a voltaic circuit in connexion with 
a strong solution of muriate of ammonia, hydrogen and ammoniacal gases are both evolved in contact with it : 
and not only does the adhesive force restrain the elasticity of the gases, but the latter also reacts upon the 
cohesion of the fluid metal, and causes it to expand and increase its volume in the manner which has been so 
often described. The results of the most careful examination of this amalgam by the first chemists are in 
entire conformity with this opinion. 
