DEPENDENCE OF THE VOLTAIC CURRENT ON CHEMICAL ACTION. 
117 
produced will be in one direction, thus — - , through the part figured ; but if the 
metal be tin, the resulting current will be in the contrary direction, thus s-. 
2027. Strong and weak solutions of potassa being employed in the tubes, then the 
single metals zinc, lead, copper, tin, and cadmium (1981.), will produce a similar 
battery. 
2028. If the arrangement be as in fig. 13, in which the vessels 1, 3, 5, &c. contain 
strong sulphuric acid, and the vessels 2, 4, 6, &c. dilute sulphuric acid; and if the 
metals a, a , a, are tin, and b, b , b, are iron (1979.), a battery electric current will be 
produced in the direction of the arrow. If the metals be changed for each other, the 
acids remaining; or the acids be changed, the metals remaining; the direction of the 
current will be reversed. 
viii. Considerations of the sufficiency of chemical action. 
2029. Thus there are no want of cases in which chemical action alone produces 
voltaic currents (2017.) ; and if we proceed to look more closely to the correspondence 
which ought to exist between the chemical action and the current produced, we find 
that the further we trace it the more exact it becomes ; in illustration of which the 
following cases will suffice. 
2030. Chemical action does evolve electricity. — This has been abundantly proved by 
Becquerel and De la Rive. Becquerel’s beautiful voltaic arrangement of acid 
and alkali* is a most satisfactory proof that chemical action is abundantly sufficient 
to produce electric phenomena. A great number of the results described in the 
present papers prove the same statement. 
2031. Where chemical action has been, but diminishes or ceases, the electric current 
diminishes or ceases also. — The cases of tin (1882. 1884.), lead (1885.), bismuth (1895.), 
and cadmium (1905.), in the solution of sulphuretof potassium, are excellent instances 
of the truth of this proposition. 
2032. If a piece of grain tin be put into strong nitric acid, it will generally exert 
no action, in consequence of the film of oxide which is formed upon it by the heat 
employed in the process of breaking it up. Then two platinum wires, connected by 
a galvanometer, may be put into the acid, and one of them pressed against the piece 
of tin, yet without producing an electric current. If, whilst matters are in this posi- 
tion, the tin be scraped under the acid by a glass rod, or other non-conducting sub- 
stance capable of breaking the surface, the acid acts on the metal newly exposed, and 
produces a current ; but the action ceases in a moment or two from the formation of 
oxide of tin and an exhausted investing solution (1918.), and the current ceases with 
it. Each scratch upon the surface of the tin reproduces the series of phenomena. 
2033. The case of iron in strong nitric acid, which acts and produces a current at 
the first moment (1843. 1951. 2001.), but is by that action deprived of so much of its 
activity, both chemical and electrical, is also a case in point. 
* Annales de Chimie, 1827, xxxv. 122. Bibliotheque Universelle, 1838; xiv. 129, 171. 
