DETERMINING THE CONSTANTS OF A VOLTAIC CIRCUIT. 
315 
1 element required 30 turns. 
2 elements 61 turns. 
3 elements 91 turns. 
4 elements 120 turns. 
5 elements 150 turns. 
The electro-motive force of a circuit is therefore, as theory indicates, proportional 
to the number of similar elements of which it is formed, arranged in series. 
4. The next experiments were made to determine the amount of the contrary elec- 
tro-motive force which is introduced into a circuit when a voltameter or decomposing 
cell is interposed. The liquid in contact with the platinum electrodes was dilute 
sulphuric acid. The measure of this contrary electro-motive force is obtained by 
subtracting the actual number of turns from the number corresponding with the 
electro-motive force of the circuit when the decomposing cell is removed from it. 
3 elements with decomposing cell 21 turns 
4 elements with decomposing cell 50 turns 
5 elements with decomposing cell 7 9 turns 
6 elements with decomposing cell 109 turns 
Contrary electro- 
motive force. 
90 — 21 = 69 
120 - 50 = 70 
150 — 79 = 71 
180 — 109 = 70 
Mean 70 
The contrary electro-motive force may be considered therefore in this case to be 
constant, and to be to that of a single standard element as 7 : 3. It is hence obvious 
why three such elements are necessary to decompose water in a cell with platinum 
electrodes of a certain size, and charged with dilute sulphuric acid. The amount of 
this contrary force varies with different liquids, and according to the nature of the 
electrodes employed : as it is not my present object to investigate this subject, but 
merely to give a few examples of the measures which may be obtained by the above- 
mentioned method, I shall not enter on the consideration of these interesting but in- 
tricate modifications. 
5. The highest electro-motive force which a voltaic element consisting of two 
metals and one interposed liquid can manifest, is when the liquid is a solution of a 
salt of the negative metal, so that by the continual deposition of this metal the nega- 
tive surface is kept free from the contact of heterogeneous substances which would 
tend to give rise to a reverse current. When, in consequence of the chemical action, 
any heterogeneous solid matter is deposited on, or any evolved gas adheres to, the 
negative surface, the electro-motive force of the element is reduced. The following 
measures will show the reduction in electro-motive force of a zinc and copper, and of 
a zinc and platinum element, by substituting dilute sulphuric acid for the metallic salt ; 
the changes in these cases are effected by the adhesion of hydrogen to the surface 
of the negative metal. 
2 T 
MDCCCXLIII. 
