112 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVII.) 
2007- That it cannot be an alteration of contact force by mere dilution at one side 
(2006.) is also shown by making such a change, but using metals that are chemically 
inactive in the electrolyte employed. Thus when nitric or sulphuric acids were di- 
luted at one side, and then the strong and the weak parts connected by platinum or 
gold (1976.), there was no sensible current, or only one so small as to be unimportant. 
2008. A still stronger proof is afforded by the following result. I arranged the 
tube, fig. 9 (1972.), with strong solution of yellow sulphuret of potassium (1812.) from 
A to m, and a solution consisting of one volume of the strong solution, with six of 
water from m to B. The extremities were then connected by platinum and iron in 
various ways ; and when the first effect of immersion was guarded against, including 
the first brief negative state of the iron (2049.), the effects were as follows. Platinum 
being in A and in B, that in A, or the strong solution, was very slightly positive, 
causing a permanent deflection of 2°. Iron being in A and in B, the same result was 
obtained. Iron being in A and platinum in B, the iron was positive about 2° to the 
platinum. Platinum being in A and iron in B, the platinum was now positive to the 
iron by about 2°. So that not only the contact of the iron and platinum passes for 
nothing, but the contact of strong and weak solution of this electrolyte with either 
iron or platinum, is ineffectual in producing a current. The current which is constant 
is very feeble, and evidently related to the mutual position of the strong and weak 
solutions, and is probably due to their gradual mixture. 
2009. The results obtained by dilution of an electrolyte capable of acting on the 
metals employed to form with it a voltaic circuit, may in some cases depend on 
making the acid a better electrolyte. It would appear, and would be expected from 
the chemical theory, that whatever circumstance tends to make the fluid a more 
powerful chemical agent and a better electrolyte, (the latter being a relation purely 
chemical and not one of contact,) favours the production of a determinate current. 
Whatever the cause of the effect of dilution may be, the results still tend to show how 
valuable the voltaic circle will become as an investigator of the nature of chemical 
affinity (1959.). 
f vi. Differences in the order of the metallic elements of voltaic circles. 
2010. Another class of experimental arguments, bearing upon the great question of 
the origin of force in the voltaic battery, is supplied by a consideration of the dif- 
ferent order in which the metals appear as electromotors when associated with dif- 
ferent exciting electrolytes. The metals are usually arranged in a certain order ; 
and it has been the habit to say, that a metal in the list so arranged is negative to 
any one above it, and positive to any one beneath it, as if (and indeed upon the con- 
viction that) they possessed a certain direct power one with another. But in 1812 
Davy showed inversions of this order in the case of iron and copper* (943.) ; and in 
1828 De la Rive showed many inversions in different cases'^ (1877-) ; gave a strong 
* Elements of Chemical Philosophy, p. 149. f Annales de Chimie, 1828, xxxvii. 232. 
