82 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVI.) 
now it must be assumed that the solution has acquired its first relation to the metals 
and to the sulphuret of lead, and gives an equilibrium condition of the contacts in 
the circle. 
18/3. So also with this sulphuretted solution and with potassa, dilution must, by 
the theory, be admitted as producing wo change in the character of the contact force; 
but with nitric acid it, on the contrary, must be allowed to change the character of the 
force greatly ( 1 977-)- So again acids and alkalies (as potassa) in the cases where cur- 
rents are produced by them, as with zinc and platinum for instance, must be assumed 
as giving the preponderance of electromotive force on the same side, though these are 
bodies which might have been expected to give opposite currents, since they differ so 
much in their nature. 
18/4. Every case of a current is obliged to be met, on the part of the contact ad- 
vocates, by assuming powers at the points of contact, in the particular case , of such 
proportionate strengths as will consist with the results obtained, and the theory is 
made to bend about (1956. 1992. 2006. 2014. 2063.), having no general relation for 
the acids or alkalies, or other electrolytic solution used. The result therefore comes 
to this : The theory can predict nothing regarding the results ; it is accompanied by 
no case of a voltaic current produced without chemical action, and in those asso- 
ciated with chemical action, it bends about to suit the real results, these contortions 
being exactly parallel to the variations which the pure chemical force, by experiment, 
indicates. 
18/5. In the midst of all this, how simply does the chemical theory meet, include, 
combine, and even predict, the numerous experimental results ! When there is a cur- 
rent there is also chemical action; when the action ceases, the current stops (1882. 
1885. 1894.) ; the action is determined either at the anode or the cathode, according 
to circumstances (2039. 2041.), and the direction of the current is invariably asso- 
ciated with the direction in which the active chemical forces oblige the anions and 
cations to move in the circle (962. 2052.). 
1876. Now when in conjunction with these circumstances it is considered, that the 
many arrangements without chemical action (1825, &c.) produce no current ; that 
those with chemical action almost always produce a current ; that hundreds occur 
in which chemical action without contact produces a current (201/, &c.) ; and that 
as many with contact but without chemical action (186/.) are known and are 
inactive ; how can we resist the conclusion, that the powers of the voltaic battery 
originate in the exertion of chemical force ? 
iii. Active circles excited by solution of sulphuret of potassium. 
1 877- In 1812 Davy gave an experiment to show, that of two different metals, 
copper and iron, that having the strongest attraction for oxygen was positive in oxi- 
dizing solutions, and that having the strongest attraction for sulphur was positive in 
