428 Mr. Arrott on some new 
incapable of producing this effect ; iodic, chloric, chromic, or, 
as in the beautiful arrangement of Becquerel, nitric acid, with 
an alkali, produce a powerful current, but in these cases the 
action is very different from that which takes place in simple 
neutralization of an acid by an alkali. 
I have observed, that a current is produced in many cases 
where, from the nature of the liquids, no current can be sup- 
posed to arise either from the union of an acid and an alkali, 
or from the action of the liquids on the metals employed.. 
Thus I found, that solutions of a per- and protosalt of iron, 
produced a current when they were allowed to touch each 
other, and also made to communicate by means of platina; 
the persalt becoming deoxidized and the protosalt oxidated. 
It seemed that in this case the current was due to the oxi- 
dation and deoxidation of the liquids, by means of the ele- 
ments of water which was decomposed, and it appeared pro- 
bable that, if substances were used capable of exerting a 
greater attraction for the oxygen and hydrogen, a propor- 
tionally greater effect would be obtained. With this view, 
I tried solution of chlorine, and found that the effect was very 
much increased. I next tried iodine in solution in water, and 
also in iodide of potassium: the effect was very feeble; and this 
is exactly what we ought to expect, for iodine has nearly an 
equal tendency to unite with oxygen and hydrogen, as appears 
from the mode in which it decomposes water. I was not 
aware at the time of making these experiments, that Schoen- 
bein had obtained the current from chlorine. 
We have an extremely simple and beautiful illustration of 
these actions in the case of salts of iron. If two tubes be 
stopped at one end with plaster of Paris, and filled one with 
per- and the other with protosulphate of iron, and both im- 
mersed in a vessel containing dilute sulphuric acid, on adding 
red prussiate of potash to the persalt, and sulphocyanide of 
potassium to the other, no change takes place ; but if we con- 
nect the two solutions by means of a slip of platina foil, we 
have instantly indications of the oxidation of the one, and de- 
oxidation of the other. I have also constructed an apparatus 
in the form of a battery, which, while it serves to illustrate the 
action in question, may, I think, prove both convenient and 
economical as an instrument of research in ordinary galvanic 
experiments. It consists of six small circular jars, within 
which are fixed tubes of baked clay, or porous earthenware. 
Small cylinders of platina foil, 06th inch diameter, and 1:5 
inch long, were placed in the porous tubes, and outside these 
larger cylinders of 1*8th inch diameter, and 1°5th inch lone. 
The whole was then formed into a series, by connecting the 
