INACTIVE CONDUCTING VOLTAIC CIRCLES, — ACIDS. 75 
ultimately stand firm as a proof against the theory of contact force, this will stand 
also. 
1847. I now used oxide of iron and platinum as the extremes of the solid part of the 
circuit, and the nitrous acid as the fluid; i. e. I heated the iron wire in the flame of a 
spirit-lamp, covering it with a coat of oxide in the manner recommended by Schcen- 
bein in his investigations, and then used it instead of the clean iron (1843.). The 
oxide of iron was at first in the least degree positive, and then immediately neutral. 
This circuit, then, like the former, gave no current at common temperatures ; but it 
differed much from it in conducting power, being a very excellent conductor of a 
thermo current, the oxide of iron not offering that obstruction to the passage of the 
current which the peculiar iron did (1843. 1844.). Hence scale oxide of iron and 
platinum produce no current by contact, the third substance in the proof circuit being 
nitrous acid ; and so the result agrees with that obtained in the former case, where 
that third substance was solution of sulphuret of potassium. 
1848. In using nitrous acid it is necessary that certain precautions be taken, founded 
on the following effect. If a circuit be made with the green nitrous acid, platinum 
wires, and a galvanometer, in a few seconds all traces of a current due to first dis- 
turbances will disappear ; but if one wire be raised into the air and instantly returned 
to its first position, a current is formed, and that wire is negative, across the electrolyte, 
to the other. If one wire be dipped only a small distance into the acid, as for instance 
one fourth of an inch, then the raising that wire not more than one eighth of an 
inch and instantly restoring it, will produce the same effect as before. The effect is 
due to the evaporation of the nitrous acid from the exposed wire (1937-). I may 
perhaps return to it hereafter, but wish at present only to give notice of the precau- 
tion that is required in consequence, namely, to retain the immersed wires undisturbed 
during the experiment. 
1849. Proceeding on the facts made known by Schgenbein respecting the relation 
of iron and nitric acid, I used that acid as the fluid in a voltaic circuit formed with 
iron and platinum. Pure nitric acid is so deficient in conducting power (1817.) that 
it may be supposed capable of stopping any current due to the effect of contact be- 
tween the platinum and iron ; and it is further objectionable in these experiments, be- 
cause, acting feebly on the iron, it produces a chemically excited current, which may 
be considered as mingling its effect with that of contact : whereas the object at pre- 
sent is, by excluding such chemical action, to lay bare the influence of contact alone. 
Still the results with it are consistent with the more perfect ones already described ; 
for in a circuit of iron, platinum, and nitric acid, the joint effects of the chemical action 
on the iron and the contact of iron and platinum, being to produce a current of a cer- 
tain constant force indicated by the galvanometer, a little chemical action, brought 
into play where the iron and platinum were in contact as before (1831.), produced a 
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