DIRECTION OF THE CURRENT AND OF CHEMICAL ACTION. 
119 
parallel, but separated by a drop of strong nitric acid at each extremity. Whilst in 
this state no current is produced in either apparatus ; but if a drop of water be added 
at b fig. 15., chemical action commences, and a powerful current is produced, though 
without metallic or any additional contact. To observe this with the apparatus, 
fig. 14., a drop of water was put in at b. At first there was no chemical action and 
no electric current, though the water was there, so that contact with the water did 
nothing: the water and acid were moved and mixed together by means of the end of 
the wire i ; in a few moments proper chemical action came on, the iron evolving 
nitrous gas at the place of its action, and at the same time acquiring a positive con- 
dition at that part, and producing a powerful electric current. 
2040. When the chemical action which either has or could have produced a current 
in one direction is reversed or undone, the current is reversed (or undone) also. 
2041. This is a principle or result which most strikingly confirms the chemical 
theory of voltaic excitement, and is illustrated by many important facts. Volta in 
the year 1802*, showed that crystallized oxide of manganese was highly negative to 
zinc and similar metals, giving, according to his theory, electricity to the zinc at the 
point of contact. Becquerel worked carefully at this subject in 1835'f~, and came 
to the conclusion, but reservedly expressed, that the facts were favourable to the 
theory of contact. In the following year De la Rive examined the subject^, and 
shows, to my satisfaction at least, that the peroxide is at the time undergoing che- 
mical change and losing oxygen, a change perfectly in accordance with the direction 
of the current it produces. 
2042. The peroxide associated with platinum in the green nitrous acid originates a 
current, and is negative to the platinum, at the same time giving up oxygen and con- 
verting the nitrous acid into nitric acid, a change easily shown by a common che- 
mical experiment. In nitric acid the oxide is negative to platinum, but its negative 
state is much increased if a little alcohol be added to the acid, that body assisting in 
the reduction of the acid. When associated with platinum in solution of potash, the 
addition of a little alcohol singularly favours the increase of the current for the same 
reason. When the peroxide and platinum are associated with solution of sulphuret of 
potassium, the peroxide, as might have been expected, is strongly negative. 
2043. In 1835 M. Munci<e§ observed the striking power of peroxide of lead to 
produce phenomena like those of the peroxide of manganese, and these M. de la 
Rive in 1836 immediately referred to corresponding chemical changes ||. M. Schcen- 
bein does not admit this inference, and bases his view of “ currents of tendency” on 
the phenomena presented by this body and its non-action with nitric acid^[. My own 
results confirm those of M. de la Rive, for by direct experiment I find that the 
* Annales de Chimie, 1802, xl. 224. t Ibid. 1835, lx. 164, 171. 
X Ibid. 1836, lxi. 40; and Bibliotheque Universelle, 1836, i. 152, 158. 
§ Bibliotheque Universelle, 1836, i. 160. || Ibid. 1836, i. 162, 154. 
Philosophical Magazine, 1838, xii. 226, 311 ; and Bibliotheque Universelle, 1838, xiv. 155. 
