284 Faraday's Researches

zinc, hot zinc is a little positive, cold zinc much more so. With
silver and lead, the hot silver is a little positive to the lead, the
cold silver is more, and well positive. In these cases the current
is preceded by a moment of quiescence (941), during which the
chemical action at the hot metal reduces the efficacy of the
electrolyte against it more than at the cold metal, and the
latter afterwards shows its advantage.

955. Before concluding these observations on the effects of
heat, and in reference to the probable utility of the voltaic
circuit in investigations of the intimate nature of chemical
affinity (947), I will describe a result which, if confirmed, may
lead to very important investigations. Tin and lead were con-
joined and plunged into cold dilute sulphuric acid; the tin was
positive a little. The same acid was heated, and the tin and
lead, having been perfectly cleaned, were reintroduced, then the
lead was a little positive to the tin. So that a difference of
temperature not limited to one contact, for the two electrolytic
contacts were always at the same temperature, caused a differ-
ence in the relation of these metals the one to the other. Tin
and iron in dilute sulphuric acid appeared to give a similar result;
i.e. in the cold acid the tin was always positive, but with hot
acid the iron was sometimes positive. The effects were but
small, and I had not time to enter further into the investigation.

956. I trust it is understood that, in every case, the pre-
cautions as to very careful cleansing of the wires, the places
of the ends, simultaneous immersion, observation of the first
effects, etc., were attended to.

^f v. The Exciting Chemical Force affected by Dilution

957. Another mode of affecting the chemical affinity of these
elements of voltaic circuits, the metals and acids, and also
applicable to the cases of such circuits, is to vary the proportion
of water present. Such variation is known, by the simplest
chemical experiments, to affect very importantly the resulting
action, and, upon the chemical theory, it was natural to expect
that it would also produce some corresponding change in the
voltaic pile. The effects observed by Avogadro and QErsted
in 1823 are in accordance with such an expectation, for they
found that when the same pair of metals was plunged in suc-
cession into a strong and a dilute acid, in certain cases an in-lead and tin, the