CXV
of the object. 435. Also the art of electro-gilding is a similar
application of the chemical effects of voltaic electricity. Iron
coated with zinc does not rust. 444.
§ 290. Chlorides, Iodides and Bromides are decomposed
in such a manner, that the metal appears at the negative,
Chlorine, Iodine and Bromine at the positive pole. Common salt
(Sodium chloride) may be very easily decomposed, but Sodium
does not appear at the negative pole, it combines with the Oxy
gen and Hydrogen of the water.
§ 291. b) The galvanic current also furthers chemical
composition. Pure zinc is not or only very slowly decomposed
in dilute sulphuric acid, if it is touched by a piece of silver it
oxidises. The relation between Galvanism and Chemistry has
led to
§ 292. c) The Electrochemical Theory of Davy and
Berzelius.
1) Just as copper and zinc are electrified by touching each
other, so the atoms of two elements in touching each other assume
opposite electricity and the attraction between their positive and
negative electricity is the cause of chemical combination. (Hence
chemical affinity is the inclination of atoms to be electrified
contrarily). This explains also the decompositions mentioned
above.
2) All elements may be arranged in such a manner, that
one of them by its being connected with the preceding one is
positively electrified.
3) Binate compounds which show negative electric pro
perties are called acids.
4) Also galvanic electricity is accompanied by chemical
decomposition and the strength of the electric current is pro
portional to the chemical decomposition (Faraday).
H*
