402 Sir Humphry Davy on the relations of 
reasonings may be applied to solutions of potassa, soda, &c. 
which do not chemically alter platinum by contact, and yet 
render it positively electrical with respect to platinum in water 
or saline solutions. It must however be called to mind that 
the oxygen in nitric acid, and the metals in the alkalies, have 
attractions of a very decided kind for platinum ; and in taking 
the scale of electro-negative bodies, solutions of chlorine, or 
nitro-muriatic acid, produce a more powerful electrical effect 
on platinum than nitric acid, nitric acid than muriatic, and 
muriatic than sulphuric. 
When platinum is brought in contact with an acid, the pole 
touching the acid is negative, the opposite pole is positive, as 
I have found by the condensing electrometer ; and the reverse 
is the case when it touches an alkali, so that the circulation 
of the electricity is from the metal to the alkali, and from the 
acid to the metal. 
Rhodium, iridium, and gold, act in combinations consisting 
of acid and alkali, on which they have no chemical effect, ex- 
actly like platinum ; the surface of the metal in the solution 
of alkali being positive, that in the solution of the acid, nega- 
tive. With silver and palladium the electricity is greater, 
particularly if nitric acid is used ; and with charcoal and oxi- 
dable metals, there is the same general result, the action 
being in general exalted in proportion as the chemical 
attractions are stronger, provided there are no interfering 
circumstances : and in combinations of this kind nitro-muri 
atic acid is more active than nitric, and the order is after, 
nitric, nitrous sulphuric, phosphoric, vegetable acids, sulphu- 
rous, prussic, sulphuretted hydrogen, and, with the alkalies, 
potassa, soda, baryta, ammonia, and so on. 
