98 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVII.) 
1931. It next becomes necessary to ascertain whether any true thermo current can 
be produced by electrolytes and metals, which can interfere with any electro-chemical 
effects dependent upon the action of heat. For this purpose different combinations 
of electrolytes and metals not acted on chemically by them, were tried, with the 
following results. 
1 932. Platinum and a very strong solution of potassa gave, as the result of many ex- 
periments, the hot platinum positive across the electrolyte to the cold platinum, pro- 
ducing a current that could deflect the galvanometer needle about 5°, when the tem- 
peratures at the two junctures were 60° and 240°. Gold and the same solution gave 
a similar result. Silver and a moderately strong solution, of specific gravity 10/0, 
like that used in the ensuing experiments (1948.) gave the hot silver positive, but 
now the deflection was scarcely sensible, and not more than 1°. Iron was tried in 
the same solution, and there was a constant current and deflection of 50° or more, 
but there was also chemical action (1948.). 
1933. I then used solution of the sulphur et of potassium (1812.). As already said, 
hot platinum is negative in it to the cold metal (1921.) ; but I do not think the action 
was thermo-electric. Palladium with a weaker solution gave no indication of a cur- 
rent. 
1934. Employing dilute nitric acid, consisting of one volume strong acid and fifty 
volumes water, platinum gave no certain indication : the hot metal was sometimes in 
the least degree positive, and at others an equally small degree negative. Gold in the 
same acid gave a scarcely sensible result ; the hot metal was negative. Palladium 
was as gold. 
1935. With dilute sulphuric acid, consisting of one by weight of oil of vitriol and 
eighty of water, neither platinum nor gold produced any sensible current to my gal- 
vanometer by the mere action of heat. 
1936. Muriatic acid and platinum being conjoined, and heated as before, the hot 
platinum was very slightly negative in strong acid : in dilute acid there was no sensible 
current. 
1937. Strong nitric acid at first seemed to give decided results. Platinum and 
pure strong nitric acid being heated at one of the junctions, the hot platinum became 
constantly negative across the electrolyte to the cold metal, the deflection being 
about 2°. When a yellow acid was used, the deflection was greater ; and when a 
very orange-coloured acid was employed, the galvanometer needle stood at 70 °, the 
hot platinum being still negative. This effect, however, is not a pure thermo current, 
but a peculiar result due to the presence of nitrous acid (1848.). It disappears al- 
most entirely when a dilute acid is used (1934.); and what effect does remain in- 
dicates that the hot metal is negative to the cold. 
1938. Thus the potash solution seems to be the fluid giving the most probable in- 
dications of a thermo current. Yet there the deflection is only 5°, though the fluid, 
being very strong, is a good conductor (1819.). When the fluid was diluted, and of 
