VOLTAIC EXCITATION AFFECTED BY TEMPERATURE. 
99 
specific gravity 1070, like that before used (1932.), the effect was only 1°, and cannot 
therefore be confounded with the results I have to quote. 
1939. The dilute sulphuric (1935.) and nitric acids used (1934.) gave only doubtful 
indications in some cases of a thermo current. On trial it was found, that the thermo 
current of an antimony-bismuth pair could not pass these solutions, as arranged in 
these and other experiments (1949. 1950.) ; that, therefore, if the little current obtained 
in the experiments be of a thermo electric nature, this combination of platinum and 
acid is far more powerful than the antimony-bismuth pair of Seebeck ; and yet 
that (with the interposed acid) it is scarcely sensible by this delicate galvanometer. 
Further, when there is a current, the hot metal is generally negative to the cold, 
and it is therefore impossible to confound these results with those to be described 
where the current has a contrary direction. 
1940. In strong nitric acid, again, the hot metal is negative. 
1941. If, after I show that heat applied to metals in acids or electrolytes which can 
act on them produces considerable currents, it be then said that though the metals 
which are inactive in the acids produce no thermo currents, those which, like copper, 
silver, &c. act chemically, may; then, I say, that such would be a mere supposition, 
and a supposition at variance with what we know of thermo-electricity ; for amongst 
the solid conductors, metallic or non-metallic (1867.), there are none, I believe, which 
are able to produce thermo currents with some of the metals, and not with others. 
Further, these metals, copper, silver, &c. do not always show effects which can be 
mistaken or pass for thermo electric, for silver in hot dilute nitric acid is scarcely 
different from silver in the same acid cold (1950.) ; and in other cases, again, the hot 
metal becomes negative instead of positive (1953.). 
Cases of one metal and one electrolyte ; one junction being heated. 
1942. The cases I have to adduce are far too numerous to be given in detail ; I will 
therefore describe one or two, and sum up the rest as briefly as possible. 
1943. Iron in diluted sulphuret of potassium. — The hot iron is well positive to the 
cold metal. The negative and cold wire continues quite clean, but from the hot iron 
a dark sulphuret separates, which becoming diffused through the solution discolours 
it. When the cold iron is taken out, washed and wiped, it leaves the cloth clean ; 
but that which has been heated leaves a black sulphuret upon the cloth when simi- 
larly treated. 
1944. Copper and the sulphuretted solution. — The hot copper is well positive to the 
cold on the first immersion, but the effect quickly falls, from the general causes 
already referred to (1918.). 
1945. Tin and solution of potassa. — The hot tin is strongly and constantly positive 
to the cold. 
1946. Iron and dilute sulphuric acid (1935.). — The hot iron was constantly positive 
o 2 
