by the Immersion of unequally Heated Metals in Liquids. 11 



usually obtained with platinum plates do not arise from a small 

 amount of chemical affinity developed at the upper surface by 

 the action of heat, whilst with some metals, where we know 

 such affinity to exist, they show that the strength of the cur- 

 rents of the other cause is influenced by it. The examiner, fitted 

 with a copper plate below and a platinum one above, was charged 

 with a solution composed of 100 grains of sulphate of copper 

 dissolved in 4 ounces of distilled water, the liquid being pre- 

 boiled ; on connecting with the galvanometer there was a per- 

 manent deflection of 31 degrees, arising from difi^erence of che- 

 mical action of the liquid upon the two metals, the copper being 

 of course positive; this deflection was gradually increased to 57 

 degrees by heating the platinum plate to 208° F., the lower 

 plate being at 64° F. The copjier plate was quite clean and bright 

 after the experiment. The apparatus was now fitted with the pla- 

 tinum plate below and the copper one above, and recharged with 

 the same liquid (previously cooled) ; the deflection from difi'er- 

 ence of chemical action was 33 degrees, the copper plate being of 

 course positive; this deflection was gradually decreased to 22 

 degrees by heating the copper plate to 208° F., the lower plate 

 being at 63° F. The copper plate was distinctly blackened by the 

 chemical action. 



34. In the first of these experiments the undetermined 

 cause gave an increased negative condition to the upper plate 

 = 26 degrees ; but in the second, the decreased positive con- 

 dition of the upper plate due to this tendency or cause was only 

 equal to 11 degi-ees (and those degrees of less value than in the 

 first case, owing to the nearer position of the needles to zero), 

 which I attribute to the chemical action at the upper plate tend- 

 ing to excite a feeble electric current in an opposite direction, or 

 in other words, tending to make that plate more positive. The 

 various precautions already described were taken in order to 

 secure reliable comparative results. 



35. I further tried this with plates of copper and silver, and a 

 solution composed of 10 ounces of water and 220 grs. of sulphate 

 of copper ; with the copper plate below and the silver one above 

 there was a permanent steady deflection of 52 degrees from dif- 

 ference of chemical action of the liquid upon the two metals (cop- 

 per positive), which was gradually increased to 69 degrees by heat- 

 ing the silver plate to 207° F., the lower plate being at 70° F. The 

 silver plate was very slightly tarnished after the experiment. The 

 apparatus was now fitted with the copper plate above and the 

 silver one below, and charged as before ; the deflection from dif- 

 ference of chemical action was 52|^ degrees, which was gradually 

 decreased to 41 degrees by heating the copper plate to 208° F., 

 the Hilver plate and lower part of the liquid being at 75° F. The 



