by the Immersion of unequally Heated Metals in Liquids. 9 



proving the currents to be a result of a differential action be- 

 tween the plates, and not of a specific thermic action at the upper 

 plate. 



Influence of Chemical Action. 



27. To ascertain whether the currents under consideration 

 were solely due to chemical action, I examined several liquids in 

 the foregoing apparatus (7), using j^/a/mM»i plates to exclude, as 

 far as possible, chemical influences, and observed if any currents 

 were produced : the following are the particulars of the experi- 

 ments : — 



28. Took 4 ounces of distilled water, added to it a quarter 

 of an ounce of pure sulphuric acid, boiled the mixture in a glass 

 flask to ex-pel dissolved air, and cooled it in the closed flask ; 

 prepared the apparatus with extreme care, and when the liquid 

 was of the tempei-ature of the atmosphere, introduced it into the 

 cylinder; then tested the junction of the upper platinum plate 

 with its platinum connecting wire by heat, to ascertain if any 

 electric current could arise from the heat extending to the sol- 

 dered junction ; but no effect was produced, neither was there 

 any permanent deflection of the galvanometer needles produced 

 by any difference of cleanliness, temperature, smoothness or 

 otherwise, of the plates or washers. Steam being now passed 

 steadily into the cistern of water, the needles began to be deflected 

 immediately the thermometer indicated a rise in temperature, the 

 cold plate being positive ; and the deflection gradually increased 

 with the rise in temperature, being at 65° ¥. (the temperature 

 of the atmosphere and lower plate) ; 1'5 at 80°; 2 at 90°; 2'5 at 

 100°; 4 at 110°; 80 at 120°; 11-5 at 130°; 14-5 at 140°; 17-5 

 at 150°; 19-5 at 160°; 21 at 170°; 23 at 180°; 25 at 190°; 26 at 

 200° ; and 26-75 at 208° F. I then took a mixture of 4 ounces 

 of distilled water and a quarter of an ounce of pure nitric acid, and 

 performed a similar experiment ; the cold plate was again strongly 

 positive to the hot one, and increasingly with the increased dif- 

 ference of temperature. 



29. These currents did not arise from difference of chemical 

 action at the metallic surfaces, that being excluded by the careful 

 preparation of the plates, and proved by the previous quiescence 

 of the galvanometer; nor from chemical action developed by 

 heat, — 1st, because there was not the slightest sign of such action 

 upon either of the plates after either of the experiments ; and 

 2ndly, because if such action had occurred, the current produced 

 would have been in an opposite direction, as will hereafter be 

 proved in the present pa[jer. 



30. If a minute dctjree of chemical action is the cause of the 

 currents obtained witli ])latinuni plates, then I can at present 

 imagine with any reasonable degree of probability only the fol- 



