by the Immersion of unequally Heated Metals in Liquids. 13 



liquid pre-boiled ; same result. These currents are of course 

 of a secondary character with regard to heat, being results of the 

 chemical action produced (or permitted) by the heat. 



39. That the currents are not due to secondary chemical action 

 is also evident ; for if they were, they would increase in quantity 

 with every increase of the primary chemical action, which is not 

 found to be the case, but the reverse ; the greater the amount 

 of chemical action in certain cases, the weaker are the results. 



Examination of Liquids. 



40. Having by means of platinum plates excluded, as far as 

 possible, all interference of chemical action, I now examined a 

 number of liquids in the apparatus with platinum plates. They 

 were all well filtered, and no visible appearance of chemical action 

 occurred in any case. 



41. Boracic Acid. — 4 ounces of distilled water and 60 grains 

 of boracic acid ; the solution was previously well boiled to expel 

 dissolved air ; the hot metal was negative to the cold one, the 

 current being upward through the liquid. 



42. Phosphoric Acid. — 4 ounces of distilled water and 55 

 grains of solid phosphoric acid, solution pre-boiled ; hot metal 

 negative. 



43. Sulphuric Acid. — 4 ounces of spring water and \ of an 

 ounce of pure sulphuric acid ; hot metal negative. Retried with 

 the liquid pre-boiled ; same result. Tried again with distilled 

 water and the liquid pre-boiled; same result. Using spring 

 water did not interfere with the conclusion sought in the case of 

 strongly acid or strongly alkaline liquids ; but with those solu- 

 tions which exhibited feeble acid or alkaline reaction, purity was 

 of importance, and previously boiling the liquid occasionally 

 reversed the electric relations of the metals. 



44. Hydrochluric Acid. — 4 ounces of spring water and ^ of an 

 ounce of pure hydrochloric acid; hot metal negative. Retried 

 the same liquid pre-boiled ; same result. Tried again with di- 

 stilled water and liquid pre-boiled ; same result. 



45. Nitric Acid. — 4 ounces of spring water and \ of an ounce 

 of pure nitric acid ; hot metal negative. Retried with liquid 

 pre-boiled ; same result. Tried again with distilled water and 

 liquid pre-boiled ; same result. 



46. Hydrocyanic Acid, — 4 ounces of distilled water pre-boiled, 

 and ^ of an ounce of ordinary hydrocyanic acid added ; hot 

 metal very feebly positive. Retried the same liquid after it had 

 absorbed some atmospheric air ; same result, but in a less degree. 

 It appeared probable, from the known chemical relations of cy- 

 anogen and cyanides to the noble metals, that slight chemical 

 action occurred in this case. 



