336 



Mr. G. Gore on the Thermo-electric [Feb. 23, 



of sodium (strong solution) ; tribasic phosphate of sodium ; nitrate, chlo- 

 ride, and chlorate of potassium ; bromide of potassium (strong solution) ; 

 iodide of potassium (strong solution) ; carbonate, acid carbonate, and bi- 

 chromate of potassium ; aqueous ammonia ; chloride of ammonium ; cya- 

 nide and ferrocyanide of potassium ; acetate of zinc ; and acetate of sodium. 

 And negative in the following ones : — nitric, chloric, hydrobromic, hydro- 

 fluosilicic, and sulphuric acids ; ferrous sulphate ; chloride of copper (strong 

 solution) ; sulphate of copper ; sulphate of zinc (strong solution) ; nitrate 

 and iodide of sodium (weak solutions) ; bromide and iodide of potassium 

 (weak solutions) ; iodate of potassium ; chrome alum ; nitrate of ammo- 

 nium ; oxalic, acetic, tartaric, and citric acids. The number of liquids in * 

 which hot copper was positive was thirty-six, and of those in which it was 

 negative was twenty. 



In several instances where the hot metal was negative with a weak solu- 

 tion, it became positive with a strong one — for instance, with sulphate of 

 zinc, nitrate, iodide, and sulphate of sodium, bromide and iodide of potas- 

 sium ; but with chloride of copper the reverse occurred. These results 

 may be connected with the fact that in weak neutral solutions the chemical 

 action is generally the most feeble, and therefore interferes the least with 

 the direct influence of the heat in producing electric currents. 



The influence of free hydrochloric, hydrocyanic, boracic, orthophosphoric, 

 and chromic acids was to make the hot copper positive ; whilst that of 

 nitric, chloric, hydrobromic, hydrofluosilicic, sulphuric, and some of the 

 organic acids was to make it negative. 



In consequence, probably, of the small amount of interference by che- 

 mical action in solutions of oxalic, acetic, tartaric, and citric acids, the 

 direct influence of the heat made the copper negative — similar to its influ- 

 ence on platinum in all acid liquids which do not attack that metal. 



The nature of the acid in a salt appears to exert much more influence 

 than that of the base on the direction of the current; for instance, in 

 nearly all chlorides, including those of a considerable variety of bases, hot 

 copper was positive, probably because copper is more readily attacked by 

 acids than by bases. 



In all decidedly alkaline liquids the hot copper was positive ; this is 

 similar to the behaviour of platinum in such solutions, and is probably due 

 to the same cause, viz. the direct influence of the heat, as well as to che- 

 mical action. 



The results also show that the quantity of the current obtained with any 

 given liquid generally increases with the number of molecules of the sub- 

 stance contained in the solution ; in some cases, however, as with sulphuric 

 acid, carbonate of potassium, chloride of ammonium, and acetate of zinc, 

 there was a limit to this increase ; and beyond that limit the quantity of 

 the current decreased up to the point of saturation of the liquid. 



In the great majority of cases the value of the deflection increased much 

 more rapidly than the strength of the solution, particularly with solutions 



