Voltaic Circles produced by Acid and Alkaline Fluids, 491 



Time in hours. 



Milligrams of 

 silver deposited. 



Cubic centimetres of hydrogen at 0° 

 and 760 mm. 



Equivalent to silver. 



Actually collected. 



I. 8 



104 



10-8 



10-7 



J. 22 



76 



7-9 



7*8 



E. 16 



53 



5 5 



5-4 



L. 20 



36 



3 7 



3-6 



Various reducing agents were found ineffective in causing hydro- 

 gen evolution in this way ; thus no noticeable amount of hydrogen 

 was produced when sodium sulphite or hypophosphite, potassium 

 ferrocyanide, or manganous hydroxide and ammoniacal sal-ammoniac 

 were used. Similarly, no oxygen evolution was observed when a 

 mixture of sulphuric acid and barium dioxide, or hydrochloric acid 

 containing iodine in solution, was the acid fluid. On the other hand, 

 the oxygen absorbed by a platinum sponge aeration plate was suffi- 

 ciently active to cause some four times as much permanent current to 

 pass as was produced when a solid platinum plate was used immersed 

 some centimetres below the surface of the acid. 



By substituting various metals and caustic soda or ammonia solu- 

 tion for the platinum plate and alkaline solution containing a 

 reducing substance, tolerably energetic cells were obtained ; even in 

 the case of metals not ordinarily regarded as belonging to the oxi- 

 disable class, solution was readily brought about when the alkaline 

 fluid contained potassium cyanide.^ In all cases hydrogen was 

 evolved from the surface of the opposed platinum plate immersed in 

 sulphuric acid solution in quantity proportionate to the current 

 passing, whilst a quantity of metal was dissolved usually sensibly 

 equal to that representing the formation of the lowest oxide ; tin 

 dissolved to a somewhat less extent, indicating the production of 

 some stannic oxide, from 3 to 7 per cent, of the metal being dissolved in 

 this form, and the rest as stannous oxide ; and mercury dissolved to 

 form mercuric potassio-cyanide, 100 parts of metal dissolving for 

 108 of silver thrown down in the voltameter. Gold, silver, and 

 palladium readily evolved hydrogen when immersed in cyanide solu- 

 tion ; but platinum was ineffective, and iron gave only a faint action. 

 Thus the following figures were obtained in various experiments : — 



