Electrolysis of Secondary Compounds. 185 



*' that one equivalent of the yeWovi ferrocyanate is decomposed, 

 the free potash travels one way, and the hydroferrocyanic acid 

 the other. The oxygen unites with the hydrogen of the acid 

 and sets ferrocyanogen at liberty; this again unites with an 

 equivalent of the ferrocyanuret of potassium to form the^^rro- 

 sesquicyanuret" It is evident from this, that this gentleman 

 entertains a very different notion of the steps of the electro- 

 lysis to that which we feel justified in supporting, and that 

 therefore he has failed to place it in the point of view to which 

 we propose to adhere. 



(/.) We commenced our inquiry by carefully repeating Mr. 

 Smee's experiment in a diaphragm cell, charged throughout 

 with a strong solution of the yellow ferrocyanide of potassium. 

 A voltameter was included in the circuit, and the power of 

 twenty cells of the small constant battery was employed. Gas 

 was evolved at the platinode, which was tested and found to 

 be pure hydrogen ; it was in equivalent proportion to the gases 

 in the voltameter. No gas was at first evolved at the zincode, 

 but the solution in that cell became gradually red, particu- 

 larly at the surface. When 4 inches of hydrogen had been 

 collected at the platinode a slight disengagement of gas com- 

 menced at the zincode, which continued, and proved to be 

 oxygen, and was in the proportion of one-third of the gas from 

 the platinode. After sixteen cubic inches had been collected 

 from the platinode, we stopped the experiment and examined 

 the results. 



The platinode solution was much paler than before, and 

 was alkaline. The zincode solution was deep green and acid, 

 and the zincode plate was covered with a slight film of Prussian 

 blue. Crystals of the red ferrocyanide separated from the 

 zincode solution by spontaneous evaporation, and when the 

 evaporation was complete, a radiated mass of a purplish-brown 

 colour was obtained : on solution a small quantity of Prussian 

 blue remained, and the solution had lost its acid reagency. The 

 addition of acetate of lead to the solution produced but a 

 scanty precipitate, proving the quantity of yellow ferrocyanide 

 remaining in it to be but small. 



The explanation of these results is, we think, sufficiently 

 obvious. Ferrocyanogen was doubtless transferred to the 

 zincode, and potassium to the platinode, the former combined 

 with a portion of the ferrocyanide to form the subsesquiferro- 

 cyanide ; the process being accelerated by the abstraction of 

 a portion of the potassium passing over to the platinode, where 

 by its reaction upon the water ot" the solution it was converted 

 into potassa with the evolution of hydrogen. As the process 

 proceeded more ferrocyanogen was given off at the zincode 



