186 Prof. Daniell and Dr. Miller 07i the 



than could be absorbed by the yellow salt ; and it consequently 

 began to react upon the water, becoming converted by the 

 abstraction of its hydrogen into hydroferrocyanic acid, its 

 oxygen being evolved. The acid reaction is thus accounted 

 for, as well as the deposition of Prussian blue, from the well- 

 known spontaneous decomposition of the acid. 



{m.) This experiment was several times repeated with va- 

 riation of the quantities, but with substantially the same re- 

 sults. The evolution of oxygen from the zincode was hast- 

 ened by narrowing the dimensions of the electrode, which thus 

 presented a smaller surface for the reaction of the ferrocya- 

 nogen upon the ferrocyanide. When the process was con- 

 tinued for a long time, yellow crystals of the ferrocyanide 

 were formed in the platinode cell. Upon subsequent trial it 

 was found that a strong solution of potassa produced a similar 

 deposit, under ordinary circumstances, in a solution of the 

 yellow salt. It will probably be objected, that although the 

 red ferrocyanide is thus obviously formed by secondary action, 

 yet where once formed it may be capable of decomposition as 

 an electrolyte, in which ferridcyanogen acts as the anion. The 

 following experiment however is decisive against such a view. 



ill.) The diaphragm cell was charged throughout with a 

 strong solution of the red salt, the purity of which had been 

 tested. The solution was deep green by reflected light, but 

 red by transmitted light. The power of the same constant 

 battery was applied to it, and the platinode solution very 

 quickly changed its colour and became yellow. When 5*75 

 cubic inches of hydrogen had been collected from the plati- 

 node the yellow colour was perfectly pure ; the action was then 

 stopped. The liquid at the zincode was of a very dark brown- 

 green colour, and strongly acid, it had a pungent peculiar 

 smell, the liquid soon became perfectly opake, and one cubic 

 inch of oxygen was collected from the zincode. Though the 

 colour of the two solutions in the electrode cells had under- 

 gone such marked changes, the colour of that in the interme- 

 diate cell remained unaltered. The liquid from the platinode 

 cell yielded on evaporation tabular crystals of the yellow fer- 

 rocyanide, and when hydrate of potassa was added to the 

 zincode solution, a yellow colour was developed. 



Here then we obviously have the converse results of the last 

 experiments ; or the formation of ferrocyanide of potassium 

 from subsesquiferrocyanide by the abstraction of half an equi- 

 valent of ferrocyanogen transferred from the platinode to the 

 zincode. 



(o.) Could a doubt remain with regard to the conclusion to 

 be derived from these experiments, it must be removed by the 



