10 
PROFESSOR DANIELL AND DR. MILLER ON THE 
was hastened by narrowing the dimensions of the electrode, which thus presented a 
smaller surface for the reaction of the ferrocyanogen upon the ferrocyanide. When 
the process was continued for a long time, yellow crystals of the ferrocyanide were 
formed in the platinode cell. Upon subsequent trial it was found that a strong solu- 
tion of potassa produced a similar deposit, under ordinary circumstances, in a solu- 
tion of the yellow salt. It will probably be objected, that although the red ferro- 
cyanide 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. 
(■ n .) 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 m 75 cubic inches of hydrogen had been collected from the platinode 
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 elec- 
trode cells had undergone such marked changes, the colour of that in the interme- 
diate cell remained unaltered. The liquid from the platinode cell yielded on evapo- 
ration tabular crystals of the yellow ferrocyanide, 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 equivalent 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 results of the following arrangement. The 
zincode cell was filled with a dilute solution of potassa, and the connecting cell with 
the same. The platinode cell was charged with a strong solution of the red ferro- 
cyanide. This solution previously to the commencement of the experiment gave no 
blue solution with perchloride of iron. The liquid in the zincode and connecting 
cells speedily became yellow, and after a short time the solution in the platinode cell 
also became yellow. All the solutions were now found to contain the yellow ferro- 
cyanide. Thus it was quite clear that no such compound as ferridcyanogen travelled 
from the red salt when exposed to electrolysis, but that the red salt was converted 
into the yellow by the abstraction of ferrocyanogen from the platinode, which ferro- 
cyanogen being transferred to the zincode, there formed with the potassium presented 
to it by electrolysis the same yellow ferrocyanide. 
In order to extend further our knowledge of the electrolysis of this class of secon- 
dary compounds, the following experiments were made : — 
(p.) A diaphragm apparatus was charged with a strong solution of cyanide of po- 
