8 
PROFESSOR DANIELL AND DR. MILLER ON THE 
equivalent in dry sulphuric acid, and that the sulphuric acid evolved at the zincode 
in the last experiment is the result of secondary action. Some sulphurous acid was 
evolved in the zincode cell, which doubtless arose from the action of the sulphuric 
acid upon the sulphite in contact with which it was produced. 
(k.) The experiment was varied by substituting hyposulphite of soda (NaO, S 2 0 2 ) 
for the sulphite, and with analogous results. Hydrogen was given off abundantly at 
the platinode, but no gas was evolved at the zincode. There was a strong odour of 
sulphurous acid at the latter, with a gradual deposition of sulphur. This doubtless 
arose from the secondary action of the sulphuric acid, which was first formed upon 
the salt with which it was in contact, by which hyposulphurous acid was disengaged, 
and immediately decomposed. The constitution of the hyposulphite being (NaO, 
S 2 0 2 ), that of the corresponding sub-oxysulphion would be S 2 0 3 , which if burnt at 
the zincode would produce S + S0 3 . 
5. We now proceeded to apply the method of electrolysis to solve a problem of the 
same nature as that of the three hydrates of the phosphoric acid, viz. to determine 
the exact relations of the yellow and red ferrocyanides of potassium. It is well known 
that two views have been taken of the constitution of these two salts : the first repre- 
sents the yellow salt as a ferrocyanide of potassium (K 2 , FeCy 3 ), and the red salt as a 
subsesquiferrocyanide of potassium K 3 + 2(Fe Cy 3 ). The second view represents the 
two salts as compounds of those metals with two distinct radicles, the former deno- 
minated ferrocyanogen (Fe Cy 3 ), the latter ferridcyanogen (Fe 2 Cy 6 ). The ferrocya- 
nogen forms a dibasic acid with hydrogen (H 2 , Fe Cy 3 ), the salts of which are pro- 
duced by the substitution of two equivalents of the metals for the two equivalents of 
hydrogen ; and the ferridcyanogen forms with hydrogen a tribasic acid (H 3 -J- Fe 2 Cy 6 ), 
with a similar substitution of three equivalents of the metals in their different salts. 
The real chemical difference, therefore, between the yellow and red ferrocyanides of 
potassium, consists in the latter containing half an equivalent less of potassium than 
the former ; and so with the other salts from the two classes the metallic elements 
are in the proportion of 1 to 1^. 
Now Mr. Porrett*, the discoverer of the hydroferrocyanic acid (or as he proposed 
to call it, the ferro-chyazic acid), long since determined that it travelled in the vol- 
taic circuit by the electrolysis of its salts, to the zincode, the iron accompanying the 
cyanogen in this transfer, contrary to what might previously have been expected. 
The question which we now proposed to determine was, whether ferridcyanogen as 
well as ferrocyanogen would thus constitute a distinct anion under the directing in- 
fluence of the battery. 
Mr. Smee~|~ has already determined that the subsesquiferrocyanide of potassium may 
be formed from the ferrocyanide by the action of the voltaic battery ; and has even 
proposed the process for obtaining the red salt upon a large scale. He, however, ex- 
plains the change by the action of nascent oxygen , which he supposes to be evolved 
* Philosophical Transactions, 1814, p. 529. f Philosophical Magazine, xvii. p. 196. 
