ELECTROLYSIS OF SECONDARY COMPOUNDS. 
7 
In this case, as in that of the arseniate just described (3. /.), free oxygen was 
evolved, but the corresponding hydrogen arising from the secondary action of the 
potassium at the other electrode was taken up in the reduction of the arsenious acid in 
contact with which it was evolved. No such reduction of the arsenic acid was effected. 
It might have been anticipated that the oxygen in travelling with the arsenious 
acid to the zincode would have combined with it, and formed a portion of arsenic 
acid; but no such result took place: and it must be remarked, that two equivalents 
of oxygen instead of one would be required fully to oxidate the whole. We must, 
therefore, conclude that As 2 0 3 + O constitute what we may for the present distin- 
guish as a sub-oxarsenion. 
The experiment was repeated, by charging all the three cells of the apparatus with 
the solution of the salt, when oxygen was given off from the zincode as before, and 
arsenious acid was deposited in white crystals. 
( h .) The carbonates and oxalates may be compared together in the same point of 
view as acids of the same radicle in different states of oxygenation. It has been 
already stated that in the electrolysis of the former, carbonic acid and oxygen were 
found to be given off at the zincode in equivalent proportions to the alkali and 
hydrogen at the platinode ; proving those salts to be oxy-carbions of the respective 
metals*. When oxalate of ammonia was treated in the same way, carbonic acid 
alone was evolved at the zincode, and ammonia with hydrogen at the platinode*. 
Here the oxalion (or sub-oxycarbion) contains the elements of two equivalents of 
carbonic acid (C 2 0 3 -j- 0) = 2(C0 2 ). In numerous repetitions which we now made of 
these experiments, we found that although in the electrolysis of oxalate of ammonia 
(C 2 0 3 + O) was always exactly evolved, yet that it was not invariably in the form 
of carbonic acid, but in different proportions of oxalic acid with free oxygen and 
carbonic acid. It was thus proved that the burning of the oxalic acid into carbonic 
acid by its associated oxygen was a secondary process, and that the (C 2 0 3 -f O) 
which travelled in the circuit was in some way different from 2(C0 2 ). 
(i.) A similar comparison was then made between the sulphites and sulphates . 
In the electrolysis of the latter, it has been shown that sulphuric acid with an equi- 
valent of oxygen (which is evolved) travels to the zincode-f-. To determine the results 
of the former, all the cells of the diaphragm apparatus were charged with sulphite 
of potassa, and a voltameter was included in the circuit ; hydrogen was given off 
from the platinode in exact proportion to that from the voltameter ; but no oxygen 
was evolved from the zincode. 
The experiment was by itself ambiguous, for it did not determine whether (S0 2 -f O) 
travelled as S0 3 , or whether sulphuric acid was formed at the zincode by the secon- 
dary action of the oxygen upon the sulphurous acid. Judging from the analogy of 
the preceding instances, it is most probable that the oxygen with which the sulphurous 
acid is associated in the sub-oxysulphion is in a different state from that of the third 
* Second Letter, p. 222. + First Letter, pp. 107 et seq. 
