ON ELECTROLYSIS. 739 
of the double decomposition which has gone on. Moreover, there are 
‘the apparent alternatives, just as in the last table. To get rid of alter- 
natives, decide that the liberated ions are single, one anion A,, and one 
-eation C,, where & and 1 may be equal as a special case. Then the por- 
tion of the table referring to loss of compounds is :— 
Original substance —_ a Lost in anode vessel Total loss 
A,@C—C,) | ay —a, 0 
A,(2C —C,) Oy —a, 0 
A,(3C-C,) a, 1—a, 1 
A (2C-C,) a, —a, 0 
C,(2A—A,) Woy. ap 1 
If no double decomposition had gone on, the substances would have 
simply been A,C,, A.C., &ec. The meaning of A,(2C — C,) is: all the 
<ompounds into which A, happens to enter, with the express exclusion of 
A,C,, this being considered separately, along with A,C,, A;C,, .. ., &., 
in the last line of the table. 
The remainder of the table, dealing with the secondary or bye-products 
formed, is too indeterminate to be instructive ; for even if double decom- 
position had been excluded originally, it must be supposed to occur now, 
and the substances formed can only be written :— 
Substance formed in cathode A t Substance formed in anode A t 
vessel es || vessel oe 
A,(@C-—C, —C;) CEH | C\(2A—A,—A,) CO ae 61 
A,(2C —C,—C,) Aa + Yo | C,2A—A,—A,) Go + Yo 
A(2C—C,) i—(a 7) C,(@A—A, 1—(a,+¥;,) 
A, (2C a Chy a, + Yn C(ZA —A, rs A.) bane 
, 
where A,(3C —C, — C3) stands for A,C, + A,C,+A,C;+..., or 
any of them—+.e. for all the possible new combinations of A, with 
cations; the C, being excluded because A,C, is certainly not a new 
compound; and C, being excluded because, being the cation deposited on the 
electrode, there is bound to be a deficiency of it rather than an excess, 
unless indeed more is brought over by migration than is deposited. 
Cases of even this anomaly were discovered by Hittorf among the 
iodides and chlorides of zinc and cadmium, especially when dissolved 
in alcohol; more than one equivalent of iodine is carried over towards 
anode, as much indeed, in one case, as two equivalents. This, however, 
is regarded as exceptional by everybody, and is usually explained by 
supposing a sub-salt to travel bodily with the simple ion thus: 
3CdI, = Cd + (2CdI + 21,), where the quantity in brackets may be 
the true anion. The same idea has been extended to other and more 
ordinary cases. 
