2 
PROFESSOR DANIELL AND DR. MILLER ON THE 
elements travel together under the influence of the voltaic current as compound 
anions and cations, or as iso-electric bodies ; that is, groups which are equivalent 
to each other, and to simple ions, in their relations to the electric forces. 
One of the most interesting results of this investigation, was the independent con- 
firmation which it afforded of two celebrated hypotheses, viz. that of Davy regarding 
the constitution of aqueo-acids, and the general analogy in the constitution of salts, 
whether derived from oxyacids or hydro-acids ; and that of Berzelius concerning 
the constitution of ammonium. 
It was with a view to extend our knowledge of such iso-electric groups, and to 
trace their connexion with chemical radicles, that we commenced our experiments. 
Before we enter upon their detail, it will be best to make a few remarks upon the 
mode of measuring their results, which has been adopted. It is founded upon the 
undoubted law of definite electric action ; and we have indifferently taken the amount 
of the ions disengaged at either or both the electrodes by the primary action of the 
current, or the secondary action of the elements. But there is another mode of 
effecting this purpose, by a diaphragm cell, in which the products of electrolysis may 
be kept separate ; a method founded upon the hypothesis, that the voltaic decomposi- 
tion of an electrolyte is not only effected by the disengagement of its anion and cation 
at their respective electrodes, but by the equivalent transfer of each to the electrodes ; 
so that the measure of the quantity of matter translated to either side of the dia- 
phragm might be taken as the measure of the electrolysis. 
This was the mode which was necessarily adopted in the investigation before ad- 
verted to, where attempts were made to compare the results of the electrolysis of 
aqueous solutions of acids # and alkalies'}- with the simultaneous decomposition of 
saline solutions. One circumstance, however, was then overlooked, which it is neces- 
sary to attend to in making the comparison, viz. that the disengagement of whole 
equivalents of the ions at the electrodes is only accompanied, upon the hypothesis 
assumed, by the actual transfer of half an equivalent to either side. This will clearly 
appear from the following diagram. 
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* First Letter, p. 108 . 
t Second Letter, p. 216. 
