340 Mr Connewu on the Action of 
only done so after obtaining what appears to me to be experi- 
mental proof that the decomposition of the hydracids is a second- 
ary result. That hydrogen is evolved in such cases in definite 
quantity, there can be no doubt whatever. I have repeatedly 
found, on comparing dilute solutions of muriatic acid and of hy- 
driodic acid with dilute sulphuric acid in the volta-electrometer, 
that the quantity of hydrogen evolved was exactly the same from 
all these solutions. It is the question, whether, in the case of 
these hydracids, the hydrogen proceeds from the acid, or from 
the water, that affords room for difference of opinion. Mr Fa- 
RADAY contends, that it is derived from the acid, and that conse- 
quently the hydracids afford another instance of definite voltaic 
action. His reasons, which, at the utmost, are merely analogical, 
are, first, that chlorine and iodine combine with hydrogen atom 
to atom, as oxygen does; and, secondly, that chlorine can be di- 
rectly separated from lead, potassium, &c. in the dry state, by elec- 
tric agency. The first bemg an argument which can only be ad- 
dressed, in its full extent, to British chemists, can hardly be held 
to be of great weight ; and, with respect to the second, | think 
I shall soon make it at least doubtful whether one substance, 
namely, iodic acid, although it resists decomposition in solution, 
may not give way in the dry and fused state. But it is unneces- 
sary to dwell longer on mere argument from supposed analogy ; 
for I think I can bring forward a few experiments on the hydra- 
cids themselves, which appear to lead directly to the conclusion 
that the evolution of chlorine and iodine during voltaic action on 
solutions of those acids, is a secondary result, and that the hydro- 
gen is derived from water directly decomposed by the electric 
current. 
Into a tube of the capacity of one and a half dram, moderately 
strong muriatie acid was poured, and another tube of the same 
size was filled with distilled water. These two tubes were con- 
nected, as in Fig. 7, by asbestus moistened with distilled water ; 
the asbestus having been previously washed with diluted muriatic 
