196 On Iodine. {Serr. 
quence which we can deduce from this fact is, that water was de- 
composed. Its oxygen formed with iodine iodic acid, and its 
hydrogen hydriodic acid. But the quantity of the two acids which 
can exist together in solution in water is subordinate to this condi- 
tion, that when they are concentrated to a certain degree they de- 
compose one another. 
As we can in general substitute a certain elevation of tempera- 
ture for solar light, I made a mixture of vapour of iodine and 
water pass again through a red-hot porcelain tube, and I attentively 
examined the products. No gas passed; and the water condensed 
had the same intensity of colour with cold water saturated with 
iodine. I heated it, in order to deprive it of its colour, and I suc- 
ceeded. ‘This water, which had no smell, and no action on litmus 
any more than the water obtained by M. Ampere, had likewise all 
the characters of it, and I easily recognized in it the presence of 
iodic and hydriodic acids. As before being discoloured by heat it 
had exactly the appearance of a cold solution of iodine, I thought 
that both might be similar. To verify this suspicion, I slightly 
heated a cold solution of iodine, in order to deprive it of its colour, 
an effect which may equally be produced by exposing it to the air. 
It then presented exactly the same characters as a solution of iodine 
which had been made colourless by long exposure to light, and as 
that which I had obtained by passing water and iodine through a 
red-hot tube, and rendered colourless by boiling. None of these 
solutions was coloured by sulphurous acid ; but all of them were 
coloured by chlorine. ‘This is because, on the one hand, the 
hydriodic and iodic acids exist in them in very small quantity ; and 
because on the other there is five times as much iodine in the first 
acid as in the second. I have, however, succeeded in rendering the 
solution of the two acids coloured by sulphurous acid, by first satu- 
rating with ammonia, and then concentrating by evaporation. 
It follows from these observations that when iodine is in contact 
with water it decomposes this liquid, and produces with its elements 
iodic and hydriodic acids. ‘This action of iodine on water appears 
to me entirely independent of the solar light: and when a solution 
of iodine is deprived of its colour by exposure to light for some 
months, as in the experiment of M. Aimpere, I ascribe the effect to 
the gradual evaporation of the iodine. It appears to me probable 
that iodine is dissolved in water only by the action of the hydriodic 
acid, which is formed at the same time that the solution takes place. 
But I have already remarked that we do not succeed in depriving 
hydriodie acid holding iodine in solution of its colour by boiling, 
while we easily do so to water which has been in contact with this 
substance. J presume that in this last case the hydriodic acid exer- 
cising some part of its action on the jodie acid, retains the iodine 
with less energy, and of course lets it be disengaged with more 
facility. 
I have ascertained that on exposing to light a solution of chlorine 
‘in water, chloric acid is produced. 
