1815.] On Iodine. 195 
ought not at present, considering the small number of acids which 
they form, and whose existence even is not sufficiently established, to 
be in a hurry to form these acids into particular sets. We ought to 
be so the less because there are bodies, as carbon, which are acidi- 
fied by oxygen, and which in their turn acidify other bodies. Be- 
sides these considerations which I have offered on acidity, showing 
that it is not proportional in an acidified body to the quantity of the 
acidifying principle, and that it is greatly modified by the arrange- 
ment of the molecules, it is necessary to wait till experiment has 
furnished us with more light before pronouncing on its true cha- 
racters, and on the circumstances which produce it. We know, 
indeed, that acids and acidifying bodies have an electric energy 
which is negative with respect to that of the alkalies and the alkali- 
fying bodies. But this is not sufficient; and we are still far from 
being able to assign from the electric energics of compounds, if the 
character of their compound ought to be neutral, acid, or alkaline. 
Thus silver having a very weak affinity for oxygen, it would seem 
that it ought to approach it by the nature of its electric energy ; and 
yet the oxide of silver, in which I have found a small degree of 
solubility, is very alkaline, for it completely neutralizes the acids ; 
and azote, which appears to approach oxygen, chlorine, and iodine, 
forms a very weak compound with hydrogen, though this last pos- 
sesses a very great positive electric energy. We have more and 
more reason, then, to admit that the neutral, acid, or alkaline, 
character of a compound does not depend entirely upon the cha- 
racters of its constituents, but likewise upon their proportions in 
volume, and their condensation; or, in other words, upon the 
arrangement of their molecules. 
ADDITIONS, 
Lhave said, vol. v.p. 106, that on passing water and iodine in vapour 
through a porcelain tube at a red heat, no oxygen was disengaged, 
and consequently that the water was not decomposed by the iodine. 
The same experiment repeated afterwards a second time gave me 
the same result, that is to say, that I obtained no oxygen. Never- 
theless, the consequence which I drew from it is not exact, as I shall 
now show. M. Ampere having exposed during several months a 
solution of iodine in water to the action of solar light, observed that 
it was entirely freed from colour, and requested me to examine what 
could be the cause of this phenomenon. We ascertained that the 
water contained a mixture of iodie acid and hydriodic acid in very 
small proportions ; and on letting fall into it some drops of sulphuric 
acid or solution of chlorine, the water assumed an orange-brown 
tolour, and gave out the peculiar odour of jodine. Sulphurous acid 
did not colour it ; but hydro-sulphurie acid rendered it milky, on 
account of the sulphur which precipitated. ‘These experiments de 
monstrate evidently the presence of hydriodic and iodic acids in the 
solution of iodine under examination ; and we imitated it by mixing 
together very dilute solutions of these two acids. The only conse- 
N 2 
