194 On Iodine. {Supr. 
a great number of metallic oxides, which really possess the proper- 
ties of acids. 
2, The acids-formed by hydrogen and another body. This set com- 
prehends hydro-chloric, hydriodic, and hydro-sulphuric acids. It 
is probable that in these acids chlorine, iodine, and sulphur, are 
the acidifying principles ; but as hydrogen enters into them all, I 
thought it better to deduce from it their general name. These 
different acids may be distinguished by the name hydracids. Among 
this set I conceive the numerous compounds of carbon and hydro- 
gen, which possess acid properties, ought to be arranged. The 
elements of some of these compounds, and perhaps of all of them, 
are in the same proportion in volume as in the preceding acids; and 
their molecules are doubtless arranged in an analogous manner. 
Among the vegetable acids there are several which draw their 
acid character from oxygen, because that body is the greatest con- 
stituent in them. This is the case with oxalic acid. But citric, 
saclactic, and acetic acids, probably owe their acid characters to the 
carbon, which they contain in the greatest proportion. We ought 
to admit this in particular in acetic acid, which we may conceive to 
be composed of equal parts by weight of carbon and water, or of 
three parts in volume of the vapour of carbon and two of the vapour 
of water.* I am likewise convinced that benzoic acid does not owe 
its acid properties to oxygen, but rather to the carbon and hydrogen. 
And I consider the classification of vegetable substances established 
by M. Thenard and myself (Rech. Physico-Chim. ii. 321,) as pre- 
senting exceptions. 
Prussic acid ought without doubt to be placed in a particular set, 
though near that of the hydracids; but it would be premature to 
determine its classification without knowing exactly its nature. 
Besides these different acids, chlorine, which was always reckoned 
among the acids, while considered as a compound of muriatie acid 
and oxygen, ought still to-be so, though a simple body. The same 
thing may be said of iodine, and of various other simple bodies, 
which have the property of combining with alkalies. Yet it appears 
to me more convenient to continue to class them among the simple 
bodies, and to reserve the term acid for the compound acids. But 
it becomes necessary to divide these bodies into as many sets as there 
are different generic characters. 
Though chlorine and iodine possess acidifying properties, and 
though they can form acids by combining with other bodies, we 
* This composition of acetic acid does not differ sensibly from that of woody 
matter, which does not possess amy acid characters. Here, then, are two bodies 
composed of carbon, oxygen, and hydrogen, in the same proportions, whose pro- 
perties are strikingly different. This isa cew proof that the arrangement of. the 
molecules in acompound has the greatest influence on the acid, alkaline, or neut al 
characters of the compound, Sugar, gum, and starch, lead to the same conclu- 
sions; for these substances, though composed of identic elements, and in the same 
proportion, have very different properties, 
