440 _ Essay towards a natural 
this acid, which he calls in consequence hydro-carbonic acid, con- 
formably to the established nomenclature, is united with the 
oxides in such a proportion, that the volume of hydrogen which, 
it contains is double that of the oxygen of the oxide, so that 
when the latter is not very difficult to decompose, water is 
formed, and the carbonic acid gas remains alone combined with 
the metal, as happens with cyanogene, sulphur, chlore and iode, in 
the formation of the cyanures, sulphurets, chlorures and iodures. 
A third advantage equally important is, to prepare by the na- 
tural classification of simple bodies, that of compound substances, 
—a work of much more labour, and to which I purpose to devote 
another paper. I know that the compound bodies have been 
already classed in a manner much more conformable to their true 
analogies than their elements have been. Many things have 
doubtless been done in this respect ; but more perhaps remains 
to be done; and the discovery of the new substances with which 
the domains of chemistry have been enriched within these few’ 
years, cannot fail to lead to a modification and generalization of 
the principles according to which we now class compound sub- 
stances, and to determine in a more precise manner the signifi- 
cation of the names which serve to designate the various kinds 
of combinations, and particularly that of the words acid, alkali, 
salt, &e. 
I shall confine myself in this paper to the simple bodies, and 
shall divide them into three heads. JI shall offer in the first, 
some general considerations on the order according to which 
it is proper to arrange bodies, so that this order may be as con- 
formable as possible to their natural analogies; and on the 
means of avoiding the junction which has been hitherto made of 
the metals with bodies very different in almest all their other 
characters, and which have only been brought together because. 
the energy of their affinity for oxygen is nearly the same,—a cir-. 
cumstance certainly remarkable, but to which perhaps too much 
importance has been attached,—and which certain considerations 
on the natural order of simple bodies, the principal results of 
which I shall soon detail, ought to induce us to regard as se- 
condary, when it does not concur with other analogies which 
embrace the whole of the properties of the body. 
Under the second head, I shall unite under natural genera the 
bodies which present characters of resemblance so multiplied 
and important that it is impossible to separate them in every. 
classification which shall not be purely artificial; and | shall set- 
tle at the same time what places ought to be occupied in the 
natural order by the simple bodies which seem to form the pas- 
sage from one genus to another, presenting analogies very suing 
wit 
