444 Essay towards a natural 
iode and chlore a permanent acid gas with hydrogen : the hydro~ 
sulphates present the greatest analogy with the hydro-iodates 
and hydro-chlorates: they are reduced into sulphurets, as the — 
latter are into iodures and chlorures, when they are insoluble, or 
after havitig evaporated their solutions, and dried their residues— 
properties which still more closely approximate iode and chlore 
to sulphur than to oxygen. It is impossible to separate iode 
from chlore, from which it differs only because the same cha- 
racters are manifested at a less degree of energy; and _never- 
theless, why should iode be a supporter of combustion rather 
than sulphur, which is united to most of the metals with a greater 
extrication of light and heat? Shall we say that the sulphur is 
combined with the oxygen of the atmospheric air when we ex- 
pose it to a sufficient temperature, and that this is not the case 
with iode also? But is the latter not also combined with oxy- 
gen when we place it in contact with the gaseous oxide of chlore, 
discovered by the celebrated cheinist who was the first to de- 
compose the alkalis, and demonstrate that chlore is a simple 
body, conformably to the opinion already given by the French 
chemists as an admissible hypothesis? It is of no use to insist 
longer on considerations of this kind: what precedes is sufficient 
to show how easy it is to be led into error, and to give too much 
importance to certain analogies, when we commence by esta- 
blishing between the bodies which we purpose to classify, genera] 
divisions founded on a single character only. We should then 
deceive ourselves still more, if we thought to be able to arrange 
the simple bodies in an order conformable to their natural ana- 
logies, by forming of them a series dependent on their various 
degrees of affinity for one of them, for oxygen for instance. On 
comparing all the properties which those substances present, we 
find that they form asystem in which every body belongs, on one 
side or the other, to bodies adjoining them, by analogies so ‘ 
strong that we are not able to establish in any way the complete 
separation which will be required by the reduction of the system 
into a single series; so that we must represent it to ourselves as 
a sort of circle, in which two bodies placed at the two extremities 
of the chain formed by all the rest, approach and unite mutually 
by common characters. I have long endeavoured to establish a 
natural order among simple bodies, by arranging them in a sin- 
gle series, which should commence with those whose properties 
presented the most complete opposition to those of the bodies 
which I attempted to place at the end of the series: these at- 
tempts have not been attended with any success; and it is by 
them that I have been led to adopt an order quite different, of 
which I shall in the first place attempt to give a general idea, 
‘ which 
