which we call Heat. 119 
atoms, is already active in simple substances, and that in these 
likewise two or more atoms are combined to form one molecule. 
For instance, let equal volumes of oxygen and nitrogen be 
given. A mixture of these gases contains a certain number of 
molecules, which consist either of two atoms of oxygen or of two 
atoms of nitrogen. Conceive the mixture to pass into a chemical 
compound, and the latter then contains just as many molecules, 
which are merely constituted in a different manner, masmuch as 
each consists of an atom of oxygen and an atom of nitrogen. 
Hence there is no reason why a change of volume should take 
place. If, on the other hand, one volume of oxygen and two of 
nitrogen are given, then in the mixture each molecule consists 
of two, and in the compound of three atoms. The chemical 
combination, therefore, has caused the number of molecules to 
diminish in the ratio of 3: 2, and consequently the volume ought 
to diminish in the same ratio. . 
It is well known that some simple substances do not, in the 
gaseous form, occupy the volume which their atomic weights 
and the volumes of their combinations would lead us to antici- 
pate, but another, and in most cases a smaller volume, which 
bears to the former a simple ratio. A special investigation of 
these substances would here be out of place, more especially as 
two of them, sulphur and phosphorus, deport themselves in other 
respects in so remarkable a manner, in consequence of the variety 
of conditions they are capable of assuming, that we may reason- 
ably expect further discoveries from chemistry with respect to 
these bodies; and then, perhaps, besides other irregularities, 
those of the volumes of their vapours will be explained. Never- 
theless I may here recall one circumstance which in some cases 
may possibly facilitate this explanation. I refer to the fact, that 
the above hypothesis, according to which the molecules of simple 
substances each consist of ¢wo atoms, may not be the only pos- 
sible one. 
On comparing with each other all cases of simple and com- 
pound gases, we must not expect to find immediately a perfect 
agreement throughout. I am of opinion, however, that, under 
the present uncertainty with respect to the inner constitution of 
several bodies, and particularly of those which possess a compli- 
cated chemical composition, too great weight ought not to be 
laid upon individual anomalies; and I deem it probable, that, 
by means of the above hypothesis respecting the molecules of | 
simple substances, all relations of volume in gases may be referred 
back to the theorem, that the several molecules of all gases possess 
equal vis viva in reference to their translatory motion. 
14, Proceeding to treat the subject mathematically, we will 
