118 Prof. Clausius on the Nature of the Motion 
vis viva of the several molecules arising from their translatory 
motion, the only one which Krénig considers. 
If we apply this to simple gases, and assume that, when pres- 
sure and temperature are the same, equal volumes contain the 
same number of atoms—a hypothesis which for other reasons is 
very probable,—it follows that, in reference to their translatory 
motion, the atoms of different gases must have the same vis viva. 
We will next examine in what manner this theorem remains 
true when applied to the molecules of compound gases. 
12. In the first place, let us compare compound gases amongst 
themselves, e. g. two gases to form which the constituents have 
combined in ratios of volume respectively equal to 1:1 and 1:2. 
Nitric acid and nitrous acid may serve as examples. 
With respect to these two gases, we know that quantities con- 
taining the same amount of oxygen occupy the same volume. 
Hence here, too, equal volumes contain the same number of mo- 
lecules, although in the one gas each molecule consists of two, 
and in the other of three atoms; and we must further conclude, 
that even these differently constituted molecules have the same 
vis viva with respect to their translatory motion. 
In most other compound gases we are led to the same conclu- 
sion ; and in cases which do not submit themselves to this rule, 
it does not appear to me impossible that the discrepancy may be 
accounted for in one or both of two ways: either the gas was not 
sufficiently removed from its points of condensation when its vo- 
lume was determined, or the chemical formula hitherto employed 
does not properly represent the manner in which the atoms are 
combined to form molecules. 
On comparing compound and simple gases, however, an un- 
mistakeable deviation from the foregoing rule shows itself, 
inasmuch as the space corresponding to an atom of the simple 
gas does not correspond to a molecule of the compound one. 
When two simple gases combine in equal volumes, it is well 
known that no change of volume takes place, whilst according 
to the above rule the volume ought to be diminished in the ratio 
of 2:1. Again, when a volume of one gas combines with two or 
three volumes of another, the combination is found to occupy 
two volumes, whereas according to rule it ought only to occupy 
one volume, and so on. 
13. On seeking to explain these curious anomalies, and espe- 
cially to find a common law governing the relations of volume 
in gases, I was led to adopt the following view as being most 
plausible. I beg to offer the same to the scientific public as a 
hypothesis which is at least worthy of further examination. 
I assume that the force which determines chemical combi- 
nation, and which probably consists in a kind of polarity of the 
