3 1868. ] The Past and Present of Chemistry. 29 
probability that the number of oxygen atoms in a molecule of ozone 
stands to the number in a molecule of ordinary oxygen in the pro- 
portion of three to two. ‘Thus, ozone and ordinary oxygen consist 
of molecules, the composition of which differs, not in respect of the 
quality but of the number of atoms which they contain. Imagine 
the oxygen atoms as so many soldiers belonging to one army, 
although this comparison be a rough one, it is not so inappropriate 
as might be imagined; for in fact, in chemical action, these atoms 
do fight against the alliance between other kinds of atoms, and 
must vanquish their opposition before they can take up and main- 
tain new positions. A certain weight of oxygen consists of an 
unspecified number of these atoms or soldiers ; but in equal weights 
of ordinary and of ozonized oxygen, the same number is arranged 
in a different manner. A given weight of common oxygen contains 
a certain number of these atoms or warriors, which are marshalled 
in a certain number of battalions or molecules ; an equal weight of 
ozone contains the same number of exactly similar atoms or warriors, 
which are, however, placed in a smaller number of molecules or bat- 
talions. A molecule of ozone is numerically a stronger battalion than 
a molecule of oxygen. By the help of this crude simile, it is easy to 
understand how the same element can pass from one of these con- 
ditions into the other, and how, according to the different mar- 
shalling of the said atoms, the same element may have different 
chemical effects upon other bodies—may attack the molecules or 
battalions of which they consist in a different manner. 
The explanation just offered of the possibility of similar atoms 
being arranged in different kinds of molecules, is manifestly ap- 
plicable also to dissimilar atoms. Imagine different kinds of ele- 
mentary atoms—carbon, hydrogen, oxygen atoms for instance, to 
be represented by different kinds of soldiers, as infantry, cavalry, 
riflemen. Equal weights of acetic acid and sugar contain the 
same quantities of carbon, hydrogen, and oxygen, i.e. the same 
number of atoms of the three elements, or of warriors of the three 
different arms. But the arrangement of these warriors in military 
order—in battalions or regiments—is dissimilar in the two bodies. 
A molecule of sugar contains a greater number (at least thrice, 
perhaps six times as great) of atoms of carbon, hydrogen, and 
oxygen as a molecule of acetic acid. ~Although the composition of 
acetic acid is identical with that of sugar, both as regards quantity 
and quality of the contained elements, yet the molecules of the two 
substances are of dissimilar formation, z.e. they contain the same 
elementary atoms in different numbers though in the same propor- 
tions, and we know with still greater certainty that in aldehyde, only 
half as many atoms of carbon, hydrogen, and oxygen are united to 
form a molecule, as in acetic ether or butyric acid, which in all other 
respects have exactly the same composition, containing the same 
elements in the same proportions. 
