A Theory of the 
[November, 
644 
their peroxides are unsaleable. When the element is of 
feeble polarity the oxygen determines a slight preponderance 
of negative properties in the compound, as in the case of 
silicic oxide. When combined with negative elements the 
negative character of the oxygen is superadded to the nega- 
tivity of the negative elements. At the same time the sta- 
bility of the union decreases as the negativity of the element 
becomes more pronounced. The oxides of sulphur are 
formed by direCt synthesis, and are comparatively stable ; 
the oxides of chlorine are not formed by direCt union of the 
elements, and are decomposed under conditions of slight 
disturbance. This indicates that the atoms of oxgen in the 
oxides of chlorine are linked to each other, — evidently a 
condition of unstable union. The salts formed from these 
anhydrides are more stable, because the positive element 
reinforces the feeble polarity of the chain. If we examine 
the chlorides of the elements we find less evidence of high 
atomicity in negative atoms ; and if we consider those cases 
where union takes place between mutually attradting ele- 
ments of opposite character, and produces neutral, stable, 
substances as the result, we find, on the contrary, that not 
only do the most negative elements possess low atomicity, 
but that the progression towards this condition is regular in 
each cycle. Thus the metal sodium combines with one atom 
of chlorine, and the metal magnesium with two atoms. The 
earth metal aluminium combines with three atoms of 
chlorine, and silicon with four atoms of chlorine or of hy- 
drogen. Phosphorus combines with three atoms of hydro- 
gen, and with three positive atoms by means of intermediate 
oxygen atoms in the orthophosphates. Sulphur combines 
with two positive atoms in sodium sulphide, and indiredtly 
with two atoms of sodium in sodium sulphate ; and chlorine 
combines with one positive atom in sodium chloride. And 
if we confine the conception of atomicity to cases of union 
of elements resulting in the evolution of heat, in stability 
of the molecule, and neutrality, caused by satisfied affinity, 
we find it everywhere to be highest in the middle cf the 
cycle. In the middle of the cycle, also, we find the mini- 
mum of atomic volume, and the occurrence of the properties 
which seem to depend upon proximity of atoms, viz., high 
melting-point, rigidity, and minimum expansion by heat, 
and that these properties of matter always occur simulta- 
neously with high atomicity is evidence of the existence of 
a common cause of the phenomena. 
The attraction between atoms, which brings about che- 
mical union and the formation of the molecules of compounds, 
