strongly to the word "atomicity;" he could not conceive of one atom
being more atomic than another; he could understand the atomicity of
a molecule or the equivalency of an atom, but not the atomicity of an
atom; the expression seemed to him complete nonsense. He next considered
the possibility of assigning a fixed limit to this valency or adicity of
an atom, and concluded that the adicity was not absolutely fixed, but
was fixed in relation to certain elements, e.g., C never combines with
more than four atoms of H; O never more than two atoms of H, etc. The
adicity of an element when combined with two or more elements is usually
higher than when combined with only one, e.g., NH_{3}, NH_{4}Cl. The
term "capacity of saturation," may be used as a synonym for adicity, if
care be taken to distinguish it from other kinds of saturation, such as
an acid with an alkali, etc. Adicity is, however, quite distinct from
combining force; the latter is indicated by the amount of heat evolved
in the combination.

The lecturer then proceeded to criticise a statement commonly found
in text books, that chemical combination suppresses altogether the
properties of the combining bodies. The reverse of this statement is
probably true. To take the case commonly given of the combination of
copper and sulphur when heated; this is good as far as it goes, but
there are numerous instances, as ClI, SSe, etc., where the original
properties and characters of the combining elements do not completely
disappear. The real statement is that the original properties of the
elements disappear more or less, and least when the combination is weak
and attended with the evolution of a slight amount of heat, and in every
case some properties are left which can be recognized. So with reference
to the question of atomic and molecular combination, as atomic
combination does not necessarily produce change, it does not differ in
this respect from what is usually called molecular combination.