are normal. By the lowering of temperature and the increase of pressure, an
element which is normally gaseous becomes a liquid, and then a solid.
Solid, liquid, gaseous, are three interchangeable states of matter, and an
element does not alter its constitution by changing its state. So far as a
chemical "atom" is concerned, it matters not whether it be drawn for
investigation from a solid, a liquid, or a gas; but the internal
arrangements of the "atoms" become much more complicated as they become
denser and denser, as is seen by the complex arrangements necessitated by
the presence of the 3546 ultimate atoms contained in the chemical "atom" of
gold, as compared with the simple arrangement of the 18 ultimate atoms of
hydrogen.

According to the lemniscate arrangement, we should commence with hydrogen
as the head of the first negative group, but as it differs wholly from
those placed with it, it is better to take it by itself. Hydrogen is the
lightest of the known elements, and is therefore taken as 1 in ordinary
chemistry, and all atomic weights are multiples of this. We take it as 18,
because it contains eighteen ultimate atoms, the smallest number we have
found in a chemical element. So our "number-weights" are obtained by
dividing the total number of atoms in an element by 18 (see p. 349,
January).

[Illustration: PLATE V.]

HYDROGEN (Plate V, 1).--Hydrogen not only stands apart from its reputed
group by not having the characteristic dumb-bell shape, well shown in
sodium (Plate I, opposite p. 349, January), but it also stands apart in
being positive, serving as a base, not as a chlorous, or acid, radical,
thus "playing the part of a metal," as in hydrogen chloride (hydrochloric
acid), hydrogen sulphate (sulphuric acid), etc.