"
We follow here the grouping according to external forms, and the student
should compare it with the groups marked in the lemniscate arrangement
shown in Article II (p. 377, properly p. 437, February), reading the group
by the disks that fall below each other; thus the first group is H, Cl, Br,
I (hydrogen, chlorine, bromine, iodine) and a blank for an undiscovered
element. The elements grow denser in descending order; thus hydrogen is an
invisible gas; chlorine a denser gas visible by its colour; bromine is a
liquid; iodine is a solid--all, of course, when temperature and pressure
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.
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