COSMOS, VOL. II - World eBook Library

DISCOVERIES IN THE CELESTIAL SPACES 729
toonth century, regarding the meteorological process. Van
Helm out was not acquainted with the simple method of taking
up and separating his gas sylvestre, (the name under which he
comprehended all un-inflammable gases, which do not maintain
combustion and respiration, and differ from pure atmospheric
air;) but he caused a light
to burn in a vessel under
water, and observed that when the flame was extinguished the
water entered, and the volume of air diminished. Van
Hclmont likewise endeavoured to show by determinations
of weight, (which we find already given by Cardanus), that
all the solid portions of plants are formed from water.
The alchemistic opinions of the middle ages regarding the
composition of metals, and the loss of their brilliancy by com-
led to a desire
bustion in the open air, (incineration, calcination)
of investigating the conditions by which this process was at-
tended, and the changes experienced by the calcined metals,
and by the air in contact with them. Cardanus, as early
as in 1553, had noticed the increase of weight that accompanies
the oxidation of lead, and perfectly in accordance
with the idea of the myth of Phlogiston, had attributed it to the
escape of a "celestial fiery matter," causing levity; and it was
not until eighty years afterwards that Jean Hey, a remarkably
skilful experimenter at Bergerac, who had investigated with
the greatest care the increase of weight during the calci-
nation of lead, tin, and antimony, arrived at the important
conclusion that this increase of weight must be ascribed to
the access of the air to the metallic
"
calx. Je responds et
soutiens glorieusemeiit," he says, "que ce surcroit de poids
vient de Fair qui dans levase a ete espessi."*
*
Eey, strictly speaking, only mentions the access of air to the oxides;
he did not know that the oxides themselves (which were then called the
earthy metals,) are only combinations of metals and air. According to
him, the air makes "the metallic calx heavier, as sand increases in weight
when water hangs about it." The calx is susceptible of being saturated'
with air. " L'air espaissi s'attache & la chaux, ainsi le poids augmente du
commencement jusqu'a la fin: mais quand tout en est aflfuble, elle n'eu
scauroit prendre d'avantage. Ne continuez plus votre calcination soubs
cet espoir, vous perdriez vostre peine." Key's work thus contains the
first approach to the better explanation of a phenomenon, whose more
complete understanding subsequently exercised a favourable influence in
reforming the whole of chemistry. See Kopp, Gesch. der Chemie, Th. iii.