cc. chlorhydric acid, HCl. Adjust as for O (Fig. 7), except that
no heat is to be applied. If the action is not brisk enough, add
more HCl. Collect several receivers of the gas over water, adding
small quantities of HCl when necessary. Observe the black
floating residuum; it is carbon, lead, etc. With a glass plate
remove the receivers, keeping them inverted (Fig. 11), or the H
will escape.

32. The Chemical Change is as follows:--

Zinc + hydrogen chloride = zinc chloride + hydrogen.

Zn + 2 HCl = ZnCl2 + 2H.

Complete by adding the weights, and explain. Notice that the
water does not take part in the change; it is added to dissolve
the ZnCl2 formed, and thus keep it from coating the Zn and
preventing further action of the acid. Note also that Zn has
simply changed places with H, one atom of the former having
driven off two atoms of the latter. The H, having nothing to
unite with, is set free as a gas, and collected over water. Of
course Zn must have a stronger chemical affinity for Cl than H
has, or the change could not have taken place. Why one Zn atom
replaces two H atoms will be explained later, asfar as an
explanation is possible. This equation, should be studied
carefully, as a type of all equations. The left-hand member shows
what were taken, i.e. the factors; the right-hand shows what were
obtained, i.e. the products. H2SO4 might have been used instead
of HCl. In that case the reaction, or equation, would have been:
--