and combine to form relatively inactive salts. If they existed in
the free state, they would soon combine by reason of their strong
affinities. This is what in all ages of the world has taken
place, and this is why salts are common, acids and bases rare.
Active agents rarely exist in the free state in large quantities.
Oxygen seems to be an exception, but this is because there is a
superabundance of it. While vast quantities are locked up in
compounds in rocks, water, and salts of the earth, much remains
with which there is nothing to combine.

CHAPTER XVII.

CHLORHYDRIC ACID.

77. We have seen that salts are made by the union of acids and
bases. Can these last be obtained from salts?

78. Preparation of HCl.

Experiment 47.--Into a flask put 10 g. coarse NaCl, and add 20
cc. H2SO4. Connect with Woulff bottles [Woulff bottles may be
made by fitting to wide-mouthed bottles corks with three holes,
through which pass two delivery tubes, and a central safety tube
dipping into the liquid, as in Figures 22 and 23.] partly filled
with water, as in Figure 22. One bottle is enough to collect the
HCl; but in that case it is less pure, since some H2SO4 and other
impurities are carried over. Several may be connected, as in
Figure 23. The water in the first bottle must be nearly saturated
before much gas will pass into the second. Heat the mixture 15 or
20 minutes, not very strongly, to prevent too much foaming.