dryness; what weight of solid was left?

7. Account for the fact that sugar sometimes deposits from molasses,
even when no evaporation has taken place.

8. (a) From the standpoint of the theory of electrolytic dissociation,
write the simple equation for a dilute solution of copper sulphate
(CuSO_{4}); this solution is blue. (b) In the same manner, write one
for sodium sulphate; this solution is colorless. (c) How would you
account for the color of the copper sulphate solution?

9. (a) As in the preceding exercise, write a simple equation for a
dilute solution of copper chloride (CuCl_{2}); this solution is blue.
(b) In the same manner, write one for sodium chloride; this solution
is colorless. To what is the blue color due?

10. What component is present in concentrated sulphuric acid that is
almost wanting in very dilute sulphuric acid?

11. Why will vegetables cook faster when boiled in strong salt water
than when boiled in pure water?

12. How do you explain the foaming of soda water?

CHAPTER X

ACIDS, BASES, AND SALTS; NEUTRALIZATION

~Acids, bases, and salts.~ The three classes of compounds known
respectively as acids, bases, and salts include the great majority of
the compounds with which we shall have to deal. It is important,
therefore, for us to consider each of these classes in a systematic way.
The individual members belonging to each class will be discussed in
detail in the appropriate places, but a few representatives of each
class will be described in this chapter with special reference to the
common properties in accordance with which they are classified.

~The familiar acids.~ _Hydrochloric acid_ is a gas composed of hydrogen and
chlorine, and has the formula HCl. The substance is very soluble in
water, and it is this solution which is usually called hydrochloric
acid. _Nitric acid_ is a liquid composed of hydrogen, nitrogen, and
oxygen, having the formula HNO_{3}. As sold commercially it is mixed
with about 32% of water. _Sulphuric acid_, whose composition is
represented by the formula H_{2}SO_{4}, is an oily liquid nearly twice
as heavy as water, and is commonly called _oil of vitriol_.

~Characteristics of acids.~ (1) All acids contain hydrogen. (2) When
dissolved in water the molecules of the acid dissociate into two kinds
of ions. One of these is always hydrogen and is the cation (+), while
the other consists of the remainder of the molecule and is the anion
(-). (3) The soluti