familiar class of solutions, since in the laboratory
substances are much more frequently used in the form of solutions than
in the solid state.

~Circumstances affecting the solubility of a solid.~ The solubility of a
solid in a liquid depends upon several factors.

1. _Nature of the solid._ Other conditions being the same, solids vary
greatly in their solubility in liquids. This is illustrated in the
following table:

_Table of Solubility of Solids at 18 deg._

100 cc. of water will dissolve:

Calcium chloride 71.0 g.
Sodium chloride 35.9
Potassium nitrate 29.1
Copper sulphate 21.4
Calcium sulphate 0.207

No solids are absolutely insoluble, but the amount dissolved may be so
small as to be of no significance for most purposes. Thus barium
sulphate, one of the most insoluble of common substances, dissolves in
water to the extent of 1 part in 400,000.

2. _Nature of the solvent._ Liquids vary much in their power to dissolve
solids. Some are said to be good solvents, since they dissolve a great
variety of substances and considerable quantities of them. Others have
small solvent power, dissolving few substances, and those to a slight
extent only. Broadly speaking, water is the most general solvent, and
alcohol is perhaps second in solvent power.

3. _Temperature._ The weight of a solid which a given liquid can
dissolve varies with the temperature. Usually it increases rapidly as
the temperature rises, so that the boiling liquid dissolves several
times the weight which the cold liquid will dissolve. In some instances,
as in the case of common salt dissolved in water, the temperature has
little influence upon the solubility, and a few solids are more soluble
in cold water than in hot. The following examples will serve as
illustrations:

_Table of Solubility at 0 deg. and at 100 deg._

100 cc. of water will dissolve:

At 0 deg. At 100 deg.

Calcium chloride 49.6 g. 155.0 g.
Sodium chloride 35.7 39.8
Potassium nitrate 13.3 247.0
Copper sulphate 15.5 73.5
Calcium sulphate 0.205 0.217
Calcium hydroxide 0.173 0.079

~Saturated solutions.~ A liquid will not dissolve an unlimited quantity of
a solid. On adding the solid to the liquid in small portions at a time,