72 WATER AND SOLUTION
that the lump soon grows very hot, giving off clouds of steam,
and swells up and tumbles apart to form a fluffy white powder.
Stir a little of this powder with water. It makes a milky
suspension. If some of this suspension is placed in a test tube
the white solid settles and a clear liquid remains above. This
liquid colors litmus blue.
It is obvious from the large amount of heat developed that
the affinity between calcium oxide and hydrogen oxide is very
great.
CaO + H 2 O->Ca(OH) 2
The same substance, calcium hydroxide, is formed here as in the
action of calcium metal on water, only in this case no hydrogen is
displaced. Calcium hydroxide is not very soluble in water, and
mainly on that account it is not as strong a base as sodium hydrox-
ide. The saturated solution is called "lime water."
- Magnesium Oxide and Water. Burn a piece of mag-
nesium ribbon held in pincers so that the ash falls into a
clean dish. Stir half of the ash into a small beaker full of
water and test the solution with litmus. Wet the other half
of the ash with a single drop of water and place the moistened
mass on one side of a strip of red litmus paper. Look on the
other side of the paper and note that in a little while the center
of the wet spot turns blue.
MgO + H 2 O -» Mg(OH) 2
Magnesium oxide does not combine as energetically with water
as calcium oxide, and the magnesium hydroxide formed is very
much more insoluble than calcium hydroxide. Thus the satu-
rated solution of the hydroxide is barely alkaline enough to color
litmus blue.
The hydroxides of aluminum and of the heavy metals are much
more insoluble even than magnesium hydroxide, and for the most
part their suspensions do not affect litmus. The hydroxides of the
metals are, however, considered basic although very weakly so. - Non-Metal Oxides and Water. Burn small pieces
of (a) phosphorus (use red phosphorus), (6) sulphur, and
(c) carbon (charcoal) successively in large, clean bottles of
air. The phosphorus and sulphur may be introduced in a