Experiment 61.--Dissolve 3 g. sodium carbonate, Na2CO3, in 10 or
15 cc. H2O in an e.d., and bring it to the boiling-point. Then
add to this a mixture of 1 or 2 g. calcium hydrate, Ca(OH)2, in 5
or 10cc. H2O. It will not dissolve. Boil the whole for five
minutes. Then pour off the liquid which holds NaOH in solution.
Evaporate if desired. This is the usual mode of preparing NaOH.

The reaction is Na2CO3 + Ca(OH)2 = 2NaOH + CaCO3. The residue is
Ca(OH)2 and CaCO3; the solution contains NaOH, which can be
solidified by evaporating the water. Sodium hydrate is an
ingredient in the manufacture of hard soap, and for this use
thousands of tons are made annually, mostly in Europe. It is an
important laboratory reagent, its use being similar to that of
ammonium hydrate. Exposed to the air, it takes up water and CO2,
forming a mixture of NaOH and Na2CO3. It is one of the strongest
alkalies, and corrodes the skin.

Experiment 62.--Put 20 cc. of H2O in a receiver. With the forceps
take a piece of Na, not larger than half a pea, from the naphtha
in which it is kept, drop it into the H2O, and at once cover the
receiver loosely with paper or cardboard. Watch the action, as
the Na decomposes H2O. HOH + Na = NaOH + H. If the water be hot
the action is so rapid that enough heat is produced to set the H
on fire. That the gas is H can be shown by putting the Na under
the mouth of a small inverted t.t., filled with cold water, in a
water-pan. Na rises to the top, and the t.t. fills with H, which
can be tested. NaOH dissolves in the water.102. Properties.

Experiment 63.--(1) Test with red litmus paper the solutions
obtained in the last two experiments. (2) To 5cc.of alum