210 ELEMENTS OF GROUP IIIWhat causes the green color of the flame, and why is it not
observed with borax alone?
Repeat if necessary the last part of Experiment 1, noticing the
color imparted to the flame while the orthoboric acid is first
melting, and again when a clear bead of boric anhydride is obtained.
What conclusions can you make from these experiments regard-
ing the volatility of boric acid and of boric anhydride?- What effect has a solution of borax upon litmus? Explain
what is thus shown regarding the strength of boric or tetraboric
acid. Explain why litmus will not be turned a bright red until
more than 2 moles of HC1 have been added to 1 mole of borax. - How can boron chloride be prepared? How does this sub-
stance behave when treated with water? How would it behave
if boron were a strongly metallic element?
PKEPABATION 24
SODIUM PERBORATE, NaBO 3 -4H 2 O
At least three boric acids of the definite compositions shown
by the formulas H3BO3, HBO2, H2B4O7 can be prepared in the solid
form. These are all obtainable from the anhydride B 2 O 3 , and
they differ only in the degree of hydration of the B2O3.
Hydrogen peroxide differs from water in that it possesses the
divalent negative radical O2 instead of the ordinary divalent 0
radical of water. (Compare page 160.)
Peroxides such as BaO 2 possess the same O 2 radical as hydro-
gen peroxide and exhibit similar oxidizing properties. There is
also a large number of acids and salts known in which an O2 group
takes the place of the single 0 atom in the ordinary compound.
These also possess the oxidizing properties of peroxides. One of
the most easily prepared of these is sodium perborate NaBO 3
which bears the same relation to sodium metaborate NaBO 2 that
hydrogen peroxide does to water. A solution prepared with equi-
formal amounts of H3BO3 and NaOH contains the proportions of
acid and base to yield NaBO 2. But if this solution is evaporated
to the point where crystals separate, we do not obtain NaBO2 but
rather borax Na 2 B4O7-10H 2 O, and the remaining solution contains
a higher proportion of base. If, however, H 2 O 2 is added to the
dilute sodium metaborate solution, the sparingly soluble hydrated
sodium perborate NaBO 3 -4H 2 O crystallizes out. This salt when