BORIC ACID 209Procedure: Dissolve 96 grams of borax in 175 cc. of boiling water.
Calculate the volume of 12 N HC1 required to liberate the boric
acid completely. Add this amount in small portions to the boiling
solution, stirring after each addition. When all the acid has been
added, test a drop of the solution with methyl orange. If an acid
test is not obtained, add 12 N HC1 in 2-cc. portions until a decided
pink color is obtained. Finally add an extra 2-cc. portion. Cool
the solution in a pan of tap water to 15° or below, and filter, using
suction. Press all the liquid possible out of the crystals. Test
the filtrate with methyl orange, and if it is not distinctly acid,
add enough 12 N HC1 to make it so. Add any boric acid thus pre-
cipitated to the main product. Pour 15 cc. of cold water over the
cake of crystals in the filter, and allow it to soak in, then drain
it off with suction. Dissolve the crystals in 300 cc. of boiling dis-
tilled water. Filter hot, without suction, into a clean 600-cc.
beaker. (See Note 4 (c), page 7.) Heat the solution, and com-
pletely dissolve any crystals of boric acid which may have sepa-
rated. Wrap the beaker in a towel held in place by a rubber
band. Cover it with a watch glass, and set it in your locker to
crystallize. Collect the crystals and let them dry at room tem-
perature on a paper towel. If the filtrate is evaporated to one-
third of its volume, a second crop of crystals will be obtained.
Dissolve a small amount of your product in distilled water, and
test it for chloride ion.
QUESTIONS- Explain the relations between orthoboric acid, metaboric
acid, tetraboric acid, and boric anhydride. Experiment: Place
a few grams of boric acid on a watch glass upon the steam table
(100-110°) and leave for \ hour. What is formed? What
would be formed if the acid were heated to 140°? Suspend a
little of the acid in a loop of platinum wire, and heat in the Bunsen
flame. What is formed? - Experiment: Place a few crystals of boric acid in a small
porcelain dish, cover them with 5 cc. of alcohol, set fire to it. Ob-
serve the color of the edges of the flame, especially when stirring
and when the alcohol is almost burned out. Repeat, using borax
instead of the boric acid, and again, using borax moistened with
concentrated sulphuric acid.