Boric Acid

Boric acid bp
mf h3bo3 -- m.wt 61.8 -- cas# 10043-35-3
definition
boric acid contains not less than 99.0 per cent and not more than the equivalent of 100.5 percent of h3bo3.
Characters
a white, crystalline powder, colourless, shiny plates greasy to the touch, or white crystals, soluble in water and in alcohol, freely soluble in boiling water and in glycerol (85 per cent).
Identification
a. Dissolve 0.1 g by gently heating in 5 ml of methanol, add 0.1 ml of sulphuric acid and ignite the solution. The flame has a green border.
B. Solution s (see tests) is acid.
Tests
solution s
dissolve 3.3 g in 80 ml of boiling distilled water, cool and dilute to 100 ml with carbon dioxide-free water prepared from distilled water.
Appearance of solution
solution s is clear and colourless.
Ph
the ph of solution s is 3.8 to 4.8.
Solubility in alcohol
dissolve 1.0 g in 10 ml of boiling alcohol. The solution is not more opalescent than reference suspension and is colourless.
Organic matter
it does not darken on progressive heating to dull redness.
Sulphates
10 ml of solution s diluted to 15 ml with distilled water complies with the limit test for sulphates (450 ppm).
Heavy metals
12 ml of solution s complies with limit test a for heavy metals (15 ppm).
Boric acid usp nf
h3bo3 -- 61.83
boric acid contains not less than 99.5 percent and not more than 100.5 percent of h3bo3, calculated on the dried basis.
Solubility in alcohol— one g dissolves completely in 10 ml of boiling alcohol.
Completeness of solution— one g dissolves in 25 ml of water, producing a clear solution.
Identification— it responds to the tests for borate.
Loss on drying— dry it over silica gel for 5 hours: it loses not more than 0.5% of its weight.
Heavy metals— dissolve 1 g in 23 ml of water, and add 2 ml of 1 n acetic acid: the limit is 0.002%.