Boric acid, also known as boracic acid and arthoboric acid, is a very weak acid with the formula H3BO3, often used as a mild antiseptic. Chemically, it acts as a tribasic acid—an acid that can dissociate successively to produce three hydrogen ions in solution. However, because it dissociates to such a small extent, it is a very weak acid that is actually used in water solution as an eye wash. Pure boric acid is a colorless, odorless, white powder or transparent crystals that melt at about 340°F (171°C). Boric acid loses water as it is heated, changing first into metaboric acid (HBO2) and then into pyroboric acid (H2B4O7). The three acids can be thought of as hydrates of boric oxide (B2O3). Orthoboric acid is fairly soluble in water (especially hot water), alcohol, and glycerine.
Boric acid has a wide variety of industrial applications. It is used in the manufacture of heat-resistant borosilicate glass and other ceramics, such as crockery, porcelains, enamels, and artificial gemstones. It also used in waterproofing wood and fireproofing textiles. It also finds application as an insecticide for cockroaches and black carpet beetles and as an fungicide on citrus fruits.
Its use in the last of these applications is carefully monitored, however, because of the compound's toxicity. When swallowed, boric acid can cause nausea, vomiting, diarrhea, and other intestinal problems. In large doses, it can cause coma and death. The toxic level of boric acid in infants can be less than 0.2 oz (5 g) and in adults, from 0.2 oz (5 g) to 0.7 oz (20 g).
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