Characters. - Transparent, colourless, six-sided plates, slightly unctuous to the touch, permanent in the air, odourless, having a cooling, bitterish taste and a feebly acid reaction; in solution turning blue litmus-paper red and turmeric paper brown, the tint in the latter case remaining unaltered in presence of free hydrochloric acid. The alcoholic solution burns with a flame tinged with green.

Preparation. - Vide p. 566.

Impurities. - Sulphates, chlorides, lead, copper, iron, etc, calcium and sodium salts.

Tests. - An aqueous solution of boric acid should not be precipitated by test solutions of chloride of barium, nitrate of silver with nitric acid, sulphide of ammonium, or oxalate of ammonium. A fragment heated on a clean platinum wire in a non-luminous flame should not impart to the latter a persistent yellow colour.

Dose. - 5-30 grains.

Officinal Preparation.

B.P

Unguentum Acidi Borici. - Boric acid 1, soft paraffin 4, hard paraffin 2.

Action and Uses. - From its power of turning turmeric brown it is used as a test for this substance in rhubarb. It has the power of destroying low organisms, and has therefore been used as an antiseptic application to wounds either in the form of a solution (1 part in 20 of hot water) or of an ointment. The antiseptic ointment originally recommended by Lister consisted of a mixture of the acid (1) with white wax (1), paraffin (2), almond oil (2). This is rather hard, and a better ointment consists of the powdered acid (3), paraffin (5) and vaseline (10). The relative proportions of these may be varied according to the temperature, more or less paraffin being added according as the temperature is high or low. Boric acid lint is a useful antiseptic dressing for small wounds and ulcers; and as an antiseptic hot fomentation in small abscesses, whitlows, etc. The powdered acid, mixed with starch, forms a useful dusting powder for infants, and lessens the foetor of perspiration. When given internally it is said to be occasionally useful in cases of vomiting in somewhat the same way as sulphurous acid, and it has also been given along with ether in septic diseases. Boro-glyceride, discovered and patented by Barff, is made by heating 92 parts of glycerine with 62 of boric acid. A solution of 1 in 40 of water is recommended as a powerful antiseptic. It is used to preserve food, and as a lotion for the treatment of wounds and in purulent ophthalmia.1