Benzoic Acid

Benzoic Acid, or the Flowers of Benzoïn, has been known since the beginning of the 17th century, and occurs naturally in many balsamiferous plants, and especially in benzoïn gum, from which it may be readily obtained by several processes. The simplest is as follows: The coarsely-powdered resin is gently heated in a shallow iron pot, the mouth of which is closed by a diaphragm of coarse filter-paper. Over this is tied a covering of thick paper somewhat like a hat. The porous filter-paper allows the vapours of benzoic acid to pass through it, but keeps back the empyreumatic products. At the end of the operation, the hat-like cover is found lined with a crystalline sublimate of benzoic acid which is nearly pure, being mixed only with traces of a volatile oil, which gives it a pleasant smell, like vanilla. The benzoic acid thus prepared is the best for pharmaceutical purposes. Benzoic acid is also prepared from the urine of graminivorous animals. The urine is allowed to putrefy, then mixed with milk of lime and filtered. The filtrate, concentrated by evaporation, gives with hydrochloric acid a precipitate of benzoic acid. Benzoic acid thus prepared is cheaper, but always smells of urine. By subliming it with a small quantity of benzoïn gum, the pleasant vanilla-like smell may, however, be imparted to it also. Benzoic acid is always in the form of snow-white, glistening, feathery crystals, with a fairy aspect of lightness, having a warm, acrid, and acidulous taste. It is readily dissolved by alcohol and ether, but sparingly soluble in water, which, however, dissolves it readily on the addition of borax or phosphate of soda. Benzoic acid is one of the materials present in Tinctura Camphore Composita, and has been administered in chronic bronchial affections, its value being due to its locally stimulating properties. It has also been used largely in genito-urinary diseases. Benzoic acid taken into the stomach increases within three or four hours the quantity of hippuric acid in the urine. It forms a numerous class of compounds with the oxides of the metals, lime, &c., called benzoates. The chemical formula for crystallised benzoic acid is $C\_6H\_5COOH$. Oil of bitter almonds (hydride of benzoyl) is the aldehyde of benzoic acid (see ALDEHYDES), and the corresponding alcohol, benzoic or benzylic alcohol, is also known.