BENZOIC ACID, an organic acid, be longing in the aromatic series and having the formula Calia.COOH. It occurs in benzoin gum and in certain other resins and balsams. It may be obtained also from the hippuric acid that occurs in the urine of the horse and other herbivorous animals by boiling that acid with concentrated hydrochloric acid. Benzoic acid is used as a mordant in calico printing, and in the manufacture of aniline blue. It is also used in medicine and as a pre servative agent for anatomical specimens. The largest use of benzoic acid, however, is as a food preservative. With its salt, soda ben zoate, it is used in huge quantities in catsups, sauces, jellies, jams, fruit syrups, sausages and other chopped meats, cider, soft drinks and many other similar food preparations. This use was questioned by the U. S. Chemistry Bureau and led to an elaborate series of experi ments upon a so-called *poison squad* of young men. The report, published as Bulletin 84 of the Bureau, was to the effect that benzoic acid and its salts were distinctly deleterious to health and should not be permitted in foods. A referee board of eminent physiological chem ists were called to confirm or refute the Chem istry Bureau's findings, and they decided that the largest amount that would be eaten in the ordinary use of such preserved foods would not be injurious to health. Upon this decision the government permits such use of benzoic acid and benzoate of soda on condition that the proportion used is stated plainly on the label covering the goods. Many States, however, prohibit it absolutely; others restnct its use iri foods to very narrow limits.
The benzoic acid that is used for medical purposes is obtained by sublimation, through a paper filter of benzoin gum over a sand bath, at a temperature of about 340° F. When so prepated, the acid has a pleasant, vanilla-like odor, which is imparted to it by a trace of an aromatic oil that comes over with it from the gum. For most of the purposes for which it is used in the arts, benzoic acid is formed by chlorinating toluene. The resulting benzotri chloride is converted into benzoic acid by ox idation with dilute nitric acid in boilers pro vided with mechanical stirrers. Hydrochloric
acid is liberated and the benzoic acid is recrys tallized or distilled under vacuum. Benzoic acid is also made from benzonitrile (C.H..CN) obtained from the *middle oils* or carbolic oils in coal-tar distillation. After washing the carbolic fraction with dilute soda lye to re move the phenol and cresol, the remaining oil is placed in a jacketed vessel. Caustic soda lye of a specific gravity of 1,400 is added in quan tity about double the benzonitrile content, and the mixture agitated. Steam is passed in as long as ammonia is evolved in quantity. The still then contains an upper oily layer and a lower alkaline layer. The latter is neutralized with carbonic acid or a mineral acid, and after the remaining traces of phenol and resinous matters are removed, the resulting solution of sodium benzoate is decomposed while hot by adding an excess of acid. Upon cooling, pure benzoic acid separates in white crystals.
Benzoic acid dissolves in hot water, but crys tallizes out, upon cooling, in needles or pearly prisms. It is soluble in ether, alcohol and ben zene. It melts at 250° F., boils at 480° F., and may be sublimed at intermediate temperatures. Its salts are called ubenzoates.* The methyl, ethyl, isobutyl and amyl esters of benzoic acid are used in making synthetic perfumes and flavors.
In medicine benzoic acid and its salts, the benzoates (sodium, ammonium, lithium) are widely employed for diseases of the bladder and of the mucous membranes of the lungs. They are also used as intestinal germicides. Benzoic acid has marked bactericidal properties, and may be used for sterilizing purposes. Taken into the intestines it prevents excessive bacterial decomposition; absorbed into the blood it is partly broken up, and in the Icid neys is eliminated in part as hippuric acid, ren dering the urine acid. It is therefore useful in alkaline fermentations of the urine, particularly in cystitis, pyelitis, etc. Benzoic acid is partly eliminated by the lungs, here acting to increase the amount of mucus, it is therefore used to loosen the mucus in tight coughs. As a parasi ticide, benzoic acid is very valuable in scabies. Benzoates are practically useless in gout.