Scheele’s wet method consisted in boiling benzoin in water and milk of lime, separating the resulting calcium benzoate while hot by filtration, and precipitating from the solution the benzoic acid by means of hydrochloric acid. The product is sometimes sublimed to give the appearance of the acid made by the dry method. This process yields about 13 per cent. 1/2.
A commercial grade known as German benzoic acid is prepared by mixing the urine of horses and cattle with an excess of lime, and evaporating the solution to about one-twelfth of its bulk. The resulting calcium hippurate is then supersaturated with hydrochloric acid, liberating hippuric acid, which is purified by animal charcoal or other means. Hydrochloric acid is then added to the purified hippuric acid and boiled one-half hour, when benzoic acid and glycocoll (CH2NH COOH) result. Benzoic acid obtained in this manner has a 2 fetid, urinous odor, and is purified by recrystallization or by sublimating it with a small quantity of benzoin.
Soluble, when pure, in about 500 parts of water, and in 2 parts of alcohol at 15° C. (59° F.), in 15 parts of boiling water, and in 1 part of boiling alcohol. Also soluble in 3 parts of ether, 7 parts of chloroform, and readily soluble in carbon disulphide, benzol, fixed and volatile oils, but sparingly soluble in benzin. Benzoic acid volatizes freely with the vapor of water. On heating it to 100° C. (212° F.) it begins to sublime. At 121.4° C. (250.5 F.) it melts, and at a higher temperature it is consumed without leaving a residue. The acid sublimed from benzoin has a lower melting point, and a greater solubility in water.
Benzoic acid has an acid reaction. On heating benzoic acid gradually with 3 parts of freshly slaked lime in a retort benzol is evolved. The acid is freely soluble in solutions of alkali hydrates. On carefully neutralizing such a solution, and adding ferric chloride T.S., previously diluted with 2 volumes of water, and neutralized, if necessary, by ammonia, a flesh- colored precipitate of ferric benzoate is produced. A solution of benzoic acid in pure, cold, sulphuric acid, when gently warmed, should not turn darker than light brown; if it is then poured into water the benzoic acid should separate as a white precipitate, and the liquid should be colorless (absence of readily carbonizable, organic matters). If 0.5 Gm. of the acid and 0.8 Gm. of calcium carbonate be mixed with a little water in a crucible, the mixture dried, gently ignited, and then dissolved in water, with the aid of nitric acid in slight excess, so as to obtain 20 Cc. of filtrate, the addition of silver nitrate T.S. to the latter should not produce much more opalescence (if at all) than is produced by the same reagent in a solution measuring 20 Cc. prepared by dissolving 0.8 Gm. of the same calcium carbonate in water with the aid of nitric acid (absence of more than traces of chlorine).
On warming 0.5 Gm. of the acid with 5 Cc. of water and 0.5 Gm. of potassium permanganate in a test-tube loosely stoppered and placed in a water-bath heated to about 45° C. (113° F.), then tightly stopping and cooling the test-tube with cold water, upon removing the stopper no odor of oil of bitter almond should be discernible (absence of cinnamic acid)” .
Benzoic acid is permanent at ordinary temperatures. If made from hippuric acid its appearance is often as fine, if not finer, than when produced from benzoin, but traces of a urinous odor can be detected in it. If the odor of benzoic acid resembles that of the sweat of horses it should be rejected. German benzoic acid is often a pure white, the object in later years having been to make it so that it will resemble that produced from the gum. Formerly the crystals produced by this process (artificially) were much the handsomest. It will be observed that though the Pharmacopoeia recognizes both the natural and artificial product its description of the acid is so constructed that it can apply only to the true product produced from the gum, thus practically ruling out the artificial acid. Benzoic acid gives rise to a line of more or less soluble salts known as benzoates.”
And that may be will give you some hints about the use of aromatic substances or urine. We will also see other ancient proceedings.
See also Starkey Pirotechnie & Volatilization of Alkalis and Nicolas Lefevre and the Benzoin Magisterium , on urine volatile salts see also Glaser and the Unladylike, but Volatile, Salt of Urine , Hollandus, How Urine Salts Extract a White and Red Dye ;