"Take of benzoin, one pound. Put the benzoin into a proper vessel placed in a sand-bath, and the heat being gradually increased, sublime until nothing more ascends; press the sublimed matter wrapped in bibulous paper, and being separated from the oily parts, sublime it again.

1 Henry's Aromatic Vinegar is a solution of camphor, and some essential oil, in acetic acid.

2 Phillips.

Edinburgh.

"Take of benzoin, twenty-four ounces; subcarbonate of soda, eight ounces; water, sixteen pounds. Triturate the balsam with the subcarbonate; then boil them in the water for half an hour, stirring them constantly, and strain. Boil the residue of the balsam in other six pounds of water, and strain. Mix the strained liquors, and evaporate to two pounds: filter again, and drop in diluted sulphuric acid as long as any precipitation is produced.

"Dissolve the precipitated benzoic acid in boiling water: strain the liquor whilst it is hot through linen, and set it aside to crystallize. Wash the collected crystals with cold water; then dry and preserve them for use."

Dublin.

"Take of benzoin Jive parts; fresh burnt lime, and muriatic acid, of each one part; water two hundred parts. Rub the benzoin with the lime, then boil the mixture in one hundred and thirty parts of water, for half an hour, stirring constantly with a spatula, and leaving the vessel at rest, decant the liquid when it is cold. Boil the residue in seventy parts of water, and again decant the liquid when it is cold. Mix the liquors, and boil to one half; filter through paper, and when cold, drop in gradually the muriatic acid. Finally, pour off the fluid, put the precipitated powder, previously washed in a small quantity of cold water, and dried with a gentle heat, in a proper vessel, and sublime the benzoic acid with a moderate fire."

Syn. Acide Benzoique (F.), Benzoesaure ( G.), Benzoin zuur (Dutch), Acido Benzoico (I.).

The process of the London college is nearly the same as that recommended by Chaptal: but although a greater quantity of the acid is thus procured, yet, if the fire be not very nicely regulated, the portion of empyreumatic oil volatilized, which gives the acid the peculiar odour of the benzoin, and a yellowish tinge is so great, that it cannot be entirely separated from it, even by the second sublimation after pressure between bibulous paper.1 The Edinburgh process is that of Gren, which is a modification of that of Scheele, published in 1775.2 Carbonate of soda separates the benzoic acid from the resin, with which it is united in the balsam, combines with it, and forms a benzoate, which is dissolved in the water; whilst at the same time a small portion of resin is also dissolved, and

1 This acid was originally obtained by sublimation. It was described under the name of flowers of benzoin by Blaise de Vigeneve, in 1608. Thompson's Chy-mistry, 4th edit. 289. 2 Scheele, i. 124.* gives the solution a yellow colour. This benzoate is decomposed in its turn by the sulphuric acid, which combines with the alkali, and forms a sulphate; whilst the benzoic acid that is set free, being insoluble in cold water, precipitates in the form of a brownish powder. A subsequent sublimation frees the acid of this colour, and gives it the crystallized form and brilliant appearance of the acid obtained by sublimation, without any adhering oil.

The Dublin process is a modification of that of Scheele. The lime unites with the acid of the benzoin, and forms a benzoate, which is decomposed by the hydrochloric acid, and precipitates the insoluble benzoic acid thus set free. The subsequent sublimation purifies and crystallizes the acid.1

Benzoic acid may also be extracted from the other balsams: it has been detected by Vogel in the flowers of Trifolium melilotus officinalis; and is also found in the urine of the cow and that of other ruminantia.

Qualities. - Benzoic acid, when perfectly pure, is inodorous; but as it is usually found in the shops, it has a slight aromatic odour2: its taste is pungent, sweetish, acrid, and acidulous. The pure sublimed acid is in feathery or flocculent crystals, soft to the touch, and not pulverulent, of a beautiful whiteness, and a silky lustre. Its specific gravity is 0.657. When heated, it melts, emits a suffocating acrid vapour, and in a strong heat burns with a white flame. Benzoic acid is soluble in twenty-four times its weight of boiling water; but the water lets fall nineteen-twentieths in cooling. Cold alcohol takes about one half its weight; boiling alcohol its own weight of this acid; the addition of water precipitates the acid. It is also soluble in hot acetic acid; and also without change in concentrated sulphuric and nitric acids. With the alkalies, earths, and metallic oxides, it forms benzoates, which are not used in medicine. According to Berzelius, it is a triple compound of 74.41 of carbon, 5.16 of hydrogen, and 20.43 of oxygen; or, according to Liebig and Wohler, of 14 equiv. of carbon = 85.68 + 5 of hydrogen = 5 + 3 of oxygen = 24, making the equivalent = 114.68. These chemists regard it as a compound of benzule, a compound of 14 eq. carbon = 85.68 + 5 hydrogen = 5 + 2 oxygen = 16, to which 1 eq. of oxygen being added, benzoic acid is formed.

The crystals contain no water.

Medical properties and uses. - This acid is stimulant; but, although it is retained by all the Pharmacopoeias, it is of little value as a remedy.

1 During its sublimation light is evolved.

2 To free it from the oil on which its odour depends, dissolve it in alcohol, and precipitate by water. Phil. Mag. xiv. 331.

Officinal preparations. - Tinctura Camphorae composita, L. D. Tinctura Opii Ammoniata, E.