Synonym. Acidum Aceticum. Edin. Monohydrated Acetic Acid.

Prep. This is prepared by distilling acetate of soda, from which the water has been expelled by heat, with sulphuric acid, by which means sulphate of soda is formed, and acetic acid distils over. If the product contains any sulphurous acid, when tried by the iodate of potash and starch test mentioned above, it is shaken with black oxide of manganese and redistilled. Any sulphurous acid is thus converted into sulphuric acid, and remains in combination with the manganese.

Prop. & Comp. A colourless liquid, converted when cooled to nearly 32° into colourless prismatic crystals. Composition HO, C4 H3 O3, or an acetate of water. Sp. gr. 1.065, which is increased by adding 10 per cent. of water. Dilution increases the density of acetic acid until nearly one-third of its weight of water has been added, when it contains HO, C4 H3 O3 + 2 Aq. On further dilution, the density diminishes in the usual manner. In consequence of this anomaly, the density alone cannot be relied on as a test for the strength of acetic acid, as between 1.063 and 1.077 the same density may indicate two very different strengths; monohydrated acetic acid and the same acid diluted with an equal weight of water having both the sp. gr. 1.063. A fluid drachm of glacial acetic acid requires for neutralization 97 measures of the volumetric solution of soda. The absence of sulphurous acid is indicated by the iodate of potash and starch test.

Off. Prep. It is used in the preparation of Mistura Creasoti.

Therapeutics. Glacial acetic acid acts as a caustic irritant, vesicant, and escharotic. It is chiefly used as an external application; but diluted with water may be used for the same purposes as dilute acetic acid.

Acetum. Vinegar (French). Impure dilute acetic acid, prepared from French wines by the acetous fermentation. [Prepared by fermentation. U. S.] Prep. The alcohol contained in the wine, under certain conditions, absorbs oxygen, and is converted into acetic acid, which is contained in the vinegar. The change is thus shown: alcohol (C4 H6 O2) + O4= acetic acid (HO, C4 H3 O3) + 2 HO.

Prop. & Comp. A liquid of a straw colour, having an agreeable acid odour and taste; sp. gr. from 1.008 to 1.022. It is a little stronger than British vinegar, about one-sixth, and when ammonia is added in excess to it, some turbidity is usually produced, and a purple colour, due to the development of the colouring matter of the wine. British vinegar, which was formerly officinal, contains about 5 per cent. of real acid, together with colouring matter, mucilage, and a small amount, 1/1000 part by weight, allowed by law, of sulphuric acid.

Therapeutics. The action of vinegar is the same as that of dilute acetic acid of equal strength.

Dose. Of acetum 1 fl. drm. to 3 fl. drm. diluted.

Adulteration. Sulphuric acid may be added to vinegar, and metallic impurities may be present from the vessel in which it is kept. It should be scarcely affected by chloride of barium, or oxalate of ammonia, and not at all by sulphuretted hydrogen.