"Take one gallon of vinegar, distil the vinegar from a glass retort, placed in a sand-bath, into a glass receiver. Preserve for use the seven pints which are first distilled."

Acidum aceticum tenue, Edin. Weak Acetic Acid.

"Distil eight pounds of vinegar in glass vessels, with a gentle heat. The pound which first comes over, being too watery, is to be rejected; the five pounds that follow will be the weak acetic acid. The distillation may be continued as long as a colourless acid comes over; but this being too much burnt, and unfit for internal use, may be mixed with the pound which first comes over, and preserved for various chemical purposes."

Acetum distillatum, Dub. Distilled Vinegar.

"Take of wine vinegar ten parts (by measure); distil with a gentle heat eight parts. The distillation must be performed in a glass vessel, and the first part which comes over rejected."

The specific gravity of this acid is to that of water as 1005 to 1000.

Syn. Vinaigre distille (F.), Distillirtcr Essig (G.), Azynagtige zuur, (Dutch), Aceto distillato (I), Vinaigre distilado (S.).

In this preparation the acetic acid is in a purer but more diluted state than that in which it exists in vinegar; being freed in a great degree from the mucilage, extractive, bitar-trate of potassa, sulphuric acid, colouring matter, and other extraneous matters which vinegar contains.1 This distillation is now conducted on a large scale, as the greater part of the fluid sold as distilled vinegar, and that employed for medicinal purposes, is merely diluted pyroligneous acid.

In performing the above processes, it is more important to avoid carrying the distillation too far than to reject the first eighth part which comes over; for although this is undoubtedly weaker, and contains a small portion of alcohol and pyro-acetic acid, yet it retains about one twelfth 2 of the whole quantity of the real acid obtained; thence the London College now orders it to be kept. By continuing the process a little too long, the whole product acquires an unpleasant empyreumatic flavour. This is avoided by changing the receiver rather before the quantity ordered has been obtained; and, if to the residue be added an equal quantity of hot water and half an ounce of recently burnt animal charcoal, for every pint of fluid in the retort, the distillation may be recommenced, and an additional portion of the diluted acid will be obtained, equally pure and strong as the former. At the end of the operation, when dilution has not been employed, the residue is a dark brownish red coloured liquor, strongly acid, very empyreumatic, and which deposits bitartrate of potassa.

Mr. Brande justly regards as an improvement in the distillation of vinegar the employment of the heat of high-pressure steam, instead of that of an open fire; as both the risk of empyreuma is prevented, and "a larger portion may usually be distilled off before any foreign flavour is perceptible."3

Qualities. - Distilled vinegar has a fainter and less agreeable odour than common vinegar; a grateful, not strong, acid taste; is limpid and colourless; and of a specific gravity varying from 1.007 to 1.0095. It should evaporate completely when heated; and afford no precipitate with acetate of lead, or nitrate of silver, or iodide of lead, Neither hydrochloric acid nor ammonia should change its colour. After a plate of silver has been digested in it, it should afford no precipitate with hydro-sulphuric acid. One hundred grains should require thirteen grains of crystallized carbonate of soda for their saturation. It dissolves the gum resins and the active principles of plants, such as those of the squill and the meadow-saffron; and forms acetates with the alkalies and several of the metallic oxides. One hundred parts of distilled vinegar should be saturated by 13 grains of carbonate of soda in crystals, or contain of acetic acid 4.6 + water 96.58 parts. It is sometimes adulterated. Sulphuric acid is detected by a precipitate being produced on the addition of a solution of acetate of baryta; acetate of lead, by the solution of hydriodate of potassa, affording a yellow precipitate, or by a solution of sulphureted hydrogen, forming a dark-coloured precipitate; and acetate of copper, by the acid assuming a blue colour, when supersaturated with ammonia, or affording a brown precipitate with ferrocyanate of potassa.

1 See Acetum, Part II.

2 London Medical Review, No. x. 125.

3 Manval of Pharmacy, p. 92.

Medical properties and uses. - The same as those of common vinegar; but, as it is purer, and not liable to spontaneous decomposition, it is fitter for pharmaceutical purposes.

Officinal preparations. - Liquor Ammoniae Acetatis, L. E. D. Potassae Acetas, E. D. Sodae Acetas, D. Ferri Acetas, D. Plumbi Acetas, E. D. Liquor Plumbi Diacetatis, L. Acetas Opii, D. Acetum Colchici, L. Acetum Scillae, L. E. D. Oxymel, L. D. Oxymel Scillae, L. Oxymel Colchici, D. Oxymel Cupri Subacetatis, D.