PART III.

Acids.

Acidum aceticum tenae.

SG:i

is to be rejected; the five pounds that follow, will he the weakacetic acid. The distillation may be continued as long as acolourless acid comes over; but this, being too much burntand unfit for internal use, may be mixed with the pound whichiirst came over, and preserved for various chemical purposes."

Acetum distillatum, Dub. Distilled Vinegar.

" Take of wine vinegar, ten pints; distil with a gentle heatsix pints. The distillation must be performed in a glass vessel,and the first pound which comes over rejected."

The specific gravity of this acid is to that of water as 1006to 1000.

Sr/n. Vinaigre distille (F.), Distillirter Essig (G..), Aceto distillato (/.),Vinaigre distiiado (S.).

Of the three appellations given to this preparation in theBritish pharmacopoeias, that of the Edinburgh College onlyis unobjectionable. It is the acetic acid in a more dilutedstate than that in which it exists in vinegar, but purer ; beingfreed in a great degree from the mucilage, extractive, super-tartrate of potass, and other extraneous matters which vinegarcontains. 1 The distillation on a large scale is often conductedin the common copper still, or in a tinned still with a pewterworm ,• but both these practices, as they are apt to give danger-ous metallic impregnations to the product, are highly repre-hensible, when the distilled vinegar is to be employed formedicinal purposes.

In performing the process, it is more important to avoidcarrying the distillation too far than to reject the first eighthpart which comes over; for although this is undoubtedlyweaker, and contains a small portion of alcohol, yet it retainsabout one-twelfth * of the whole quantity of the real acid ob-tained : but by continuing the process a little too long, thewhole product acquires an unpleasant empyreumatic flavour.This is avoided by changing the receiver rather before thequantity ordered has been obtained; and, if to the residue beadded an equal quantity of hot water and half an ounce of re-cently burnt animal charcoal', for every pint of fluid in theretort, the distillation may be recommenced, and an additionalportion of the diluted acid obtained, equally pure and strongas the former. x\t the end of the operation, when dilutionhas not been employed, the residue is a deep red colouredliquor, strongly acid, very empyreumatic, and which depositssupertartrate of potass.

Qualities. — Distilled vinegar has a fainter and less agreeable

1 See Acetiim, Part II. t London Medical Review, No. x. 125.

5 Animal charcoal is made by calcining bones in a crucible, to which is luted aperforated cover. When no more flame issues from the aperture, it must beclosed, and the heat raised for half an hour.

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