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■ELEMENTS OF MATERIA MEDICA.

Properties. — {a.) Of Glacial Acetic Acid . —This is the protohydratedacetic acid, which is crystallized solid at about 40°. F. It is thestrongest acid procurable, but, as it has no uses in medicine, will notrequire further notice.

(a.) Of the Acetic Acid of the Pharmacopoeia . —This is a limpid,colourless liquid, having a pungent but agreeable odour, and an acridtaste. Its sp. gr. is l - 048. It possesses the usual properties of an acid,such as reddening litmus, causing effervescence with the alkaline orearthy carbonates, and saturating bases. It is volatile, and by heatevolves an inflammable vapour.

(c). Of the Distilled Vinegar of the Pharmacopoeia . —This contains,besides acetic acid and water, some alcohol and an organic substancederived from the mucilage of the vinegar. Hence when it is saturatedwith alkalies the solution becomes brown by heat, and deposits a dark-coloured substance. Mr. Phillips states that a mixture of 15 parts byweight of the officinal acetic acid and 85 of water is equal in strength todistilled vinegar.

Characteristics. —Free acetic acid is known by its peculiar odourand by its volatility. Its vapour reddens litmus, and fumes with ammonia.This acid produces no precipitate with lime water, with solutions of thebarytic salts, or with a solution of nitrate of silver. It forms with potasha very deliquescent salt.

The neutral acetates are all soluble save those of molybdenumand tungsten. The acetates of silver and protoxide of mercury areslightly soluble. The acetates are known by the acetic odour whichthey emit on the addition of sulphuric acid, and by the white lamellarand pearly precipitates which many of them produce with either thenitrate of silver or the protonitrate of mercury. All the acetates aredecomposed by heat, and give results which vary somewhat accord-ing to the nature of the base. Some of the acetates, as those ofpotash, lead, and copper, evolve when heated an inflammable fluidcalled acetone or pyro-acetic spirit, whose composition is C :J . H 3 . O'.

Composition. —Anhydrous or real acetic acid consists of carbon,hydrogen, and oxygen, in the following proportions :—

Eq. Eq.Wt. Per Cent. Prout. Berzelius .

Carbon. 4 . . . . 24 ... . 47*06 .... 47*05 .... 46*83

Hydrogen. 3 . . . . 3 . . . . 5*88 .... 5*88 . . . '. 6*35

Oxygen. 3 . . . . 24 ... . 47*06 .... 47*07 .... 4682

Anhydrous Acetic Acid. 1 . . . . 51 ... . 100*00 .... 100*00 .... 100*00

The acetic acid of the London Pharmacopceia consists of water andpure acetic acid. As 100 grains of it saturate 87 grains of crystallizedcarbonate of soda, it must contain 30 8 per cent, of pure acetic acid(Phillips, op. cit.). This is very nearly one equivalent of acid to thirteenequivalents of water.

Eq. Eq.Wt. Per Cent. Phillips.

Anhydrous Acetic Acid. 1 51 30*35 30*8

Water. 13 117 69*65 69*2

Acetic Acid (Ph. L.). 1 168 100*00 100*0

Purity.— The foreign matters likely to be present in acetic acid areexcess of water, sulphuric, hydrochloric, or nitric acid, copper, lead, tin,