5. They may be divided into four orders, as, 1, Crystallizable and volatilizable, such as the acetic, benzoic, sebacic, succinic, moroxylic, camphoric, and oxalic acids, composed of hydrogen, carbon, and oxygen; 2, Crystallizable and not volatilizable, as the mellitic, tartaric, citric, kinic, and saclactic acids, composed of carbon, hydrogen, and oxygen, to which may be added the uric and laccic acids, the former of which contains also azote; 3, Not crystallizable, as the malic, suberic, and formic acids, containing carbon, hydrogen and oxygen; and 4, Colorific, as the gallic, and prussic acids, the former of which is composed of carbon, hydrogen and oxygen, and the latter of carbon, hydrogen and azote: to which some add sulphuretted hydrogen or hydrothionic acid of the Germans, composed of sulphur and hydrogen.

SECTION XIX.

OF ACETIC ACID.

Experiment 1. Mix in a glass retort two ounces of very strong vinegar with four ounces of dried muriate of lime, and draw off a portion of the acid by distillation. Mix this with the like quantity of muriate of lime, and distil again. The first products now will be acetic acid.

Rationale. The muriate of lime attracts the water, with which the acetic acid is diluted, in the form of vinegar, and the distillation separates the colouring or other fixed ingredient of the vinegar. Or,

Experiment 2. Take one part of acetate of potash, put it into a tubulated retort, lodged in a sand-heat, and pour gradually upon it half its weight of sulphuric acid. A violent action takes place, and part of the acetic acid becomes liberated in the form of white vapours. After the spontaneous action has ceased, distil with a

gentle heat, and acetic acid will be obtained in a considerable quantity.

Rationale. In the acetate of potash the acetic acid is already combined; the object, therefore, is to separate it in a distinct state. This is accomplished by using sulphuric acid, which unites with the alkali, forming sulphate of potash, whilst the acetic acid distils. Or, Experiment 3. Put acetate of copper into a retort, and distil; acetic acid will come over.

Rationale. In this salt the acid is combined with the oxyd of copper: by distillation this salt is decomposed; for the caloric applied separates the acid, leaving an oxyd of copper in the retort.

Experiment 4. If vinegar be introduced into a retort and distilled, a product will be obtained called acetous acid.

Rationale. The object of distillation is only to separate the colouring matter; the liquor obtained is not therefore the acetic or radical vinegar (as it is sometimes called) but the acetous acid, being nothing more than the acetic acid diluted.

Remark. Acetous acid is formed by the fermentation of wine, on which account it is called vinegar. However, wine is not indispensably necessary for its production, as it is found in the urine of animals, &c. The vinegar produced during fermentation is far from being pure acetous acid, but may be obtained so by distillation.

The acid principle in all these acids is the same. They differ merely in the concentration of that acid. The specific gravity of vinegar varies from 1.0135 to 1,0251. Vinegar may be preserved for a long time by previously boiling it. Besides acetic acid and water, vinegar contains several other ingredients, such as mucilage, tartar, or colouring matter, and often two or more vegetable acids. Acetous acid, or distilled vinegar, exposed to the action of cold, is considerably concentrated, provided the cold be sufficient to freeze it. The process mentioned above for obtaining acetic acid by the distillation of acetate of copper, was known to the alchemists, who called the product vinegar of ve

R

Tilis.

This acid is transparent and colourless, and has a peculiar aromatic flavour. That it is considerably stronger than the acetous acid is evident for its specific gravity; that of the acetous is 1.007 and the acetic 1.080. It is extremely pungent and acid. It is very volatile, and is inflammable. It may be obtained in a crystallized state, according to Lowitz, in the following manner:

Experiment 5. Mix distilled vinegar with well burnt charcoal, so as to form it into a paste, and expose the mixture to a heat not above 212°. By applying a stronger heat, having the mixture in a retort, very strong acid is obtained. This will readily crystallize.

SECTION XX.

OF BENZOIC ACID..

Experiment 1. If gum benzoin be pulverised, and put into an earthen pan, after which a paper cover attached; the whole then exposed to a sufficient heat in a sand bath, the flowers of benzoin, or benzoic acid, will be obtained; and,

Experiment 2. If the flowers, thus produced, be dissolved in water, the solution evaporated and crystallized, the purified salt of benzoin of the dispensatories will be prepared.

Experiment 3. If storax, tolu, or any other balsam be treated as in Experiment 1, the same product will be formed.

Remark. As benzoic acid exists ready formed in the natural balsams, some of which contains more than others, in which it is always combined with resin, it may be separated either by sublimation, or by combining it with a salifiable base. The following beautiful experiment may be made with benzoin by sublima

tion:

Experiment 4. Into a large glass jar, inverted upon a flat brick tile, and containing near its top a branch of

fresh rosemary, or any other such shrub, moistened with water, introduce a flat thick piece of heated iron on which place some gum benzoin in gross powder. The benzoic acid, in consequence of the heat, will be separated, and ascend in white fumes, which will at length condense, and form a most beautiful appearance upon the leaves of the vegetable.

Experiment 5. If benzoin be boiled with a solution of carbonate of soda, the solution filtered, then suffered to cool, and sulphuric acid dropped into it as long as any precipitate is produced, benzoic acid will be formed.

Rationale. The benzoic acid, of the gum benzoin, first unites with the soda of the carbonate, forming benzoate of soda, and the sulphuric acid then combines with the soda into a sulphate of soda, whilst the benzoic acid is precipitated.

Remark. Benzoic acid prepared in either of the above modes, is a fine light matter, possessing an acrid, hot and bitter taste. Its odour is aromatic.

Its specific gravity is 0.667. It is easily volatilized by heat. It is soluble in hot water; also in alcohol and the stronger acids. It is not acted upon by oxygen gas, or by any of the simple combustibles or incombusti

bles.

SECTION XXI.

OF SEBACIC ACID.

Experiment 1. Distil hog's lard, wash the product with hot water, and drop into it a solution of acetate of lead, till it occasions no further precipitate. Collect this precipitate, wash it, and dry it. Having done this, pour over it sulphuric acid and heat it; a substance resembling fat will then appear on the surface. This being collected, dissolved in boiling water, and suffered to cool, crystallizes, and is sebacic acid.

Rationale.

Distillation separates the sebacic acid, which is precipitated by acetate of lead; the sebate of lead is then decomposed by sulphuric acid, which unites with the lead, and the sebacic acid is disengaged.

Remark. Sebacic acid exists in a concrete form. It crystallizes in needles. It is void of odour. Its taste is slightly acid. When heated it liquefies like tallow, and is not volatile. It is soluble in cold water. Boiling water dissolves it very readily. It is also soluble in alcohol. It precipitates the acetates and nitrates of silver, mercury, and lead, and the acetates of lead and mercury. It does not precipitate lime-water.

Berzelius asserts, that this acid, in most of its properties, coincides with benzoic acid.

SECTION XXII.

OF SUCCINIC ACID.

Experiment 1. Fill a matrass half full of amber, lute to it an alembic, and distil with a gradual heat, till drops of oil fall from the beak of the alembic. Then separate the solid acid which has sublimed, dissolve it in water, filter the solution, and suffer it to crystallize. Repeat these latter operations till the salt is nearly colourless; or this trouble may be saved by abstracting from it a small quantity of nitric acid, which renders it a beautiful white: one dram of nitric acid is sufficient to one ounce of succinic acid of commerce.

Remark. As succinic acid exists ready formed in amber, mere distillation will separate it.

Succinic acid exists in a solid form. Its crystals are colourless, four-sided, oblique plates, which are permanent in the air. It has a strong acid taste. It is soluble in 24 parts of cold, and in two of boiling, water. It is soluble in hot alcohol. It may be volatilized by heat, but suffers a partial decomposition.