as the fatal effects which have sometimes attended its use are doubtless chiefly owing to its contaminations. It should be colorless and free from a chlorous smell, or any unpleasant odor, when a few drops are evaporated on the hand. Chloroform is one of the most important representatives of a class of bodies, the vapor of which when inhaled produces temporary insensibility to pain, or anæsthesia; these substances are known as anæsthetics. CHAPTER XXVI. ORGANIC CHEMISTRY (CONTINUED). § 1. Acids. 546. A LARGE number of organic acids are known, some of which exist in a free state, as, for example, formic acid, which is secreted by ants and is found in nettles. These compounds constitute several series, which are all regarded as derived more or less directly from the hydrocarbons. Formic acid, CH,O,, is a clear, pungent, volatile, strongly acid liquid, which was first obtained by distilling the bod ies of red ants (Formica rubra) in water, hence its name formic acid. It is also found in human blood, urine, and other secretions, in the juices of many plants, and in the waters of certain mineral springs. 547. Acetic Acid, C,H,O,.-This acid is one of the most important organic compounds. It is the essential constituent of vinegar, which is merely a more or less impure solution of acetic acid, common table-vinegar containing from three to four per cent. Pure acetic acid is, at ordinary temperatures, a colorless, intensely sour liquid, having a pungent odor, and capable of raising a blister on the skin. It solidi 66 fies at or below 17° C. to a crystalline, ice-like body, known as glacial acetic acid," and boils at about 119° C. Vinegar is usually obtained by the spontaneous oxidation of dilute alcoholic liquors, saccharine solutions, etc. If, in the process of its manufacture, the air comes in contact with only a small portion of the liquid, months may be required to produce the change. Wood-vinegar, or pyroligneous acid, is obtained by the destructive distillation of wood, dry beech-wood being the best, a pound yielding nearly half a pound of the acid. It is a brown liquid, with a strong smoky taste and odor. It is extensively used to form salts-the acetates used by dyers. 548. Butyric Acid, CH,O,, is prepared by allowing a mixture of sugar, chalk, and cheese, to ferment. It is found in small quantity in butter, in perspiration, in some plants, and in the juice of human flesh. It resembles acetic acid in appearance, has a peculiar rancid odor, and is soluble in water. Glycocholic Acid, C,H,O,, constitutes the great mass of the resinous matter of ox-bile; it forms silky white, needle-shaped crystals, of a bitter-sweet taste, which are soluble in water and alcohol, and have an acid reaction. 549. Lactic Acid, C,H,O,.—This acid is so called because it occurs in sour milk. It is formed from sugar by lactic fermentation, and is a colorless, sirupy, very acid liquid. Succinic acid, CHO,, is also one of the products of the fermentation of sugar (538), and is obtained by the distillation of amber. It occurs in certain resins, in wormwood, and in small quantities in animal juices. Intimately connected with this acid are two of much importance, viz., malic acid, CHO,, and tartaric acid, CHO.. The former is found in many acid fruits and in the stalks of rhubarb, but is usually obtained from the unripe berries of the mountain-ash. It is a colorless .solid, dissolves readily in water and alcohol, and crystallizes with difficulty. The solutions of all the acids named have an agreeable acid taste, but become mouldy if long kept, and gradually undergo decomposition. Tartaric acid is found abundantly in the juices of many fruits. It is obtained by the decomposition of calcic tartrate with sulphuric acid. Its crystals, when pure, are colorless, transparent, permanent in the air, and dissolve readily in water or alcohol. It is extensively used by the calico-printer and dyer for the removal of mordants. Mixed with the bicarbonates of the alkalies, it forms the soda-powders of effervescing draughts. 550. Benzoic Acid, C,H,O,, obtained exclusively at one time from gum-benzoin, is now procured from hippuric acid, which occurs in the urine of herbivorous animals. 551. Salicylic Acid, CH, OH CO,H, is one of the derivatives of salicine, which is a neutral vegetable principle, discovered in 1830 in the bark of the willow, Salix, whence its name. The acid was early obtained from the flowers of the meadow-sweet (Spirea ulmaria), and it occurs in the oil of winter-green. It is now regarded with great interest, on account of its valuable qualities as an antiferment and antiseptic. As its practical value became known, the sources from which it had been obtained were found utterly inadequate to the increased demand; and the reconstructive power of the modern chemist sought for a compound, which might be split up, or reorganized in such a way as to yield the desired salicylic acid. The German chemists found this in phenol or carbolic acid, a substance long known for its valuable qualities as an antiferment. The agent selected to reconstruct the molecule of phenol was carbonic dioxide. The pure acid is obtained in minute acicular crystals, white, odorless, and nearly tasteless; insoluble in cold water, more soluble in hot water, and in still greater degree soluble in alcohol and ether. It melts at about 257° F. It is used in medicine and in surgical operations, where it is said to be more effective in smaller quantities than any other antiseptic, and to be devoid of all irritating action upon the living tissues. In cases of decomposition which cannot be reached by any other antiseptic, salicylic acid is claimed to be especially valuable. 552. Citric Acid, C.HO,, is found principally in fruits of the orange family, but is of frequent occurrence in gooseberries, currants, and other acid fruits. It may be readily procured from the juice of the lemon by the aid of chalk and sulphuric acid. It has a pleasant acid taste, is very soluble in water, and is used in medicine, calico-printing, and for effervescing draughts. Gallic acid, C,H,O,, occurs in sumach, acorns, tea, and many plants. It crystallizes in silky needles, is freely soluble in boiling water, and does not precipitate gelatine. Heated to about 215° C., gallic acid is decomposed into carbonic dioxide and pyrogallol, C.HO,. This acid is extensively used in photography. Both gallic acid and pyrogallol decompose the salts of silver, gold, and platinum; hence they are extensively employed in photography, and in the manufacture of hair-dyes. 553. Tannins (Tannic Acids).-There are several distinct compounds known under the name tannin, which resemble each other in character and possess an acid reaction. They are found extensively diffused throughout the vegetable kingdom, and are all distinguished by an astringent taste. The bark and leaves of most forest-trees, as well as of many fruit-trees, contain a large quantity of tannin; it is found in various roots, shrubs, and seeds, and is the astringent principle of tea and coffee. The most important of these compounds, obtained from gall-nuts, is generally known as gallotannic acid, C,,H2O17• It has an intensely astringent taste, reddens litmus-paper, and is very soluble in water. When a solution of gallotannic acid is mixed with a solution of a ferric compound, it produces a deep bluish-black precipitate, which is the basis of writing-ink. The gradual darkening of pale, 27 22 watery ink is due to the oxidation of the iron it contains. Tannins form insoluble compounds with starch, gelatine, and other organic bodies, the most remarkable being those with gelatine, which form the basis of leather. 554. Oxalic Acid, C,H,O,, is met with in the juice of the sorrel, rhubarb, and many plants, sometimes in the free state, but more frequently in the compound known as calcic oxalate. It is commonly prepared by the oxidation of sugar or starch with nitric acid: one part of sugar is dissolved in eight parts of nitric acid, and gently heated, when intense action ensues, with a copious disengagement of nitrous acid fumes. By evaporating the solution, oxalic acid may be obtained in large, transparent, and intensely sour crystals. Oxalic acid is poisonous, and its crystals resemble those of Epsom salts, for which it is sometimes mistaken. In cases of poisoning with it, chalk or magnesia, mixed in water, is the proper antidote. Oxalic acid is largely used in calico-printing; it is also employed as a delicate test for the presence of lime, with which it forms an insoluble salt. It removes ink and iron stains from linen by forming a soluble oxalate of iron, but the acid is so corrosive as to injure the fibre if not immediately removed by washing. 555. Alkaline Organic Salts.-The compounds of this group are derived from the organic acids by the substitution of a radicle of the Lithium group for the basic hydrogen of the acid. The most important salt of the acid series is hydro-potassic tartrate (cream of tartar), (HK), (CHO) O,. It is deposited in an impure state from wine constituting the tartar or argol of commerce. When purified by recrystallization, it forms a white crystalline powder, or larger crystals, soluble with difficulty in cold water, more readily in hot water, and possessing a pleasant sour taste. Among the salts of the neutral series, sodio-potassic tartrate (Rochelle salts), (NaK) (C,H,O,) 0, + 4 H,O, deserves special notice. It is obtained in beautiful large crystals, perfectly colorless when pure, of mild saline taste, by crystal |