ammonia, and 15 water; or probably of 3 primes carbonic acid, 2 ammonia, and 2 water; in all 14.76 for its equivalent. 2. But M. Gay-Lussac has shown, that when 100 volumes of ammoniacal gas are mixed with 50 of carbonic acid, the two gases precipitate in a solid salt, which must consist by weight of 564 acid +433 alkali, being in the ratio of a prime equivalent of each. 3. When the pungent sub-carbonate is exposed in powder to the air, it becomes scentless by the evaporation of a definite portion of its ammonia. It is then a compound of about 55 or 56 carbonic acid, 21.5 ammonia, and 22.5 water. It may be represented by 2 primes of acid, 1 of ammonia, and 2 of water, = 12. 4. Another compound, it has been supposed, may be prepared by passing carbonic acid through a solution of the sub-carbonate till it be saturated. This, however, may be supposed to yield the same product as the last salt. M. Gay-Lussac infers the neutral carbonate to consist of equal volumes of the two gases, though they will not directly combine in these proportions. This would give 18.1 to 46.5; the very proportions in the scentless salt. For 46.5: 18.1 :: 55:21.42.*

It is well known as a stimulant usually put into smelling-bottles, frequently with the addition of some odoriferous oil.

Fourcroy has found, that an ammoniacomagnesian carbonate is formed on some occasions. Thus, if carbonate of ammonia be decomposed by magnesia in the moist way, leaving these two substances in contact with each other in a bottle closely stopped, a complete decomposition will not take place, but a portion of this trisalt will be formed. The same will take place, if a solution of carbonate of magnesia in water, impregnated with carbonic acid, be precipitated by pure ammonia; or if ammoniaco-magnesian sulphate, nitrate, or muriate, be precipitated by carbonate of potash or of soda.

The properties of this triple salt are not yet known, but it crystallizes differently from the carbonate of either of its bases, and has its own laws of solubility and decomposition.

The carbonate of glucine has been examined by Vauquelin, and is, among the salts of that earth, that of which he has most accurately ascertained the proper ties. It is in a white, dull, clotty powder, never dry, but greasy, and soft to the feel. It is not sweet, like the other salts of glucine, but insipid. It is very light, insoluble in water, perfectly unalterable by the air, but very readily decomposed by fire. A saturated solution of carbonate of ammonia takes up a certain portion of this carbonate, and forms with it a triple salt. This property enabled Vauquelin to sepa

rate glucine from alumina, and was one of the means of his distinguishing that earth.

Carbonic acid does not appear to be much disposed to unite with argillaceous earth. Most clays, however, afford a small quantity of this acid by heat; and Fourcroy says, that the fat clays effervesce with acids. The snowy white substance resembling chalk, and known by the name of lac lune, is found to consist almost wholly of alumina saturated with carbonic acid. A saline substance, consisting of two six-sided pyramids joined at one common base, weighing five or six grains, and of a taste somewhat resembling alum, was produced by leaving an ounce phial of water impregnated with carbonic acid, and a redundancy of alumina, exposed to spontaneous evaporation for some months.

Vauquelin has found, that carbonate of zircone may be formed by evaporating muriate of zircone, redissolving it in water, and precipitating by the alkaline carbonates. He also adds, that it very readily combines so as to form a triple salt with either of the three alkaline carbonates.

* ACID (CASEIC). The name given by Proust to an acid found in cheese, to which he ascribes their flavour.

ACID (CETIC). The name given by M. Chevreul to a supposed peculiar principle of spermaceti, which he has lately found to be the substance he has called Margarine, combined with a fatty matter. *

ACID (CHLORIODIC). See ACID (HrDRIODIC).

ACID (CHLOROCARBONIC). See CHLORINE, and CHLOROCARBONOUS ACID.

ACID (CHLOROCYANIC). See ACID (PRUSsic).

ACID (CHROMIC). This acid has been examined principally by Vauquelin, who first discovered it, and by count Mussin Puschkin; yet we are better acquainted with it than with the metal that forms its basis. However, as the chromate of iron has lately been found in abundance in the department of Var, in France, and in some other places, we may expect its properties to be more amply investigated, and applied with advantage in the arts, as the chromates of lead and iron are of excellent use in painting and enamelling.

It was extracted from the red lead ore of Siberia, by treating this ore with carbonate of potash, and separating the alkali by means of a more powerful acid. In this state it is a red or orange-coloured powder, of a peculiar rough metallic taste, which is more sensible in it than in any other metallic acid. If this powder be exposed to the action of light and heat, it loses its acidity, and is converted into green oxide of chrome, giving out pure oxygen gas. The chromic acid is the first

that has been found to de-oxygenate itself easily by the action of heat, and afford oxygen gas by this simple operation. It appears that several of its properties are owing to the weak adhesion of a part at least of its oxygen. The green oxide of chrome cannot be brought back to the state of an acid, unless its oxygen be restored by treating it with some other acid.

The chromic acid is soluble in water, and crystallizes, by cooling and evaporation, in longish prisms of a ruby red. Its taste is acrid and styptic. Its specific gravity is not exactly known; but it always exceeds that of water. It powerfully reddens the tincture of turnsole.

Its action on combustible substances is little known. If it be strongly heated with charcoal, it grows black, and passes to the metallic state without melting.

Of the acids, the action of the muriatic on it is the most remarkable. If this be distilled with the chromic acid, by a gentle heat, it is readily converted into chlorine. It likewise imparts to it by mixture the property of dissolving gold; in which the chromic resembles the nitric acid. This is owing to the weak adhesion of its oxygen, and it is the only one of the metallic acids that possesses this property.

* The extraction of chromic acid from the French ore, is performed by igniting it with its own weight of nitre in a crucible. The residue is lixiviated with water, which being then filtered, contains the chromate of potash. On pouring into this a little nitric acid and muriate of barytes, an instantaneous precipitate of the chromate of barytes takes place. After having procured a certain quantity of this salt, it must be put in its moist state into a capsule, and dissolved in the smallest possible quantity of weak nitric acid. The barytes is to be then precipitated by very dilute sulphuric acid, taking care not to add an excess of it. When the liquid is found by trial to contain neither sulphuric acid nor barytes, it must be filtered. It now consists of water, with nitric and chromic acids. The whole is to be evaporated to dryness, conducting the heat at the end, so as not to endanger the decomposition of the chromic acid, which will remain in the capsule under the form of a reddish matter. It must be kept in a glass phial well corked.

Chromic acid, heated with a powerful acid, becomes chromic oxide; while the latter, heated with the hydrate of an alkali, becomes chromic acid. As the solution of the oxide is green. and that of the acid yellow, these transmutations become very remarkable to the eye. From Berzelius's experiments on the combinations of the chromic acid with barytes, and oxide of lead, its prime equivalent seems to be 6.5;

consisting of 3.5 chromium, and 3.0 охуgen.* SEE CHROMIUM.

It readily unites with alkalis, and is the only acid that has the property of colouring its salts, whence the name of chromic has been given it. If two parts of the red lead ore of Siberia in fine powder be boiled with one of an alkali saturated with carbonic acid, in forty parts of water, a carbonate of lead will be precipitated, and the chromate remain dissolved. The solutions are of a lemon colour, and afford crystals of a somewhat deeper hue. Those of chromate of ammonia are in yellow laminæ, having the metallic lustre of gold.

The chromate of barytes is very little soluble, and that of lime still less. They are both of a pale yellow, and when heated give out oxygen gas, as do the alkaline chromates.

If the chromic acid be mixed with filings of tin and the muriatic acid, it becomes at first yellowish brown, and afterwards assumes a bluish green colour, which preserves the same shade after desiccation. Ether alone gives it the same dark colour. With a solution of nitrate of mercury, it gives a precipitate of a dark cinnabar coIour. With a solution of nitrate of silver it gives a precipitate, which, the moment it is formed, appears of a beautiful carmine colour, but becomes purple by exposure to the light. This combination, exposed to the heat of the blow-pipe, melts before the charcoal is inflamed, and assumes a blackish and metallic appearance. If it be then pulverized, the powder is still pur-. ple; but after the blue flame of the lamp is brought into contact with this powder, it assumes a green colour, and the silver appears in globules disseminated through its substance.

With nitrate of copper it gives a chesnut red precipitate. With the solution of sulphate of zinc, muriate of bismuth, muriate of antimony, nitrate of nickel, and muriate of platina, it produces yellowish precipitates, when the solutions do not contain an excess of acid. With muriate of gold it produces a greenish precipitate.

When melted with borax, or glass, or acid of phosphorus, it communicates to it a beautiful emerald green colour.

If paper be impregnated with it, and exposed to the sun a few days, it acquires a green colour, which remains permanent in the dark.

A slip of iron, or tin, put into its solution, imparts to it the same colour. The aqueous solution of tannin produces flocculent precipitate of brown fawn

a

colour.

a

Sulphuric acid, when cold, produces no effect on it; but when warm it makes it assume a bluish green colour.

ACID (CITRIC). The juice of lemons

or limes, has all the characters of an acid of considerable strength; but on account of the mucilaginous matter with which it is mixed, it is very soon altered by spontaneous decomposition. Various methods have been contrived to prevent this effect from taking place, in order that this wholesome and agreeable acid might be preserved for use in long voyages, or other domestic occasions. The juice may be kept in bottles under a thin stratum of oil, which indeed prevents, or greatly retards, its total decomposition; though the original fresh taste soon gives place to one which is much less grateful. In the East Indies it is evaporated to the consistence of a thick extract. If this operation be carefully performed by a very gentle heat, it is found to be very effectual. When the juice is thus heated, the mucilage thickens, and separates in the form of flocks, part of which subsides, and part rises to the surface these must be taken out. The vapours which arise are not acid. If the evaporation be not carried so far as to deprive the liquid of its fluidity, it may be long preserved in well closed bottles; in which, after some weeks' standing, a farther portion of mucilage is separated, without any perceptible change in the acid.

Of all the methods for preserving lemon-juice, that of concentrating it by frost appears to be the best, though in the warmer climates it cannot conveniently be practised. Lemon-juice, exposed to the air, in a temperature between 50° and 60°, deposites s in in a a few hours a white semi

transparent mucilaginous matter, which leaves the fluid, after decantation and filtration, much less alterable than before. This mucilage is not of a gummy nature, but resembles the gluten of wheat in its properties: it is not soluble in water when dried. More mucilage is separated from lemon-juice by standing in closed vessels. If this depurated lemon-juice be exposed to a degree of cold of about seven or eight degrees below the freezing point, the aqueous part will freeze, and the ice may be taken away as it forms; and if the process be continued until the ice begins to exhibit signs of acidity, the remaining acid will be found to be reduced to about one-eighth of its original quantity, at the same time that its acidity will be eight times as intense, as is proved by its requiring eight times the quantity of alkali to saturate an equal portion of it. This concentrated acid may be kept for use, or, if preferred, it may be made into a dry lemonade, by adding six times its weight of fine loaf sugar in powder.

The above processes may be used when the acid of lemons is wanted for domestic purposes, because they leave it in posses

sion of the oils, or other principles, on which its flavour peculiarly depends; but in chemical researches, where the acid itself is required to be had in the utmost purity, a more elaborate process must be used. Boiling lemon-juice is to be saturated with powdered chalk, the weight of which is to be noted, and the powder must be stirred up from the bottom, or the vessel shaken from time to time. The neutral saline compound is scarcely more soluble in water than selenite; it therefore falls to the bottom, while the mucilage remains suspended in the watery fluid, which must be decanted off'; the remaining precipitate must then be washed with warm water until it comes off clear. To the powder thus edulcorated, a quantity of sulphuric acid, equal the chalk in weight, and diluted with ten parts of water, must be added, and the mixture boiled a few minutes. The sulphuric acid combines with the earth, and forms sulphate of lime, which remains behind when the cold liquor is filtered, while the disengaged acid of lemons remains dissolved in the fluid. This last must be evaporated to the consistence of a thin sirup, which yields the pure citric acid in little needlelike crystals. It is necessary that the sulphuric acid should be rather in excess, because the presence of a small quantity of lime will prevent the crystallization. This excess is allowed for above.

M. Dize, a skilful apothecary in Paris, who has repeated this process of Scheele on a very extensive scale, asserts, that an excess of sulphuric acid is necessary, not only to obtain the citric acid pure, but to destroy the whole of the mucilage, part of which would otherwise remain, and occasion its spoiling. It is not certain, however, but the sulphuric acid may act on the citric itself, and by decomposing it, produce the charcoal that M. Dize ascribes to the decomposition of mucilage; and if so, the smaller the excess of sulphuric acid the better. He also adds, that to have it perfectly pure it must be repeatedly crystallized, and thus it forms very large and accurately defined crystals in rhomboidal prisms, the sides of which are inclined in angles of 60° and 120°, terminated at each end by tetraedral summits, which intercept the solid angles. These, however, will not be obtained when operating on small quantities.

Its taste is extremely sharp, so as to appear caustic. Distilled in a retort, part rises without being decomposed; it appears to give out a portion of vinegar; it then evolves carbonic acid gas, and a little carburetted hydrogen; and a light coal remains. It is among the vegetable acids the one which most powerfully resists decomposition by fire.

In a dry and warm air it seems to effloresce; but it absorbs moisture when the air is damp, and at length loses its crystalline form. A hundred parts of this acid are soluble in seventy-five of water at 60°, according to Vauquelin. Though it is less alterable than most other solutions of vegetable acids, it will undergo decomposition when long kept. Fourcroy thinks it probable that it is converted into acetic acid before its final decomposition.

It is not altered by any combustible substance; charcoal alone appears to be capable of whitening it. The most powerful acids decompose it less easily than they do other vegetable acids; but the sulphuric evidently converts it into acetic acid. The nitric acid likewise, according to Fourcroy and Vauquelin, if employed in large quantity, and heated on it a long time, converts the greater part of it into acetic acid, and a small portion into oxalic. Scheele indeed could not effect this; but Westrumb supposes that it was owing to his having used too much nitric acid; for on treating 60 grains of citric acid with 200 of nitric he obtained 30 grains of oxalic acid; with 300 grains of nitric acid he got 15; and with 600 grains no vestige of oxalic acid appeared

If a solution of barytes be added gradually to a solution of citric acid, a flocculent precipitate is formed, soluble by agitation, till the whole of the acid is saturated. This salt at first falls down in powder, and then collects in silky silky tufts, tufts, and a kind of very beautiful and shining silvery bushes. It requires a large quantity of water to dissolve it.

The citrate of lime has been mentioned already in treating of the mode of purifying the acid.

The citrate of potash is very soluble and deliquescent.

The citrate of soda has a dull saline taste; dissolves in less than twice its weight of water; crystallizes in six-sided prisms with flat summits; effloresces slightly, but does not fall to powder; boils up, swells, and is reduced to a coal on the fire. Lime-water decomposes it, but does not render the solution turbid, notwithstanding the little solubility of citrate of lime.

Citrate of ammonia is very soluble; does not crystallize unless its solution be greatly concentrated; and forms elongated prisms.

Citrate of magnesia does not crystallize. When its solution had been boiled down, and it had stood some days, on being slightly shaken it fixed in one white opaque mass, which remained soft, separating from the sides of the vessel, contracting its dimensions, and rising in the middle like a kind of mushroom.

Its combination with the other earths has not been much examined; and its action upon metals has been little studied. Scheele however found, that it did not precipitate the nitric solutions of metals, as the malic acid does.

All the citrates are decomposed by the powerful acids, which do not form a precipitate with them, as with the oxalates and tartrates. The oxalic and tartaric acids decompose them, and form crystallized or insoluble precipitates in their solutions. All afford traces of acetic acid, or a product of the same nature, on being exposed to distillation: this character exists particularly in the metallic citrates. Placed on burning coals they melt, swell up, emit an empyreumatic smell of acetic acid, and leave a light coal. All of them, if dissolved in water, and left to stand for a time, undergo decomposition, deposite a flocculent mucus which grows black, and leave their bases combined with carbonic acid, one of the products of the decomposition. Before they are completely decomposed, they appear to pass to the state of acetates.

The affinities of the citric acid are arranged by Vauquelin in the following order: barytes, lime, potash, soda, strontian, magnesia, ammonia, alumina. Those for zircone, glucine, and the metallic oxides, are not ascertained.

The citric acid is found in many fruits united with the malic acid; which see for the process of separating them in this

Citric acid being more costly than tartaric, may be occasionally adulterated with it. This fraud is discovered, by adding slowly to the acid dissolved in water a solution of sub-carbonate of potash, which will give a white pulverulent precipitate of tartar, if the citric be contaminated with the tartaric acid. When one part of the citric acid is dissolved in 19 of water, the solution may be used as a substitute for lemon-juice. If before solution the crys tals be triturated with a little sugar and a few drops of the oil of lemons, the resem

blance to the native juice will be complete. It is an antidote against sea scurvy; but the admixture of mucilage and other vegetable matter in the recent fruit of the lemon, has been supposed to render it preferable to the pure acid of the chemist.*

ACID (CHLORIC). See ACID (MURIATIC.) * ACID (COLUMBIC). The experiments of Mr. Hatchett have proved, that a peculiar mineral from Massachusetts, deposited in the British Museum, consisted of one part of oxide of iron, and somewhat more than three parts of a white coloured substance, possessing the properties of an acid. Its basis was metallic. Hence he named this Columbium, and the acid the Columbic. Dr. Wollaston, by very exact analytical comparisons, proved, that the acid of Mr. Hatchett, was the oxide of the metal lately discovered in Sweden by Mr. Ekeberg, in the mineral yttrotantalite, and thence called tantalum. Dr. Wollaston's method of separating the acid from the mineral is peculiarly elegant. One part of tantalite, five parts of carbonate of potash, and two parts of borax, are fused together in a platina crucible. The mass, after being softened in water, is acted on by muriatic acid. The iron and manganese dissolve, while the columbic acid remains at the bottom. It is in the form of a white powder, which is insoluble in nitric and sulphuric acids, but partially in muriatic. It forms with barytes an insoluble salt, of which the proportions, according to Berzelius, are 24.4 acid, and 9.75 barytes. By oxidizing a portion of the revived tantalum or columbium, Berzelius infers the composition of the acid to be 100 metal and 5.485 oxygen.

ACID (CYANIC). See ACID (PRUSSIC).

ACID (FLUORIC). The fusible spar which is generally distinguished by the name of Derbyshire spar, consists of calcareous earth in combination with the acid at present under our consideration. If the pure fluor, or spar, be placed in a retort of lead or silver, with a receiver of the same metal adapted, and its weight of sulphuric acid be then poured upon it, the fluoric acid will be disengaged by the application of a moderate heat. This acid gas readily combines with water; for which purpose it is necessary that the receiver should previously be half filled with that fluid.

* If the receiver be cooled with ice, and no water put in it, then the condensed acid is an intensely active liquid, first procured by M. Gay-Lussac. The best account of it, however, has been given by Sir H. Davy. It has the appearance of sulphuric acid, but is much more volatile, and sends off white fumes when exposed to air. Its specific gravity is only 1.0609. It must be examined with great caution, for when

applied to the skin it instantly disorganizes it, and produces very painful wounds. When potassium is introduced into it, it acts with intense energy, and produces hydrogen gas and a neutral salt; when lime is made to act upon it, there is a violent heat excited, water is formed, and the same substance as fluor spar is produced. With water in a certain proportion, its density increases to 1.25. When it is dropped into water, a hissing noise is produced with much heat, and an acid fluid not disagreeable to the taste is formed if the water be in sufficient quantity. It instantly corrodes and dissolves glass.

It appears extremely probable, from all the facts known respecting the fluoric combinations, that fluor spar contains a peculiar acid matter; and that this acid matter is united to lime in the spar, seems evident from the circumstance, that gypsum or sulphate of lime is the residum of the distillation of fluor spar and sulphuric acid. The results of experiments on fluor spar have been differently stated by chemists. Sir H. Davy states, that 100 fluor spar yield 175.2 sulphate of lime; whence we deduce the prime equivalent of fluoric acid to be 1.3260, to lime, 3.56, and oxygen 1.00. From fluate of potash the equivalent comes out for the acid, = 1.2495, potash being reckoned 5.95. Berzelius in his last series of experiments gives from fluate of lime, 1.374 for the equivalent of fluoric acid. The dense fluid obtained in silver vessels, may be regarded as hydrofluoric acid; and, supposing all the water in oil of vitriol transferred to it, would consist of 1.326 or 1.374 acid, + 1.125 water; which is a prime of each.

Dr. Thomson, in his System of Chemistry fifth edition, vol. i. p. 203, deduces the equivalent of fluoric acid from the decomposition of fluate of lime by sulphuric acid, to be 1.0095; and, from the lowness of this number, he afterwards endeavours to prove that fluoric acid cannot be a compound of oxygen with a base. Now taking his own data of 100 parts of fluor spar yielding, according to Sir H. Davy's latest experiments, 175.2 sulphate of lime; and admitting that these contain 73.582 of lime; leaving consequently 26.418 for the proportion of acid in 100 of fluor spar, we shall find 1.3015 to be the equivalent or atom of fluoric acid. For 73.582: 3.625: 26.418: 1.3015, taking his own number 3.625 for the atom of lime. Hence the whole difficulties stated by him in the following passage, page 206, disappear :-“ If we suppose fluate of lime to be a compound of fluoric acid and lime, its composition will be, Fluoric acid, 1.0095. 3.625

Lime.

From this we see that the weight of an integrant particle of fluoric acid must be