its composition, and that it is in the superabundance of this combustible principle its difference from the other vegetable acids consists. Its solubility in the power ful acids, and its subsequent separation, indicate that its principles are not easily separable from each other. Attempts have been made to decompose it by repeated abstraction of nitric acid; the nitric acid rises first, scarcely altered except toward the end of the process, when nitrous gas comes over; and the acid of benzoin is afterwards sublimed with little alteration. By repeating the process, however, it is said to become more fixed, and at length to afford a few drops of an acid resembling the oxalic in its properties. * Berzelius, from the benzoate of lead, deduces the weight of the prime equivalent of benzoic acid to be 14.893; and it consists per cent of 5.16 hydrogen, 74.41 carbon, and 20.43 oxygen. The benzoates are all decomposable by heat, which, when it is slowly applied, first separates a portion of the acid in a vapour, that condenses in crystals. The soluble benzoates are decomposed by the powerful acids, which separate their acid in a crystalline form. The benzoate of ammonia has been proposed by Berzelius as a reagent for precipitating red oxide of iron from perfectly neutral solutions. According to my experiments, 21.3 of am imonia take 15.7 of crystallized benzoic acid for neutralization.* The benzoic acid is occasionally used in medicine, but not so much as formerly; and enters into the composition of the camphorated tincture of opium of the London col college, heretofore called paregoric elixir. * ACID (BOLETIC). An acid extracted from the expressed juice of the boletus pseudo-igniarius by M. Braconnot. This juice concentrated to a sirup by a very gentle heat, was acted on by strong alcohol. What remained was dissolved in water. When nitrate of lead was dropped into this solution, a white precipitate fell, which, after being well washed with water, was decomposed by a current of sulphuretted hydrogen gas. Two different acids were found in the liquid after filtration and evaporation. One in permanent crystals was BOLETIC acid; the other was a small proportion of phosphoric acid. The former was purified by solution in alcohol, and subsequent evaporation. It consists of irregular four-sided prisms, of a white colour, and permanent in the air. Its taste resembles cream of tartar; at the temperature of 68° it dissolves in 180 times its weight of water, and in 45 of alcohol. Vegetable blues are reddened by it. Red oxide of iron, and the oxides of silver and mercury, are precipitated by it from their solutions in nitric acid; but lime and barytes waters are not affected. It sublimes when heated, in white vapours, and is condensed in a white powder. Ann. de Chimie, lxxx.* ACID (BORACIC). The salt composed of this acid and soda, had long been used both in medicine and the arts under the name of borax, when Homberg first obtained the acid separate in 1702, by distilling a mixture of borax and sulphate of iron. He supposed, however, that it was a product of the latter; and gave it the name of volatile narcotic salt of vitriol, or sedative salt. Lemery the younger soon after discovered, that it could be obtained from borax equally by means of the nitric or muriatic acid; Geoffroy detected soda in borax; and at length Baron proved by a number of experiments, that borax is a compound of soda and a peculiar acid. Cadet has disputed this; but he has merely shown, that the borax of the shops is frequently contaminated with copper; and Struve and Exchaquet have endeavoured to prove that the boracic and phosphoric acids are the same; yet their experiments only show, that they resemble each other in certain respects, not in all. To procure the acid, dissolve borax in hot water, and filter the solution; then add sulphuric acid by little and little, till the liquid has a sensibly acid taste. Lay it aside to cool, and a great number of small shining laminated crystals will form. These are the boracic acid. They are to be washed with cold water, and drained upon brown paper. Boracic acid thus procured is in the form of thin irregular hexagonal scales, of a silvery whiteness, having some resemblance to spermaceti, and the same kind of greasy feel. It has a sourish taste at first, then makes a bitterish cooling -impression, and at last leaves an agreeable sweetness. Pressed between the teeth, it is not brittle but ductile. It has no smell; but, when sulphuric acid is poured on it, a transient odour of musk is produced. Its specific gravity in the form of scales is 1.479; after it has been fused, 1.803. It is not altered by light. Exposed to the fire it swells up, from losing its water of crystallization, and in this state is called calcined boracic acid. It melts a little before it is red-hot, without perceptibly losing any water, but it does not flow freely till it is red, and then less than the borate of soda. After this fusion it is a hard transparent glass, becoming a little opaque on exposure to the air, without abstracting moisture from it, and unaltered in its properties, for on being dissolved in boiling water it crystallizes as before. This glass is used in the composition of false gems. Boiling water scarcely dissolves one fiftieth part, and cold water much less. When this solution is distilled in close vessels, part of the acid rises with the water, and crystallizes in the receiver. It is more soluble in alcohol, and alcohol containing it burns with a green flame, as does paper dipped in a solution of boracic acid. Neither oxygen gas, nor the simple com. bustibles, nor the common metals, produce any change upon boracic acid, as far as is at present known. If mixed with finely powdered charcoal, it is nevertheless capable of vitrification; and with soot it melts into a black bitumen-like mass, which however is soluble in water, and cannot easily be burned to ashes, but sublimes in part. With the assistance of a distilling heat it dissolves in oils, especially mineral oils; and with these it yields fluid and solid products, which impart a green colour to spirit of wine. When rubbed with phosphorus it does not prevent its inflammation, but an earthy yellow matter is left behind. It is hardly capable of oxidizing or dissolving any of the metals except iron and zinc, and perhaps copper; but it combines with most of the metallic oxides, as it does with the alkalis, and probably with all the earths, though the greater part of its combinations have hitherto been little examined. It is of great use in analyzing stones that contain a fixed alkali. * Crystallized boracic acid is a compound of 57 parts of acid and 43 of water. The honour of discovering the radical of boracic acid, is divided between Sir H. Davy and M. M. Gay-Lussac and Thenard. The first, on applying his powerful voltaic battery to it, obtained a chocolate-coloured body in small quantity; but the two latter chemists, by acting on it with potassium in equal quantities, at a low red heat, formed boron and subborate of potash. For a small experiment a glass tube will serve, but on a greater scale a copper tube is to be preferred. The potassium and boracic acid, perfectly dry, should be intimately mixed before exposing them to heat. On withdrawing the tube from the fire, allowing it to cool, and removing the cork which loosely closed its mouth, we then pour successive portions of water into it, till we detach or dissolve the whole matter. The water ought to be heated each time. The whole collected liquids are allowed to settle; when, after washing the precipitate till the liquid ceases to affect sirup of violets, we dry the boron in a capsule, and then put it into a phial out of contact of air. Boron is solid, tasteless, inodorous, and of a greenish brown colour. Its specific gravity is somewhat greater than water. The prime equivalent of boracic acid has been inferred from [4] VOLK the borate of ammonia, to be about 2.7 or 2.8; oxygen being 1.0; and it probably consists of 2.0 of oxygen + 0.8 of boron. But by M. M. Gay-Lussac and Thenard, the proportions would be 2 of boron to 1 of oxygen.* The boracic acid has a more powerful attraction for lime, than for any other of the bases, though it does not readily form borate of lime by adding a solution of it to lime-water, or decomposing by lime-water the soluble alkaline borates. In either case an insipid white powder, nearly insoluble, which is the borate of lime, is however precipitated. The borate of barytes is likewise an insoluble, tasteless, white powder. Bergmann has observed, that magnesia, thrown by little and little into a solution of boracic acid, dissolved slowly, and the liquor on evaporation afforded granulated crystals without any regular form: that these crystals were fusible in the fire without being decomposed; but that alcohol was sufficient to separate the boracic acid from the magnesia. If however some of the soluble magnesian salts be decomposed by alkaline borates in a state of solution, an insipid and insoluble borate of magnesia is thrown down. It is probable, therefore, that Bergmann's salt was a borate of magnesia dissolved in an excess of boracic acid; which acid being taken up by the alcohol, the true borate of magnesia was precipitated in a white powder, and mistaken by him for magnesia. One of the best known combinations of this acid is the native magnesio-calcareous borate of Kalkberg, near Lunenburg: the wurfelstein of the Germans, cubic quartz of various mineralogists, and boracite of Kirwan. It is of a grayish white colour, sometimes passing into the greenish white, or purplish. Its figure is that of a cube, incomplete on its twelve edges, and at four of its solid angles; the complete and incomplete angles being diametrically opposite to each other. The surfaces generally appear corroded. It strikes fire with steel, and scratches glass. Its specific gravity is 2.566, as determined by M. Westrumb, who found it to be composed of boracic acid 0.68, magnesia 0.1305, lime 0.11; with alumina 0.01, silex 0.02, and oxide of iron 0.0075, all of which he considers as casual. Its most remarkable property, discovered by Haiy, is, that like the tourmalin it becomes electric by heat, though little so by friction; and it has four electric poles, the perfect angles always exhibiting negative electricity, and the truncated angles positive. Since the component parts of this native salt have been known, attempts have been made to imitate it by art; but no chemist has been able, by mixing lime, magnesia, and boracic acid, to produce any thing but a pulverulent salt, incapable of being dissolved, or exhibited in the crystallized form, and with the hardness of the borate of Kalkberg. acid, and then separating the two salts but it is obviously more eligible, to saturate the excess of soda with an additional portion of the horacic acid itself. Borate of ammonia forms in small rhomboidal crystals, easily decomposed by fire; or in scales, of a pungent urinous taste, which lose the crystalline form, and grow brown on exposure to the air. It is very difficult to combine the boracic acid with alumina, at least in the direct way. It has been recommended, for this purpose, to add a solution of borax to a solution of sulphate of alumina; but for this process the neutral borate of soda is preferable, since, if borax be employed, the soda that is in excess may throw down a precipitate of alumina, which might be mistaken for an earthy borate. It has lately been denied, however, that this compound is really a triple salt. Vauquelin, examining this substance with Mr. Smith, who had a considerable quantity, found the powder to effervesce with acids; and therefore concluded the lime to be no essential part of the compound. They at tempted, by using weak acids much diluted, to separate the carbonate from the borate; but they did not succeed, because the acid attacked the borate likewise, though feebly. M. Stromager having afterwards supplied Vauquelin with some transparent crystals, which did not effervesce with acids, he mixed this powder with muriatic acid, and, when the solution was effected by means of heat, evaporated to dryness to expel the excess of acid. By solution in a small quantity of cold distilled water, he separated most of the boracic acid; and, having diluted the solution, added a certain quantity of oxalate of ammonia, but no sign of the existence of lime appeared. To ascertain that the precipitation of the lime was not prevented by the presence of the small quantity of boracic acid, he mixed with the solution a very small portion of mu-chiaio, and Castellonuovo in Tuscany, in riate of lime, and a cloudiness immediately ensued through the whole. Hence he infers, that the opacity of the magnesian borate is occasioned by carbonate of lime interposed between its particles, and that the borate in transparent crystals contains none. The borate of potash is but little known, though it is said to be capable of supplying the place of that of soda in the arts; but more direct experiments are required to establish this effect. Like that, it is capable of existing in two states, neutral and with excess of base, but it is not so crystallizable, and assumes the form of parallelopipeds. With soda the boracic acid forms two different salts. One, in which the alkali is more than triple the quantity necessary to saturate the acid, is of considerable use in the arts, and has long been known by the name of borax; under which its his tory and an account of its properties will be given. The other is a neutral salt, not changing the sirup of violets green like the borate with excess of base; differing from it in taste and solubility; crystallizing neither so readily, nor in the same manner; not efflorescent like it; but like it fusible into a glass, and capable of being employed for the same purposes. This salt may be formed by saturating the su perabundant soda in borax with some other The boracic acid unites with silex by fusion, and forms with it a solid and permanent vitreous compound. This borate of silex, however, is neither sapid, nor soluble, nor perceptibly alterable in the air; and cannot be formed without the assistance of a violent heat. In the same manner triple compounds may be formed with silex and borates already saturated with other bases. The boracic acid has been found in a disengaged state in several lakes of hot mineral waters near Monte Rotondo, Ber the proportion of nearly nine grains in a hundred of water, by M. Hoeffer. M. Mascagni also found it adhering to schistus, on the borders of lakes, of an obscure white, yellow, or greenish colour, and crystallized in the form of needles. He has likewise found it in combination with ammonia. ACID (CAMPHORIC). M. Kosegarten found some years ago, that an acid with peculiar properties was obtained, by distilling nitric acid eight times following from camphor. Bouillon Lagrange has since repeated his experiments, and the following is the account he gives of its preparation and properties. One part of camphor being introduced into a glass retort, four parts of nitric acid of the strength of 36 degrees are to be poured on it, a receiver adapted to the retort, and all the joints well luted. The retort is then to be placed on a sand-bath, and gradually heated. During the process a considerable quantity of nitrous gas, and of carbonic acid gas, is evolved; and part of the camphor is volatilized, while another part seizes the oxygen of the nitric acid. When no more vapours are extricated, the vessels are to be separated, and the sublimed camphor added to the acid that remains in the retort. A like quantity of nitric acid is again to be poured on this, and the distillation repeat ed. This operation must be reiterated till the camphor is completely acidified. Twenty parts of nitric acid at 36 are sufficient to acidify one of camphor. When the whole of the camphor is acidified, it crystallizes in the remaining liquor. The whole is then to be poured out upon a filter, and washed with distilled water, to carry off the nitric acid it may have retained. The most certain indication of the acidification of the camphor is its crystallizing on the cooling of the liquor remaining in the retort. To purify this acid it must be dissolved in hot distilled water, and the solution, after being filtered, evaporated nearly to half, or till a slight pellicle forms; when the camphoric acid will be obtained in crystals on cooling. This experiment being too long long to be exhibited by the chemical lecturer, its place may be supplied by the following. A jar is to be filled over mercury with oxygen gas from the chlorate of potash, and a little water passed into it. On the other hand, a bit of camphor and an atom of phosphorus are to be placed in a little cupel; and then one end of a curved tube is to be conveyed under the jar, and the other end under a jar filled with water in the pneumato-chemical apparatus. The apparatus being thus arranged, the phosphorus is to be kindled by means of a red hot iron. The phosphorus inflames, and afterwards the camphor. The flame produced by the camphor is very vivid; much heat is given out; and the jar is lined with a black substance, which gradually falls down, and covers the water standing on the quicksilver in the jar. This is oxide of carbon. At the same time a gas is collected, that has all the characters of carbonic acid. The water contained in the jar is very fragrant, and contains camphoric acid in solution. The camphoric acid has a slightly acid, bitter taste, and reddens infusion of litmus. It crystallizes; and the crystals upon the whole resemble those of muriate of ammonia. (Kosegarten says they are parallelopipeds of a snowy whiteness.) It effloresces on exposure to the atmosphere; is not very soluble in cold water; when placed on burning coals, gives out a thick aromatic smoke, and is entirely dissipated; and with a gentle heat melts, and is sublimed. The mineral acids dissolve it entirely. It decomposes the sulphate and muriate of iron. The fixed and volatile oils dissolve it. It is likewise soluble in alcohol, and is not precipitated from it by water; a property that distinguishes it from the benzoic acid. It unites easily with the earths and alkalis. To prepare the camphorates of lime, magnesia and alumina, these earths must be diffused in water, and crystallized camphos ric acid added. The mixture must then be boiled, filtered while hot, and the solution concentrated by evaporation. The camphorate of barytes is prepared by dissolving the pure earth in water, and then adding crystallized camphoric acid. Those of potash, soda, and ammonia, should be prepared with their carbonates dissolved in water: these solutions are to be saturated with crystallized camphoric acid, heated, filtered, evaporated, and cooled, by which means the camphorates will be obtained. If the camphoric acid be very pure, they have no smell; if it be not, they have always a slight smell of camphor. The camphorates of alumina and barytes leave a little acidity on the tongue; the rest have a slightly bitterish taste. They are all decomposed by heat; the acid being separated and sublimed, and the base remaining pure; that of ammonia excepted, which is entirely volatilized. If they be exposed to the blow-pipe, the acid burns with a blue flame: that of ammonia gives first a blue flame; but toward the end it becomes red. The camphorates of lime and magnesia are little soluble, the others dissolve more easily. The mineral acids decompose them all. The alkalis and earths act in the order of their affinity for the camphoric acid; which is, lime, potash, soda, barytes, ammonia, alumina, magnesia. Several metallic solutions, and several neutral salts, decompose the camphorates; such as the nitrate of barytes, most of the calcareous salts, &c. The camphorates of lime, magnesia, and barytes, part with their acid to alcohol.-Lagrange's Manuel d'un Cours de Chimie. ACID (CARBONIC). This acid, being a compound of carbon and oxygen, may be formed by burning charcoal; but as it exists in great abundance ready formed, it is not necessary to have recourse to this expedient. All that is necessary is to pour sulphuric acid, diluted with five or six times its weight of water, on common chalk, which is a compound of carbonic acid and lime. An effervescence ensues; carbonic acid is evolved in the state of gas, and may be received in the usual manner. As the rapid progress of chemistry during the latter part of the 18th century, was in a great measure owing to the discovery of this acid, it may be worth while to trace the history of it somewhat particularly. Paracelsus and Van Helmont were acquainted with the fact, that air is extricated from solid bodies during certain processes; and the latter gave to air thus : produced the name of gas. Boyle called these kinds of air artificial airs, and suspected that they might be different from the air of the atmosphere. Hales ascertained the quantity of air that could be extricated from a great variety of bodies, and showed that it formed an essential part of their composition. Dr. Black proved, that the substances then called lime, magnesia, and alkalis, were compounds, consisting of a peculiar species of air, and pure lime, magnesia, and alkali. To this species of air he gave the name of fixed air, because it existed in these bodies in a fixed state. This air or gas was afterwards investigated, and a great number of its properties ascertained, by Dr. Priestley. From these properties Mr. Keir first concluded that it was an acid; and this opinion was soon confirmed by the experiments of Bergmann, Fontana, and others. Dr. Priestley at first suspected that this acid entered as an element into the composition of atmospherical air; and Bergmann, adopting the same opinion, gave it the name of aerial acid. Mr. Bewley called it mephitic acid, because it could not be respired without occasioning death; and this name was also adopted by Morveau. Mr. Keir called it calcareous acid; and at last M. Lavoisier, after discovering its composition, gave it the name of carbonic acid gas. The opinions of chemists concerning the composition of carbonic acid have undergone as many revolutions as its name. Dr. Priestley and Bergmann seem at first to have considered it as an element; and several celebrated chemists maintained that it was the acidifying principle. Afterwards it was discovered to be a compound, and that oxygen gas was one of its component parts. Upon this discovery the prevalent opinion of chemists was, that it consisted of oxygen and phlogiston; and when hydrogen and phlogiston came, according to Mr. Kirwan's theory, to signify the same thing, it was of course maintained that carbonic acid was composed of oxygen and hydrogen: and though M. Lavoisier demonstrated that it was formed by the combination of carbon and oxygen, this did not prevent the old theory from being maintained; because carbon was itself considered as a compound, into which a very great quantity of hydrogen entered. But after M. Lavoisier had demonstrated, that the weight of the carbonic acid produced was precisely equal to the charcoal and oxygen employed; after Mr. Cavendish had discovered. that oxygen and hydrogen when combined did not form carbonic acid, but water, it was no longer possible to doubt that this acid was composed of carbon and oxygen. According all farther dispute about it is at an end. Ty, If any thing were still wanting, to put this conclusion beyond the reach of doubt, it was to decompose carbonic acid, and thus to exhibit its component parts by analysis as well as synthesis. This has been actually done by Mr. Tennant. Into a tube of glass he introduced a bit of phosphorus and some carbonate of lime. He then sealed the tube hermetically, and applied heat. Phosphate of lime was formed, and a quantity of charcoal deposited. Now phosphate of lime is composed of phosphoric acid and lime, and phosphoric acid is composed of phosphorus and oxygen. The substances introduced into the tube were phosphorus, lime, and carbonic acid, and the substances found in it were phosphorus, lime, oxygen, and charcoal. The carbonic acid, therefore, must have been decomposed, and it must have consisted of oxygen and charcoal.This experiment was repeated by Doctor Pearson, who ascertained that the weight of the oxygen and charcoal together was equal to that of the carbonic acid which had been introduced; and in order to show that it was the carbonic acid which had been decomposed, he introduced pure lime and phosphorus; and, instead of phosphate of lime and carbon, he got nothing but phosphuret of lime. These experiments were also confirmed by Fourcroy, Vauquelin, Sylvestre, and Brongniart. Count Mussin-Puschkin too boiled a solution of carbonate of potash on purified phosphorus, and obtained charcoal. This he considered as an instance of the decomposition of carbonic acid, and as a confirmation of the experiments above related. Carbonic acid abounds in great quantities in nature, and appears to be produced in a variety of circumstances. It composesos of the weight of limestone, marble, calcareous spar, and other natural specimens of calcareous earth, from which it may be extricated either by the simple application of heat, or by the superior affinity of some other acid; most acids having a stronger action on bodies than this. This last process does not require heat, because fixed air is strongly disposed to assume the elastic state. Water, under the common pressure of the atmosphere, and at a low temperature, absorbs somewhat more than its bulk of fixed air, and then constitutes a weak acid. If the pressure be greater, the absorption is augmented. It is to be observed, likewise, that more gas than water will absorb, should be present. Heated water absorbs less; and if water, impregnated with this acid, be exposed on a brisk fire, the rapid escape of the aërial bubbles affords an appearance as if the water were at the point of boiling, when the heat is not greater than the hand can bear. Congelation se |