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of ammonia, a solution and precipitate of a beautiful gold-yellow colour; and a most brilliant iridescent pellicle, in which green and yellow predominate, forms on the sur face of the solution. Dr. Prout conceives the salts to be anhydrous, or void of water, and composed of two atoms of acid and one of base. The purpuric acid and its compounds probably constitute the bases of many animal and vegetable colours. The well known pink sediment which generally appears in the urine of those Jabouring under febrile affections, appears to owe its colour chiefly to the purpurate of ammonia, and perhaps occasionally to the purpurate of soda.

The solution of lithic acid in nitric acid stains the skin of a permanent colour, which becomes of a deep purple on exposure to the sun. These apparently sound experimental deductions of Dr. Prout, have been called in question by M. Vauquelin; but Dr. Prout ascribes M. Vauquelin's failure, in attempting to procure purpuric acid, to his having operated on an impure lithic acid. We think entire confidence may be put in Dr. Prout's experiments. He says that it is difficult to obtain purpuric acid from the lithic acid of urinary concretions. Phil. Trans. for 1818. and Annals of Phil. vol. 14.*

ACID (PYROLIGNOUS). In the destructive distillation of any kind of wood, an acid is obtained, which was formerly called acid spirit of wood, and since pyrolignous acid. * Fourcroy and Vauquelin showed that this acid was merely the acetic, contaminated with empyreumatic oil and bitumen. See ACETIC ACID.

Under acetic acid will be found a full account of the production and purification of pyrolignous acid. We shall add here, that M. Monge discovered, about two years ago, that this acid has the property of preventing the decomposition of animal substances. It is sufficient to plunge meat for a few moments into this acid, even slightly empyreumatic, to preserve it as long as you please. "Putrefaction," it is said, "not only stops, but retrogrades." To the empyreumatic oil a part of this effect has been ascribed; and hence has been accounted for, the agency of smoke in the preservation of tongues, hams, herrings, &c. Dr. Jorg of Leipsic has entirely recovered several anatomical preparations from incipient corruption by pouring this acid over them. With the empyreumatic oil or tar he has smeared pieces of flesh already advanced in decay, and notwithstanding that the weather was hot, they soon became dry and sound. To the above statements Mr. Ramsay of Glasgow, an eminent manufacturer of pyrolignous acid, and well known for the purity of his vinegar from wood, has recently added the fol

lowing facts in the 5th number of the Edinburgh Philosophical Journal. If fish be simply dipped in redistilled pyrolignous acid, of the specific gravity 1.012, and afterwards dried in the shade, they preserve perfectly well. On boiling herrings treated in this manner, they were very agreeable to the taste, and had nothing of the disagreeable empyreuma which those of his earlier experiments had, which were steeped for three hours in the acid. A number of very fine haddocks were cleaned, split, and slightly sprinkled with salt for six hours. After being drained, they were dipped for about three seconds in pyrolignous acid, then hung hung up in the shade for six days. Onl On being broiled, the fish were of an uncommonly fine flavour, and delicately white. Beef treated in the same way, had the same flavour as Hamburgh beef, and kept as well. Mr. Ramsay has since found, that his perfectly purified vinegar, specific gravity 1.034 being applied by a cloth or sponge to the surface of fresh meat, makes it keep sweet and sound for several days longer in summer than it otherwise would. Immersion for a minute in his purified common vinegar, specific gravity 1.009, protects beef and fish from all taint in summer, provided they be hung up and dried in the shade. When, by frequent use, the pyrolignous acid has become impure, it may be clarified by beating up twenty gallons of it with a dozen of eggs in the usual manner, and heating the mixture in an iron boiler. Before boiling, the eggs coagulate, and bring the impurities to the surface of the boiler, which are of course to be carefully skimmed off. The acid mustimmediately be withdrawn from the boiler, as it acts on iron.*

* ACID (PYROLITHIC). When uric acid concretions are distilled in a retort, silvery white plates sublime. These are pyrolithate of ammonia. When their solution is poured into that of subacetate of lead, a pyrolithate of lead falls, which, after proper washing, is to be shaken with water, and decomposed by sulphuretted hydrogen gas. The supernatant liquid is now a solution of pyrolithic acid, which yields small acicular crystals by evaporation. By heat these melt and sublime in white needles. They are soluble in four parts of cold water, and the solution reddens vegetable blues. Boiling alcohol dissolves the acid, but on cooling it deposites it, white grains. Nitric acid dissolves without changing it. Hence, pyrolithic is a different acid from the lithic, which, by nitric acid, is convertible into purpurate of ammonia. The pyrolithate of lime crystallizes in stalactites, which have a bitter and slightly acrid taste. It consists of 91.4 acid + 8.6 lime. Pyrolithate of barytes is a nearly insoluble powder. The salts of pot ash, soda, and ammonia, are soluble, and the former two crystallizable. At a red heat, and by passing it over ignited oxide of copper, it is decomposed, into oxygen 44.32, carbon 28.29, azote 16.84, hydrogen 10.*

in small

* ACID (PYROMALIC). When malic or sorbic acid, for they are the same, is distilled in a retort, an acid sublimate, in white needles, appears in the neck of the retort, and an acid liquid distils into the receiver. This liquid, by evaporation, affords crystals, constituting a peculiar acid, to which the above name has been given.

They are permanent in the air, melt at 118o Fahr., and on cooling, form a pearl coloured mass of diverging needles. When thrown on red hot coals, they completely evaporate in an acrid, cough-exciting smoke. Exposed to a strong heat in a retort, they are partly sublimed in needles, and are partly decomposed. They are very soluble in strong alcohol, and in double their weight of water, at the ordinary temperature. The solution reddens vegetable blues, and yields white flocculent precipitates with acetate of lead and nitrate of mercury; but produces no precipitate with lime-water. By mixing it with barytes-water, a white powder falls, which is redissolved by dilution with water, after which, by gentle evaporation, the pyromalate of barytes may be obtained in silvery plates. These consist of 100 acid, and 185.142 barytes, or in prime equivalents, of 5.24 + 9.70.

Pyromalate of potash may be obtained in feather formed crystals, which deliquesce. Pyromalate of lead forms first a white flocculent precipitate, soon passing into a semi-transparent jelly, which by dilution and filtration from the water, yields brilliant pearly looking needles. The white crystals that sublime in the original distillation, are considered by M. Lassaigne as a peculiar acid.*

* ACID (PYROTARTARIC). Into a coated glass retort introduce tartar, or rather tartaric acid, till it is half full, and fit to it a tubulated receiver. Apply heat, which is to be gradually raised to redness. Pyrotartaric acid of a brown colour, from impurity, is found in the liquid products. We must filter these through paper previously wetted, to separate the oily matter. Saturate the liquid with carbonate of potash; evaporate to dryness; redissolve, and filter through clean moistened paper. By repeating this process of evaporation, solution, and filtration, several times, we succeed in separating all the oil. The dry salt is then to be treated in a glass retort, at a moderate heat, with dilute sulphuric acid. There passes over into the receiver, first of all a liquor con

taining evidently acetic acid; but towards the end of the distillation, there is condensed in the vault of the retort, a white and foliated sublimate, which is the pyrotartaric acid, perfectly pure.

It has a very sour taste, and reddens powerfully the tincture of turnsole. Heated in an open vessel, the acid rises in a white smoke, without leaving the charcoaly residuum, which is left in a retort. It is very soluble in water, from which it is separated in crystals by spontaneous evaporation. The bases combine with it, forming pyrotartrates, of which those of potash, soda, ammonia, barytes, strontites, and lime, are very soluble. That of potash is deliquescent, soluble in alcohol, capable of crystallizing in plates, like the acetate of potash. This pyrotartrate precipitates both acetate of lead and nitrate of mercury, whilst the acid itself precipitates only the latter. Rose is the discoverer of this acid, which was formerly confounded with the acetic. *

* ACID (ROSASIC). There is deposited from the urine of persons labouring under intermittent and nervous fevers, a sediment of a rose colour, occasionally asionally in reddish crystals. This was first discovered to be a peculiar acid by M. Proust, and afterwards examined by M. Vauquelin. This acid is solid, of a lively cinnabar hue, without smell, with a faint taste, but reddening litmus very sensibly. On burning coal it is decomposed into a pungent vapour, which has not the odour of burning animal matter. It is very soluble in water, and it even softens in the air. It is soluble in alcohol. It forms soluble salts with potash, soda, ammonia, barytes, strontites, and lime. It gives a slight rose-coloured precipitate with acetate of lead. It also combines with lithic acid, forming so intimate a union, that the lithic acid in precipitating from urine carries the other, though a deliquescent substance, down along with it. It is obtained pure by acting on the sediment of urine with alcohol. Sce Acın (PURPURFC).*

* ACID (SACLACTIC). See ACID (Mucic).* * ACID (SERACIC). Subject, to a considerable heat, 7 or 8 pounds of hog's lard, in a stoneware retort capable of holding double the quantity, and connect its beak by an adopter with a cooled receiver. The condensible products are chiefly fat, altered by the fire, mixed with a little acetic and sebacic acids. Treat this product with boiling water several times, agitating the liquor, allowing it to cool and decanting each time. Pour at last, into the watery liquid, solution of acetate of lead in excess. A white flocculent precipitate of sebate of lead will instantly fall, which must be collected on a filter, washed, and dried. Put the sebate of lead into a phial

and pour upon it its own weight of sulphuric acid, diluted with five or six times its weight of water. Expose this phial to a heat of about 212o. The sulphuric acid combines with the oxide of lead, and sets the sebacic acid at liberty. Filter the whole while hot. As the liquid cools, the sebacic acid crystallizes, which must be washed, to free it completely from the adhering sulphuric acid. Let it be then dried at a gentle heat.

The sebacic acid is inodorous; its taste is slight, but it perceptibly reddens litmus paper; its specific gravity is above that of water, and its crystals are small white needles of little coherence. Exposed to heat, it melts like fat, is decomposed, and partially evaporated. The air has no effect upon it. It is much more soluble in hot than in cold water; hence boiling water saturated with it, assumes a nearly solid consistence on cooling. Alcohol dissolves it abundantly at ordinary temperature.

With the alkalis it forms soluble neutral salts; but if we pour into their concentrated solutions, sulphuric, nitric, or muriatic acids, the sebacic is immediately deposited in large quantity. It affords precipitates with the acetates and nitrates of lead, mercury, and silver.

Such is the account given by M. Thenard of this acid, in the 3d volume of his Traité de Chimie, published in 1815. Berzelius, in1806, published an elaborate dissertation, to prove that M. Thenard's new sebacic acid was only the benzoic, contaminated by the fat, from which, however, it may be freed, and brought to the state of common benzoic acid. M. Thenard takes no notice of M. Berzelius whatever, but concludes his account by stating, that it has been known only for twelve or thirteen years, and that it must not be confounded with the acid formerly called sebacic, which possesses a strong disgusting odour, and was merely acetic or muriatic acid, or fat, which had been changed in some way or other, according to the process used in the preparation.*

* ACID (SORBIC). The acid of apples, called malic, may be obtained most conveniently and in greatest purity from the berries of the mountain ash, called sorbus, or pyrus aucuparia, and hence the present name, sorbic acid. This was supposed to be a new and peculiar acid by Mr. Donovan and M. Vauquelin, who wrote good dissertations upon it. But it now appears that the sorbic and pure malic acids are identical.

Bruise the ripe berries in a mortar, and then squeeze them in a linen bag. They yield nearly half their weight of juice, of the specific gravity of 1.077. This viscid juice, by remaining for about a fortnight

in a warm temperature, experiences the vinous fermentation, and would yield a portion of alcohol. By this change, it has become bright, clear, and passes easily through the filter, while the sorbic acid itself is not altered. Mix the clear juice with filtered solution of acetate of lead. Separate the precipitate on a filter, and wash it with cold water. A large quantity of boiling water is then to be poured upon the filter, and allowed to drain into glass jars. At the end of some hours, the solution deposites crystals of great lustre and beauty. Wash these with cold water, dissolve them in boiling water, filter, and crystallize. Collect the new crystals, and boil them for half an hour in 2.3 times their weight of sulphuric acid, specific gravity 1.090, supplying water as fast as it evaporates, and stirring the mixture diligently with a glass rod. The clear liquor is to be decanted into a tall narrow glass jar, and while still hot, a stream of sulphuretted hydrogen is to be passed through it. When the lead has been all thrown down in a sulphuret, the liquid is to be filtered, and then boiled in an open vessel to dissipate the adhering sulphuretted hydrogen. It is now a solution of sorbic scid.

When it is evaporated to the consistence of a sirup, it forms mammelated masses of a crystalline structure. It still contains a considerable quantity of water, and deli quesces when exposed to the air. Its solution is transparent, colourless, void of smell, but powerfully acid to the taste. Lime and barytes waters are not precipitated by solution of the sorbic acid, although the sorbate of lime is nearly insoluble. One of the most characteristic properties of this acid, is the precipitate which it gives with the acetate of lead, which is at first white and flocculent, but afterwards assumes a brilliant crystalline appearance. With potash, soda, and ammonia, it forms crystallizable salts containing an excess of acid. That of potash is deliquescent. Sorbate of barytes consists, according to M. Vauquelin, of 47 sorbic acid, and 53 barytes in 100. Sorbate of lime well dried, appeared to be composed of 67 acid + 33 lime = 100. Sorbate of lead, which in solution, like most of the other sorbates, retains an acidulous taste, consists in the dried state of 33 acid + 67 oxide of lead in 100. The ordinary sorbate contains 12.5 per cent of water. M. Vauquelin says that Mr. Donovan was mistaken in supposing that he had obtained super and subsorbates of lead. There is only one salt with this base, according to M. Vauquelin. It is nearly insoluble in cold water; but a little more so in boiling water: as it cools it crystallizes in the beautiful white, brilliant, and shining needles, of which we fatory furnace, and to stop up the neck of it till the distillation begins, in order to prevent the materials from attracting fresh humidity from the air. At the beginning of the distillation the retort must be opened, and a moderate fire is to be applied to it, in order to expel from the vitriol all that part of the phlegm which does not taste strongly of the acid, and which may be received in an open vessel placed under the retort. But as soon as there appear any acid drops, a receiver is to be added, into which has been previously poured a quantity of the acidulous fluid which has come over, in the proportion of half a pound of it to twelve pounds of the calcined vitriol; when the receiver is to be secured with a proper luting. The fire is now to be raised by little and little to the most intense degree of heat, and the

air. Dropped into water in small quanti ties, it excites a hissing noise, as if it were red hot iron; in larger quantities it produces a species of explosion. It is said to be convertible into ordinary sulphuric acid, by the addition of a fifth of water. It dissolves sulphur, and assumes a blue, green, or brown colour, according to the proportion of sulphur dissolved. The specific gravity of the black fuming sulphuric acid, prepared in large quantities from copperas, at Nordhausen, is 1.896. Its constitution is not well ascertained.*

The sulphuric acid made in Great Britain is produced by the combustion of sulphur. There are three conditions requisite in this operation. Oxygen must be present to maintain the combustion; the vessel must be so close as to prevent the escape of the volatile matter which rises,

receiver carefully covered with wet cloths, and water must be present to imbibe it.

and, in winter time, with snow or ice, as the acid rises in the form of a thick white vapour, which toward the end of the operation becomes hot, and heats the receiv

er to a great degree. The fire must be continued at this high pitch for several days, till no vapour issues from the retort, nor any drops are seen trickling down its sides. In the case of a great quantity of vitriol being distilled, M. Bernhardt has observed it to continue emitting vapours in this manner for the space of ten days. When the vessels are quite cold, the receiver must be opened carefully, so that none of the luting may fall into it; after which the fluid contained in it is to be poured into a bottle, and the air carefully excluded. The fluid that is thus obtained is the German sulphuric acid, of which Bernhardt got sixty-four pounds from six hundred weight of vitriol; and on the other hand, when no water had been pre. viously poured into the receiver, fifty-two pounds only of a dry concrete acid. This acid was formerly called glacial oil of vitriol, and its consistence is owing to a mixture of sulphurous acid, which occasions it to become solid at a moderate temperature.

* It has been lately stated by Vogel, that when this fuming acid is put into a glass retort, and distilled by a moderate heat into a receiver cooled with ice, the fuming portion comes over first, and may be obtained in a solid state by stopping the distillation in time. This has been supposed to constitute absolute sulphuric acid, or acid entirely void of water. It is in silky filaments, tough, difficult to cut, and somewhat like asbestos. Exposed to the air, it fumes strongly, and gradually evaporates. It does not act on the skin so rapidly as concentrated oil of vitriol. Up to 66° it continues solid, but at temperatures above this it becomes a colourless vapour, which whitens on contact with

For these purposes, a mixture of eight parts of sulphur with one of nitre is placed in a proper vessel, enclosed within a chamber of considerable size, lined on all sides with lead, and covered at bottom with a

shallow stratum of water. The mixture

being set on fire, will burn for a considerable time by virtue of the supply of oxygen which nitre gives out when heated, and the water imbibing the sulphurous vapours, becomes gradually more and more acid after repeated combustions, and the acid is afterward concentrated by distillation.

* Such was the account usually given of this operation, till MM. Clement and Desormes showed, in a very interesting memoir, its total inadequacy to account for the result. 100 parts of nitre, judiciously managed, will produce, with the requisite quantity of sulphur, 2000 parts of concentrated sulphuric acid. Now these contain 1200 parts of oxygen, while the hundred parts of nitre contain only 39 of oxygen; being not 30th part of what is afterwards found in the resulting sulphuric acid. But after the combustion of the sulphur, the nitre is converted into sulphate and bisulphate of potash, which mingled residuary salts contain nearly as much oxygen as the nitre originally did. Hence, the origin of the 1200 parts of the oxygen in the sulphuric acid is still to be sought for. The following ingenious theory was first given by MM. Clement and Desormes. The burning sulphur, or sulphurous acid, taking from the nitre a portion of its oxygen, forms sulphuric acid, which unites with the potash, and displaces a little nitrous and nitric acids in vapour. These vapours are decomposed, by the sulphurous acid, into nitrous gas, or deutoxide of azote. This gas, naturally little denser than air, and now expanded by the heat, suddenly rises

to the roof of the chamber; and might be expected to escape at the aperture there, which manufacturers were always obliged to leave open, otherwise they found the acidification would not proceed. But the instant that nitrous gas comes in contact with atmospherical oxygen, nitrous acid vapour is formed, which being a very heavy aëriform body, immediately precipitates on the sulphurous flame, and converts it into sulphuric acid; while itself resuming the state of nitrous gas, reascends for a new charge of oxygen, again to redescend, and transfer it, to the flaming sulphur. Thus we see, that a small volume of nitrous vapour, by its alternate metamorphoses into the states of oxide and acid, and its consequent interchanges, may be capable of acidifying a great quantity of sulphur.

This beautiful theory received a modification from Sir H. Davy. He found that nitrous gas had no action on sulphurous gas, to convert it into sulphuric acid, unless water be present. With a small proportion of water, 4 volumes of sulphurous acid gas, and 3 of nitrous gas, are condensed into a crystalline solid, which is instantly decomposed by abundance of water; oil of vitriol is formed, and nitrous gas given off, which with contact of air becomes nitrous acid gas, as above described. The process continues, according to the same principle of combination and decomposi

tion, till the water at the bottom of the chamber is become strongly acid. It is first concentrated in large leaden pans, and afterwards in glass retorts heated in a sandbath. Platinum alembics, placed within pots of cast-iron of a corresponding shape and capacity, have been lately substituted in many manufactories for glass, and have been found to save fuel, and quicken the process of concentration.

The proper mode of burning the sulphur with the nitre, so as to produce the greatest quantity of oil of vitriol, is a problem, concerning which chemists hold a variety of opinions. M. Thenard describes the following as the best. Near one of the sides of the leaden chamber, and about a foot above its bottom, an iron plate, furnished with an upright border, is placed horizontally over a furnace, whose chimney passes across, under the botton of the chamber, without having any connexion with it. On this plate, which is enclosed in a little chamber, the mixture of sulphur and nitre is laid. The whole being shut up, and the bottom of the large chamber covered with water, a gentle fire is kindled in the furnace. The sulphur soon takes fire, and gives birth to the products described. When the combustion is finished, which is seen through a little pane adapted to the trap-door of the chamber,

VOL. I.

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this is opened, the sulphate of potash is withdrawn, and is replaced by a mixture of sulphur and nitre. The air in the great chamber is meanwhile renewed, by opening its lateral door, and a valve in its opposite side. Then, after closing these openings, the furnace is lighted anew. Successive mixtures are thus burned till the acid acquires a specific gravity of about 1.390, taking care never to put at once on the plate more sulphur than the air of the chamber can acidify. The acid is then withdrawn by stopcocks, and concentrated.

The following details are extracted from a paper on sulphuric acid by Dr. Ure, which was published in the 4th volume of the Journal of Science and the Arts.

The best commercial sulphuric acid that I have been able to meet with, contains from one-half to three quarters of a part in the hundred, of solid saline matter, foreign to its nature. These fractional parts consist of sulphate of potash and lead, in the proportion of four of the former to one of the latter. It is, I believe, difficult to manufacture it directly, by the usual methods, of a purer quality. The ordinary acid sold in the shops contains often 3 or 4 per cent. of saline matter. Even more is occasionally introduced, by the employment of nitre, to remove the brown colour given to the acid by carbonaceous matter. The amount of these adulterations, whether accidental or fraudulent, may be readily determined by evaporating, a small capsule of porcelain, or rather platinum, a definite weight of the acid. The platinum cup, placed on the red cinders of a common fire, will give an exact result in five minutes. If more than five grains of matter remain from five hundred of acid, we may pronounce it sophisticated.

Distillation is the mode by which pure oil of vitriol is obtained. This process is described in chemical treatises as both difficult and hazardous; but since adopting the following plan, I have found it perfectly safe and convenient. I take a plain glass retort, capable of holding from two to four quarts of water, and put into it about a pint measure of the sulphuric acid, (and a few fragments of glass,) connecting the retort with a large globular receiver, by means of a glass tube four feet long, and from one to two inches in diameter. The tube fits very loosely at both ends. The retort is placed over a charcoal fire, and the flame is made to play gently on its bottom. When the acid begins to boil. smartly, sudden explosions of dense vapour, rush forth from time to time, which would infallibly break small vessels. Here, however, these expansions are safely permitted, by the large capacity of the retort and receiver, as well as by the easy communication with the air at both ends of the

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