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dies, resembles the action of capillary tubes on liquids. When a piece of charcoal, charged with one gas, is transferred into another, it absorbs some of it, and parts with a portion of that first condensed. In the experiments of Messrs. Allen and Pepys, charcoal was found to imbibe from the atmosphere in a day about 1-8th of its weight of water. For a general view of absorption, see GAS.

When oxygen is condensed by charcoal, carbonic acid is observed to form at the end of several months. But the most remarkable property displayed by charcoals impregnated with gas, is that with sulphuretted hydrogen, when exposed to the air or oxygen gas. The sulphuretted hydrogen is speedily destroyed, and water and sulphur result, with the disengagement of considerable heat. Hydrogen alone has no such effects. When charcoal was exposed by Sir H. Davy to intense ignition in vacuo, and in condensed azote, by means of Mr. Children's magnificent voltaic battery, it slowly volatilized, and gave out a little hydrogen. The remaining part was always much harder than before; and in one case so hard as to scratch glass, while its lustre was increased. This fine experiment may be regarded as a near approach to the production of diamond.* Charcoal has

a

powerful affinity for oxygen, whence its use in disoxygenating metallic oxides, and restoring their base to its original metallic state, or reviving the metal. Thus too it decomposes several of the acids, as the phosphoric and sulphuric, from which it abstracts their oxygen, and leaves the phosphorus and sulphur free.

* Carbon is capable of combining with sulphur, and with hydrogen. With iron it forms steel; and it unites with copper into a carburet, as observed by Dr. Priestley.

A singular and important property of charcoal is that of destroying the smell, colour, and taste of various substances: for the first accurate experiments on which we are chiefly indebted to Mr- Lowitz of Petersburgh, though it had been long before recommended to correct the fætor of foul ulcers, and as an antiseptic. On this account it is certainly nly the best dentifrice. Water that has become putrid by long keeping in wooden casks, is rendered sweet by filtering through charcoal powder, or by agitation with it; particularly if a few drops of sulphuric acid be added. Common vinegar boiled with charcoal powder becomes perfectly limpid. Saline solutions, that are tinged yellow or brown, are rendered colourless in the same way, so as to afford perfectly white crystals. The impure carbonate of ammonia obtained from bones, is deprived both of its colour and fetid smell by sublimation with an equal weight of charcoal powder. Malt spirit is freed

from its disagreeable flavour by distillation from charcoal; but if too much be used, part of the spirit is decomposed. Simple maceration, for eight or ten days, in the proportion of about 1-150th of the weight of the spirit, improves the flavour much. It is necessary, that the charcoal be well burned, brought to a red heat before it is used, and used as soon as may be, or at least be carefully excluded from the air. The proper proportion too should be ascertained by experiment on a small scale. The charcoal may be used repeatedly, by exposing it for some time to a red heat before it is again employed.

Charcoal is used on particular occasions as fuel, on account of its giving a strong and steady heat without smoke. It is em. ployed to convert iron into steel by cementation. It enters into the composition of gunpowder. In its finer states, as in ivory black, lampblack, &c. it forms the basis of black paints, Indian ink, and printers' ink.

* The purest carbon for chemical purposes is obtained by strongly igniting lampblack in a covered crucible. This yields, like the diamond, unmixed carbonic acid by combustion in oxygen.

a

Carbon unites with all the common simple combustibles, and with azote, forming a series of most important compounds. With sulphur it forms curious limpid liquid called carburet of sulphur, or sulphuret of carbon. With phosphorus it forms a species of compound, whose properties are imperfectly ascertained. It unites with hydrogen in two definite proportions, constituting sub-carburetted and carburetted hydrogen gases. With azote it forms prussic gas, the cyanogen of M. Gay-Lussac. Steel and plumbago are two different compounds of carbon with iron. In black chalk we find this combustible intimately associated with silica and alumina. The primitive combining proportion, or prime equivalent of carbon, is 0.75 on the oxygen scale.*

* CARBON (MINERAL), is of a grayishblack colour. It is charcoal, with various proportions of earth and iron, without bitumen. It has a silky lustre, and the fibrous texture of wood. It is found in small quantities, stratified with brown coal, slate coal, and pitch coal.*

* CARBONATES. Compounds of carbonic acid with the salifiable bases. They are composed either of one prime of the acid and one of the base, or of two of the acid and one of the base. The former set of compounds is called carbonates, the latter bicarbonates. See CARBONIC ACID.

As the system of chemical equivalents, or atomic theory of chemical combination, derives some of its fundamental or prime proportions from the constitution of the carbonates, their analysis requires peculiar precautions. In the Annals of Philosophy for October 1817, I gave a description of a new instrument for accomplishing this purpose with the minutest precision.

the other is open and recurved like a sy. phon. The straight part of the tube, between the ball and bend, is about 7 inches long. The capacity, exclusive of the curved part, is a little more than 5 cubic inches. It is accurately graduated into cubic inches and hundredth parts, by the successive additions of equal weights of quicksilver, from a measure thermometric tube. Seven troy ounces and 66 grains of quicksilver occupy the bulk of one cubic inch. Four and a half such portions being introduced, will fill the ball, and the beginning of the stem. The point in the tube, which is a tangent to the surface of the mercury, is marked with a file or a diamond. Then 344 grains, equal in volume to 1-100th of a cubic inch, being drawn up into the thermometric tube, rest at a certain height, which is also marked. The same measure of mercury is successively acid + 55 lime. introduced and marked off, till the tube is

The usual mode of analysis is to put a given weight of the carbonate in a phial, and add to it a certain quantity of a liquid acid which will dissolve the base, and disengage the carbonic acid. I found, with every care I could take in this method, that variable and uncertain quantities of the liquid acid were apt to be carried off in vapour with the carbonic gas, while a portion of this gasecus acid was generally retained in the saline liquid. Hence, in the analysis of crystallized carbonate of lime, the most uniform of all compounds, we have the following discordant results, which are of importance in the doctrine of equivalents:

Mr. Kirwan makes it consist of

+56 + 56.1

[blocks in formation]

+ 56.3

M. Vauquelin,

43.5

M. Thenard,

43.28

Dr. Thomson,

43.137

+ 56.5 +56.72 + 56.863

If we deduce the equivalent of lime from the analysis of Dr. Marcet, so well known for his philosophical accuracy we shall have Lime 35.1 to carb. acid 27.5

Dr. Thomson's is 36.25 to do. 27.5

I adduced the following experiment, selected from among many others, as capable of throwing light on the cause of these variations: "Into a small pear-shaped vessel of glass, with a long neck, and furnished with a hollow spherical stopper, drawn out, above and below, into a tube almost capillary, some dilute muriatic acid was put. The whole being poised in a delicate balance, 100 grains of calc spar in rhomboidal fragments were introduced, and the stopper was quickly inserted. A little while after the solution was completed, the diminution of weight, indicating the loss of carbonic acid, was found to be 42.2 grains. Withdrawing the stopper, inclining the vessel to one side for a few minutes, to allow the dense gas to flow out, the diminution became 43.3. Finally, on heating the body of the vessel to about 70°, while the hollow stopper was kept cool, small bubbles of gas escaped from the liquid, and the loss of weight was found to be 43.65, at which point it was stationary. This is a tedious process." The instrument which I subsequently employed is quick in its operation, and still more accurate in its results. It consists of a glass tube of the same strength and diameter with that usually employed for barometers, having a strong egg-shaped bulb, about 2 inches long, and 14 wide, blown at one of its ends, while VOL. I.

filled.

"In the instrument thus finished, 1-200th of a cubic inch occupies on the stem about 1-14th of an inch, a space very distinguishable. The weight of carbonic acid, equivalent to that number, is less than 1-400th of a grain. The mode of using it is perfectly simple and commodious, and the analytical result is commonly obtained in a few minutes."

1

400000

For example, five grains of calcareous spar in three or four rhomboids were weighed with great care in a balance by Crighton, which turns with 40이이이이 of the weight in the scales. These are introduced into the empty tube, and made to slide gently along into the spheroid. The instrument is then held in nearly a horizontal position with the left hand, the top of the spheroid resting against the breast, with a small funnel bent at its point, inserted into the orifice of the tube. Quicksilver is now poured in till it be filled, which in this position is accomplished in a few seconds. Should any particles of air be entangled among the mercury, they are discharged by inverting the instrument, having closed the orifice with the finger. On reverting it, and tapping the ball with the finger, the fragments of spar rise to the top. Three or four hundredth parts of a cubic inch of mercury being displaced from the mouth of the tube, that bulk of dilute muriatic acid is poured in; then pressing the forefinger on the orifice, and inclining the instrument forwards, the acid is made to rise through the quicksilver. This, as it is displaced by the cooled carbonic acid, falls into a stone-ware or glass basin, within which the instrument stands in a wooden frame. When the solution is completed, the apparent volume of gas is noted, the mercury in the two legs of the

34

syphon is brought to a level, or the difference of height above the mercury in the basin is observed, as also the temperature of the apartment, and the height of the barometer. Then the ordinary corrections being made, we have the exact volume of carbonic acid contained in five grains of calc spar. In very numerous experiments, which I have made in very different circumstances of atmospherical pressure and temperature, the results have not varied one-hundredth of a cubic inch, on five grains, care being had to screen the instrument from the radiation of the sun or a fire.

As there is absolutely no action exercised on mercury by dilute muriatic acid at ordinary temperatures; as no perceptible difference is made in the bulk of air, by introducing to it over the mercury a little of the acid by itself; and as we can expel every atom of carbonic acid from the muriate of lime, or other saline solution, by gently heating that point of the tube which contains it, it is evident that the total volume of gaseous product must be accurately determined. When a series of experiments is to be performed in a short space of time, I wash the quicksilver with

water, dry it with a sponge first, and then

with warm muslin. The tube is also wash-
ed out and drained. According to my ex-
periments with the above instrument, 5
grains of calcareous spar yield, 4.7 cubic
inches of carbonic acid, equivalent to 43.616
per cent. The difference between this num-
ber and Dr. Wollaston's is inconsiderable.
Among other results which I obtained
from the use of the above instrument, it
enabled me to ascertain the true composi-
tion of the sublimed carbonate of ammo-
nia, which chemists had previously mis-
taken. I showed in the Annals of Philoso-
phy for September 1817, that this salt con-
tained 54.5 of carbonic acid, 30.5 ammo-
nia, and 15 water, in 100 parts; numbers
which, being translated into the language
of equivalents, approach to the following

proportions:-
Carbonic acid, 3 primes,
Ammonia,
Water,

2

2

8.25

55.89

15.25

14.76 100.00

These near approximations to the equivalent ratios in compounds of a variable nature, do not seem to have attracted notice at the time. Dr. Thomson describes in his System the solid subcarbonate found in the shops as indefinite in the proportion of its constituents. In the 14th Number of the Journal of Science, his friend, Mr. Phillips, whose attention to minute accuracy is well known, has published an ingenious paper on the subject, which begins with the following handsome acknowledgment of my labours: "During some late researches, my attention being directed to the composition of the carbonates of ammonia, I began, and had nearly completed an examination of them, before I observed that they had been recently analyzed by Dr. Ure; and I consider his results to be so nearly accurate, that I should have suppressed mine, if I had not noticed some circumstances respecting the compounds in question, which have, I believe, hitherto escaped observation."

Mr. Phillips's communication is valuable. It presents a luminous systematic view of the carbonates of ammonia and soda. Dr.

Thomson, in his Annals for July 1820,

enumerates that account of the carbonates of ammonia among the improvements made in 1819, without any allusion to my experiments on the ammoniacal salts, published in his own Magazine, nearly three years before he printed his retrospect.

The indications of the above analytical instrument are so minute, as to enable us, by the help of the old and well known theorem for computing the proportions of two metals from the specific gravity of an alloy, to deduce the proportions of the bases from the volume of gas disengaged by a given weight of a mixed carbonate. A chemical problem of this nature was practically solved by me, in presence of two distinguished Professors of the University of Dublin, in May 1816. But such an application is more curious than useful, since a slight variation in the quantity of gas, as

4.26 28.86 well as accidental admixtures of other sub-
2.25
stances, are apt to occasion considerable
errors. It determines, however, the nature
and value of a limestone with sufficient
practical precision. As 100 grains of mag-
nesian limestone yield 99 cubic inches of
gas, a convenient rule for it is formed when
we say, that 10 grains will yield 10 cubic
inches. In the same way marls and com-
mon limestones may be examined, by sub-
jecting a certain number of grains, in a
graduated syphon tube, to the action of a
little muriatic acid over mercury. From the
bulk of evolved gas, expressed in cubic inches
and tenths, deduct 1-20th, the remainder will
express the proportion of real limestone pre-
sent in the grains employed.*

As this volatile salt possesses the curious property of passing readily from one system of definite proportions to another, absolute accordance between experiment and theory cannot be expected. The other salt gave for its constituents, 54.5 carbonic acid+22.8 ammonia+22.75 water 100. Now, if these numbers be referred to Dr. Wollaston's oxygen scale, we shall have,Theory. Expt. 2 primes carbonic acid, 5.50 55.66 54.50

1

2

ammonia 2.13 21.56 22.80
water,
2.25 22.78 22.75

[blocks in formation]

* CARBONIC OXIDE. A gaseous compound of one prime equivalent of carbon, and one of oxygen, consisting by weight of 0.75 of the former, and 1.00 of the latter. Hence the prime of the compound is 1.75, the same as that of azote. This gas cannot be formed by the chemist by the direct combination of its constituents; for at the temperature requisite for effecting a union, the carbon attracts its full dose of oxygen, and thus generates carbonic acid. It may be procured by exposing charcoal to a long continued heat. The last products consist chiefly of carbonic oxide.

To obtain it pure, however, our only plan is to abstract one proportion of oxygen from carbonic acid, either in its gaseous state, or as condensed in the carbonates. Thus by introducing well calcined char coal into a tube traversing a furnace, as is represented plate I. fig. 2.; and when it is heated to redness, passing over it backwards and forwards, by means of two at tached mercurial gasometers or bladders, a slow current of carbonic acid, we convert the acid into an oxide more bulky than itself. Each prime of the carbon becomes now associated with only one of oxygen, instead of two, as before. The carbon acting here, by its superior mass, is enabled to effect the thorough saturation of the oxygen.

If we subject to a strong heat, in a gun barrel or retort, a mixture of any dry earthy carbonate, such as chalk, or carbonate of -strontites, with metallic filings or charcoal, the combined acid is resolved as before into the gaseous oxide of carbon. The most convenient mixture is equal parts of dried chalk and iron, or zinc filings. By passing a numerous succession of electric explosions through one volume of carbonic acid, confined over mercury, two volumes of ⚫carbonic oxide, and one of oxygen, are formed, according to Sir H. Davy.

The specific gravity of this gas is stated by Gay-Lussac and Thenard, from theoretical considerations, to be 0.96782, though Mr. Cruickshank's experimental estimate was 0.9569. As the gas is formed by with drawing from a volume of carbonic acid half a volume of oxygen, while the bulk - of the gas remains unchanged, we obtain its specific gravity by subtracting from that of carbonic acid half the specific gravity of oxygen. Hence 1.5277 0.5555 = 0.9722, differing slightly from the above, in consequence of the French chemists

rating the specific gravity of the two eriginal gases at 1.51961 and 1.10359. Hence 100 cubic inches weigh 29 grains at mean pressure and temperature.

This gas burns with a dark-blue flame. Sir H. Davy has shown, that though carbonic oxide in its combustion produces less heat than other inflammable gases, it may be kindled at a much lower temperature. It inflames in the atmosphere, when brought into contact with an iron wire heated to dull redness, whereas carburetted hydrogen is not inflammable by a similar wire, unless it is heated to whiteness, so as to burn with sparks. It requires, for its combustion, half its volume of oxygen gas, producing one volume of carbonic acid. It is not decomposable by any of the simple combustibles, except potassium and sodium. When potassium is heated in a portion of the gas, potash is formed with the precipitation of charcoal, and the disengagement of heat and light. Perhaps iron, at a high temperature, would condense the oxygen and carbon by its strong affinity for these substances. Water condenses of its bulk of the gas. The above processes are those usually prescribed in our systematic works, for procuring the oxide of carbon. In some of them, a portion of carbonic acid is evolved, which may be withdrawn by washing the gaseous product with weak solution of potash, or milk of lime. We avoid the chance of this impurity by extricating the gas from a mixture of dry carbonate of barytes and iron filings, or of oxide of zinc, and previously calcined charcoal. The gaseous product, from the first mixture, is pure oxide of carbon. Oxide of iron, and pure barytes, remain in the retort. Carbonic oxide, when respired, is fatal to animal life. Sir H. Davy took three inspirations of it, mixed with about one-fourth of common air; the effect was a temporary loss of sensation, which was succeeded by giddiness, sickness, acute pains in different parts of the body, and extreme debility. Some days elapsed before he entirely recovered. Since then, Mr. Witter of Dublin was struck down in an apoplectic condition, by breathing this gas; but he was speedily restored, by the inhalation of oxygen. See an interesting account of this experiment, by Mr. Witter, in the Phil. Mag. vol. 43.

When a mixture of it and chlorine is exposed to sunshine, a curious compound, discovered by Dr. John Davy, is formed, to which he gave the name of phosgene gas. I shall describe its properties in treating of chlorine. It has been called chlorocarbonic acid, though chlorocarbonous acid seems a more appropriate name.*

* CARBUNCLE, a gem highly prized by the ancients, probably the alamandine, a variety of noble Garnet.*

*CARBURET OF SULPHUR. Called also sulphuret of carbon, and alcohol of sulphur.

This interesting liquid was originally obtained by Lampadius in distilling a mixture of pulverized pyrites and charcoal in an earthen retort, and was considered by him as a peculiar compound of sulphur and hydrogen. But MM. Clement and Desormes, with the precision and ingenuity which distinguish all their researches, first ascertained its true constitution to be carburet ted sulphur; and they invented a process of great simplicity, for at once preparing it, and proving its nature. Thoroughly calcined charcoal is to be put into a porcelain tube, that traverses a furnace, at a slight angle of inclination. To the higher end of the tube, a retort of glass, containing sul phur, is luted; and to the lower end is at tached an adopter tube, which enters into a bottle with two tubulures, half full of water, and surrounded with very cold water or ice. From the other aperture of the bottle, a bent tube proceeds into the pneumatic trough. When the porcelain tube is brought into a state of ignition, heat is applied to the sulphur, which subliming into the tube, combines with the charcoal, forming the liquid carburet. The conclusive demonstration of such an experiment was however questioned by M. Berthollet, jun. and Cluzel. But MM. Berthollet, Thenard and Vauquelin, the reporters on M. Cluzel's memoir, having made some experiments of their own upon the subject, concluded that the liquid in question was a compound of sulphur and carbon only.

Finally, an excellent paper was written on the carburet by M. Berzelius and Dr. Marcet, who confirmed the results of MM. Clement and Desormes, and added likewise several important facts.

If about ten parts of well calcined charcoal in powder, mixed with fifty parts of pulverized native pyrites (bisulphuret of iron), be distilled from an earthen retort, into a tubulated receiver surrounded with ice, more than one part of sulphuret of carbon may be obtained. If we employ the elegant process of M. Clement, we must take care that the charcoal be perfectly calcined, otherwise no carburet will be obtained. In their early experiments, they attached to the higher end of the porcelain tube a glass one, containing the sulphur in small pieces, and pushed these successively forwards by a wire passing air-tight through a cork, at the upper end of the

tube.

Besides the liquid carburet, there is formed some carburetted and sulphuretted hydrogen, and a reddish-brown solid and very combustible matter, which seems to be sulphur slightly carburetted. This substance remains almost entirely in the adopt

er tube. The liquid carburet occupies the bottom of the receiver bottle, and may be separated from the supernatant water, by putting the whole into a funnel, whose tube is closed with the finger, and letting the denser brown carburet flow out below, whenever the distinction of the liquid into two strata is complete. Thus obtained, the carburet is always yellowish, containing a small excess of sulphur, which may be removed by distillation from a glass retort, plunged in water, at a temperature of 115°It is now transparent and colourless, of a penetrating, fetid smell, and an acrid burning taste. Its specific gravity varies from 1.263 to 1.272. According to Dr. Marcet, it boils below 110°; according to M. The nard at 113° F.; and the tension of its vapour at 72.5o is equivalent to a column of 12.53 inches of mercury. At 53.5°, according to Marcet and Berzelius, the tension is equivalent to a column of 7.4 inches, or one-fourth of the mean atmospheric pressure; hence one-third is added to the bulk of any portion of air, with which the liquid may be mixed. A spirit of wine thermometer, having its bulb surrounded with cotton cloth or lint, if dipped in sulphuret of carbon, and suspended in the air, sinks from 60° to 0°. If it be put into the receiver of an air pump, and a moderate exhaustion be made, it sinks rapidly from 60° to 81°. If a tube containing mercury be treated in the same way, the mercury may be readily frozen even in summer. The drier the air in the receiver, the more easily is the cold produced. Hence the presence of sulphuric acid may be of some service in removing the vapour from the air in the receiver.

This carburet may be cooled to 80° without congealing; a conclusive proof that combination changes completely the constitution of bodies, since two substances usually solid, form a fluid which we cannot solidify. When a lighted body approaches the surface of the carburet, it immediately catches fire, and burns with a blue sulphurous flame. Carbonic and sulphurous acids are exhaled, and a little sulphur is deposited. A heat of about 700° inflames the vapour of the carburet. Oxygen dilated by it over mercury explodes by the electric spark, with a violent detonation. My eudiometer is peculiarly adapted to the exhibition of this experiment. A portion of oxygen being introduced into the sealed leg, we pour a few drops of the carburet on the surface of the mercury in the open leg, and closing this with the finger, transfer the liquid to the other by a momentary inclination of the syphon. The expansion of volume can be now most accurately measured by bringing the mercury to a level in each leg.

The subsequent explosion occasions no

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