(510.) Oxygen gas is commonly fuppofed to be fome unknown fubftance, in combination with caloric, or latent heat. But as this fubftance has never been difcovered in a feparate ftate, the gas is treated as a fimple fubftance. This gas was firft difcovered by Dr Pricftley in 1774, who gave it the name of dephlogifticated air. It was after wards called highly respirable air; and Scheele, who difcovered it in 1775, gave it the name of empyreal air. Condorcet and others gave it the name of vital air; and Lavoisier, when he improved the nomenclature of chemistry, affigned it the name of oxygen gas. For the difcovery of this fubftance we are wholly indebted to modern chemistry; and as it is of moft extenfive influence, not only in the operations of chemistry, but also in thofe of nature and the arts, its nature and properties may well deferve a very full difcuffion. (511.) In order to procure this fubftance, a retort of iron, or of glas coated with clay, or of glazed earthen ware, or porcelain, muft be ufed. To the neck of this retort, after the fubftance from which the gas is to be extracted is put into it, a bent tube is adapted, and closely luted. The bent tube paffes over the edge of the pneumatic trough, and terminates below a fhelf on which is placed a glass jar previoufly filled with water. After the gas begins to rife, as much fhould be allowed to efcape as will fully compenfate for the air in the veifels; after which the mouth of the bent tube being put under the jar in the trough, the oxygen gas will arife in bubbles, and difplace the water in the jar, and occupy its place. In this jar it may be kept for ufe, and transferred to other veffels for any purpose wanted.

(512). 1. Into the iron retort put a quantity of

oxygen gas will rife very copioufly when the tort begins to get red hot.

(513.) 2. In a coated glafs, or glazed earthers tort, a quantity of the black powder of ma nese may be put, which has as much strong fute ric acid added to it, as is fufficient to form th whole into a pafte. This preparation yields gen gas, which fhould be collected in the fi way as the former: only to make the gas rife fr the manganefe, it is not neceflary to apply much heat to the retort in this as in the toma cafe. The reafon affigned by chemifts is, that e fulphuric acid, by combining with the mate nefe, paffes into the ftate of a folid body, a gives out its caloric of fluidity to the oxy which caufes it to affume its aerial or elaffic form We have already expreffed doubts whether the be a true account of the matter; but when phuric acid is ufed, the retort must not be of iro or any fubftance on which the acid would act. A leaden retort would anfwer.

(514) 3. Oxygen may alfo be obtained from red oxide of mercury, heated in a coated glais, a glazed earthen retort.

(515) 4. It may alfo be obtained from the lit called nitre, or faltpetre, when heated red hot a retort, and treated as already directed. A go barrel, whofe touch hole is clofely plugged may ferve as a retort for this falt, or for the back oxide of manganefe. A gun-barrel, whole breech is fawed off, may ferve as an intermediate tube, convey the gas from the retort in the furnace, the crooked tube which conveys it under the in the pneum tic trough. Although nitre di not yield oxygen fo copionfly as the other ma rials, what it yields is of greater purity: beca a portion of manganefe, or of fulphurous or other gafes, always goes over with the oxygen from the other materials.

(516.) The jars, after being filled with the may be removed from the pneumatic trough, b clapping under them a flat difh filled with watch on which they may be carried where wanted, and allowed to stand any length of time. The wat in the difh will prevent communication betwe the atmospheric air, and the oxygen in the Or portions of the oxygen may be transferred t other vefiels, a phial for inftance, by previoufy ling the phial with water, and holding it above the furface of the water in the pneumatic trough with one hand, while with the other the jar of ygen is funk below the mouth of the phial, and turned fo that bubbles of gas may rife from the upper edge of the jar into the mouth of the phin fo as to difplace the water, and fill it. If the mouth of the phial be fo narrow that the bubi of gas are apt to pafs by, without entering it, a fmall funnel inferted in it will conduct them up wards into the phial. When the jar is in the form of a bell, and has a fmall brafs cape and top-e on its top, the gas may be taken out at top, b opening the ftop-cock, and finking the bell d in the deep part of the pneumatic trough, beide the shelf." Thefe obfervations apply to the

manganefe in powder, and having luted on the nagement of all gafes as well as oxygen; al bent tube, put the retort into a furnace or into a fome of them require a pneumatic trough filled with mercury, in place of water. (517) The oxygen gas, thus obtained, i

niked fire, and having placed the end of the bent tube under the jar in the pneumatic trough, the

Uranium,
Molybdena,

Tungsten,

Cobalt,

it fhould be filled with refufe of iron wire, or w the borings of iron guns. A bent tube is inferted in the oppofite extremity of the earthen tube, and conveys the gas under the jars placed in the pr matic trough. In this cafe the water is dece pofed; its oxygen combining with iron, whieh hydrogen affumes its elaftic, or gafeous form.

(526.) Hydrogen gas was long known to mice and was the caufe of much terror to them, unde the names of wild fire, and fire damp. Not may years ago a great quantity of this gas was ref exploded in a coal-pit at Cambuflang, near G gow which killed fome of the miners and fa ed others; fhook the earth all around; caufor pit to close; and blew away the horse-gin, a ther machinery at the mouth of the pit, f no fragment of them was ever found. At N caftle, and other coal-diftricts, they have a conical building, like a glafs-houfe furnace, around the mouth of a pit which is funk te the rife of the coal-ftratum. This building c tered by 3 or 4 doors, whofe junctions are with cloth, and are opened and shut in fore fo that no air can get into the building but rifes up thro' the pit. A powerful fire is contr ly kept up in this building, which caufes a firing draught of air to rife up thro' the pit, and to lighter than common air always rifes pa vey along with it the hydrogen gas, which be Atmospheric air is admitted by the funk towards the dip, or inclination of the pits ftratum; and thus their mines are ventilated conftant fucceffion of fresh air, while the by gen gas is drawn off-Hydrogen gas is fupp to be generated in mines from the decompos of water by means of pyrites, or of coal.

thic

SECT. II. Of HYDROGEN GAS. (523) Hydrogen gas is a tranfparent, elastic, aerial fluid, of much lefs fpecific gravity than atmofpheric air, and hence is commonly ufed for filling balloons. It is an inflammable fubftance, and is commonly reckoned a fimple or elementary body; though, if the received theory concerning the conftitution of gafeous bodies be true, of which we have often expreffed our doubts, it muft, like oxygen, be a compound of caloric with fome unknown bafis. Being highly inflammable, (527.) Mayow, Boyle, and Hales made fest it was formerly known under the name of inflam mable air; and fome chemifts gave it the name of buitibility was known about the beginning experiments upon this fubftance; and its e pblogiton. As the union of a certain portion of 17th century, and was often exhibited by ft. oxygen with this gas, by means of combuftion, men. But for any diftinct knowledge of produces water. Lavoifier gave it the name of by-ture and properties, we are indebted to Mr Cardrogen, or the bafis of water. dith; whofe inveftigations were followed cut! Prieftley, Scheele, and Volta.

(524.) To procure hydrogen gas, a common retort may be used, into which is put a quantity of iron filings, and on the filings is poured thro' a glafs funnel two parts of fulphuric acid that had been previously diluted with four times its bulk of water. A violent effervefcence enfues, and the point of the retort being held under water until the gas has expelled all the air formerly in the vef. fel, it may be placed below a jar in the pneumatic trough, previously filled with water; the hydrogen gas will rife in copious bubbles, difplace the water, and fill the jar. Sometimes a phial is ufed, into whofe neck a bent tube is inferted, ground with emery. The filings and acid being put into the phial, the bent tube is inferted, and made right, and its extremity being funk under water until all the air is expelled, the gas is then collected in jars placed on the fhelf of the pneumatie trough, as before.

(525.) Hydrogen gas may alfo be procured in great abundance by causing the team of water to thro' a gun barrel that is heated red-hot by beir laid across a fall furnace, or craddle grate, filed with burning coals. A glazed earthen or porcel de tube anfvers best for this purpofe, and

(528.) This gas, like atmospheric air, is f tible of indefinite dilatation and compreffion; the moft probable method for fupporting aerial voyage in balloons, would be to have g quantities of the gas condenfed in globes of per, to be carried as ballaft in the car. Whet ted, the wafte might be occafionally fuppl gas in the balloon began to be too much ext opening a ftop-cock in one of thefe globe after all the globes were emptied of condenied the balloon might ftill be kept afloat by throw. them out from time to time. In this way a loon might be kept afioat a fufficient time to nable an aeronaut to traverfe the ocean.

1.

from diluted fulphuric acid acting on fron
(529) The hydrogen gas which is prode
peculiar fmell fimilar to that which is prod
cribed to fome impurity united with the gas
by flints rubbing on each other. This muf.
the gas produced by fteam patling thro' tub
led with red hot iron, has no fmell. The la
alfo of lefs ipecific gravity than the former,
hence beft adapted for filling balloons.
(530.) This is the lighteft of all the gako

dies yet known. The fpecific gravity of common gas about a minute without feeling much uneafiair being reckoned 'coo, that of hydrogen gas, nefs.-Hydrogen, therefore, can hardly be reckon according to Mr Kirwan, will be o'0843. Accord- ed a refpirable gas: tho' when much diluted with ing to Lavoisier it is only o0756; while Meffrs common air it may be breathed without injury. Fourcroy, Vauquelin, and Seguin, make it o'0887. (534.) Dr Thomson estimates the igniting point Thefe difcrepancies are probably owing to diffe- of this gas at rooo. If a phial be filled with it, rent degrees of purity of the gas on which they o- and a lighted taper applied to its mouth, it burns perated; and we have already ftated that what is flowly, with a yellowish white flame, if it be pure. obtained from steam is lighter and more pure, But if the gas hold other fubftances in folution, than that which is obtained from fulphuric acid the colour of the flame varies according to the subacting upon iron. But Mr Kirwan's eftimate is ftance; tho' it is commonly reddith. It may alfo mot likely to be correct. At the temperature of be fet on fire by a red hot iron, or by the electric 60°, and the barometer ftanding at 30 inches. fpark; but not by fparks ftruck from flints by According to Kirwan, 100 cubic inches of this gas fteel. Hence, in fome mines, where they are aweigh 2613 grains Troy; according to Lavoifier, fraid of producing explefions of this gas, instead 373 grains; and according to Fourcroy, Vauque of candles, they produce light by means of a lin, and Seguin 2'75 grains. Thus hydrogen gas ratchet wheel of Iteel, which being turned rapid is nearly 12 times lighter than common air; and ly round, ftrikes fire by fcratching flints fixed, in Tome eftimate that which is obtained from fteam the rim of another wheel. paffed over hot iron in a tube, to be 13 times lighter than common air.-The lightness of this gas accounts for its buoyancy, in raifing balloons Eto the higher regions of the atmosphere.

($31.) If a lighted taper, or any burning body, be immerfed in this gas, it is inftantly extinguifh ed. Hence it is not a fupporter of combustion. (532) Tho' it does not inftantly extinguifh animal life, it is not capable of fupporting refpiration any length of time. Dr Gilby of Birmingham found a moufe lived in it 30 feconds, without apparent inconvenience; but in one minute and thirty two feconds it was dead. Dr Beddoes kept a rabbit in it 7 minutes, and tho' it was much diftreffed, it recovered. Toads, and fome animals of that fort, can live in it a very long time; but in fuch fituations there is reason to fufpect that they revert to their dormant, or lethargic ftate. (533) Scheele could make 20 infpirations of it without much inconvenience. This Fontana afcribed to common air previously contained in the lungs, for after emptying his lungs as much as poffible, he could only make three refpirations of this gas, and thefe accompanied with extreme feebleness and oppreffion about the cheft. There is, however, reafon to fufpect that the gas he breathed was carbureted hydrogen, which is very deleterious; for Pilatre de Rofier, and Mr Watt, confirmed what had been advanced by Scheele. The former, to prove it was real hydrogen gas he took into his lungs, put a pipe into his mouth, and on applying a lighted taper to its extremity when he was blowing it out, the gas burnt with a bright flame. To prove that the refpiration was not fupported by common air previoully in his lungs, he mixed one part of common air with ine of hydrogen gas, and having drawn it into bis lungs, he applied a taper to burn it as before. But it exploded violently in his mouth, producing painful fenfation as if all his teeth had been knocked out. The common air, in this cafe, had not been acted upon by the lungs, or it would not have fupported the combuftion of the hydrogen 25. Mr Davy, of the Royal Inftitution, when his lungs were previously much exhaufted of common air, could not breathe this gas above half a inute, without lofs of mufcular power, and feeling a fort of giddinefs. But when his lungs were not previously emptied, he could breathe this

VOL. V. PART I

(535.) If pure oxygen and hydrogen gas be mixed together, no effect enfues. But if an electric fpark, or a lighted taper be applied to the mixture, it explodes with great violence. If one mea. fure of pure oxygen gas, and 2'05 measures, or bulks, of pure hydrogen gas, be introduced into a jar in the pneumatic trongh, over water, and exploded by the electric fpark, after the explosion, the water fuddenly rifes and fills the whole jar This difcovery we owe to Mr Scheele; but it was followed out by Mr Cavendish with all the accu racy which diftinguishes his chemical refearches. He exploded thefe mixtures in dry glaís vessels, having previously dried the gafes with the utmost care, and always found that, after the explosion, a quantity of water was left in the vessels, exactly equal in weight to that of the oxygen and hydrogen gafes exploded. The gafes wholly difappearing during the explofion, and water being left in the form of fteam, which foon condenfed and formed drops on the fides of veffels, Mr Cavendish concluded that water is compounded of oxygen and hydrogen, united in the proportion of 85 parts by weight of oxygen, with 14 of hydrogen. This conclufion was afterwards more fully cora firmed by the experiments of Lavoifier and his friends.

(535) If a large bladder be filled with hydrogen gas, and a pin-hole made in the end of the bladder, thro' which the gas is preffed in a conftant ftream, it will burn like a candle on applying a lighted taper to the ftream. If it be barnt under a cold glafs bell, its furface will foon be coated with drops of water. If the bladder be hung up for fome time, the atmospheric air will enter and mix with the gas; or if it has the proper propor tion of oxygen gas mixed with it, on applying fire the whole will fuddenly explode. This is the faieft way of exploding this gas, becaufe the fragments of the bladder, when thrown about, can hurt nothing.

(537.) Hydrogen gas, like other combustible bodies, does not burn unless it be in contact with oxygen gas. It requires 9 meafures of common air, at an average, to burn, or explode 4 measures of hydrogen gas, and 7 meatures remain after the combuftion. The hydrogen and the oxygen of the atmospheric air are converted into water while the 7 meafures of gas that remain unchang

XX

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