EUD

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in-.’.>.ns of i iirous gas. The result of the minierous experimentswhich fiave been made with n nous g«s is, that the proportion ofox\ gen :jj atmospheric air varies in different places and at differenttimes. Ti.e minimum is about 0.22, the maximum about 0.30;Consequently if this method ol analysing air is to be depended on,we must consider that fluid not as a permanent chemical compound,but as a body subjected to ail the variations to which accidentalmixture': are liable.

2. The second kind of eudiometer was proposed by Volta. Thesubstance employed by that philosopher to separate the oxygenfrom the air was hydrogen gas. fits method was, to mix givenproportions of the air to he examined and hydrogen gas in a gradu-ated giass tube; to fire the mixture by an electric spark; and tojudge of the purity of the air by the hulk of the residuum. Hutrhis inethod is "not susceptible of even so great a degree of accu-racy as the preceding, when the object is to ascertain the precisequantity of o.xvgui gas in a given bulk of air. For if too littlehydrogen gas is mixed with the air, not only the whole of the oxy-gen will not be abstracted, hut a p'oriion ot the azote will disappearm con veij-.ience of the formation of nitric acid. On the other band,if too much hydrogen is added, part of it will remain after thetiring of the mixture, and increase the bulk of the residuum.Volta’s eudiometer, then, though it may have its uses, is scarcelysusceptible of giving us the analysis of air.

3. For the third kind of eudiometer, we are indebted to Scheele .It is merely a g-aduated glass vessel, containing a given quantityof air exposed to newly prepared liquid alkaline or earthy sul-phurets ; or to a mixture of iron-tilings and sulphur, formed into apaste by means of water. The-e substances absorb the whole ofthe oxygen or vital principle of the air, which converts a por-tion of the sulphur into an acid. The oxygen contained in the airthus examined, is judged of by the diminution of bulk which thenil has undergone. This method is not oniv exceedingly simple,but it requires very little address, and y el is susceptible of as greataccuracy as any otner whatever. The’ only objection to which itis liable is its slowness; lor when (lie quantity of air operated on iscoiv-iuerable, several days elapse before the diminution lias readiediis maximum. But tins objection inis been completely obviatedby M. Bp Marti, who lias brought Scheele ’s eudiometer to a stateof peiseUion. lie found that a mixture of iron-filings and sulphurdoes not answer well, because it emits a small quantity of hydrogenRa-, involved by the action of the sulphuric add formed by the ab-s °rplion of tiie oxygen of the air upon the iron ; blit the hydro-gureted s-.dpiiurets, formed by boiling together sulphur and liquid]>ota,s or lime-water, answered the purpose perfectly. These sub-stances, indeed, when newly prepared, have the properly of absorb-ing a small portion of azotic gas; but they lose this property whensaturated with that gas, which i» easily effected by agitating themfor a few minutes with a small portion of atmospheric air. Jiis ap-paratus is merely a glass tube, ten inches long, and rather less thanhalf an inch in diameter, open at one end, anil Hermetically sealedat the other. I he close end is divided into 100 equal parts,having an interval of one line between each division. The use oftliis tube is to measure the portion of air to be employed in the ex-periment. "File tube is tilled with water; and by allowing thewater to run out gradually while the tube is inverted) and the openend kept shut with the linger, the graduated part is exactly tilledvrith air. These hundredth parts of air are introduced into a glassbottle filled with liquid sulphuret of lime previously saturated with: «°tic gas, and capable ot Holding from tfvo to four times ttie bulk°‘ tin- air introduced. The bottle is then to be corked with aS r °und glass stopper, and agitated for live minutes. After this thec °i'k is io he withdrawn while the mouth of the phial is under water,and forth;; greater security, it may be corked and agitated again.After this, the air is to be again transferred to the graduated glasstube, in order to ascertain the diminution of its bulk. Air ex-amined by tins process, suffers precisely the same diminution inwhatever circums ances the experiments are mi.de: no variation>3 observed whether the wind is high or low, or from what quartersoever it blows; whether the air tr.ed is moist or dry, hot or cold ;whether the barometer is high or low. Neither the season of theyear, nor the situation of the place, its vicinity to the sea, tomarshes, or to mountains, makes difference. M. De Marti found'he diminution always between 0,21 and 0.23. Hence we mayPonclude that air is composed of

0.7S azotic gas.

0.22 oxygen gas.

1.00

Scheele indeed found, that the absorption amounted to 0.27 ; butthat was because lie neglected to saturate his sulphuret with azoticgas: for when the portion of azotic gas, which must have beenabsorbed, and which lias been indicated by de Marti, is subtracted,the portion of oxygen in air, and indicated by iiis experiments, is re •rluceci very nearly to 0.22. The trilling variations perceptible inhis experiments wi re no doubt owing to the quantities of the mix-ture ol sulphur and iron, by which he abstracted the oxygen, notbeing exactly the same at different times; the consequence ofwhich would be, an unequal absorption of azotic gas.

4. In the fourth kind of eudiometer, the abstraction of the oxy-gen of air is accomplished by means of phosphorus. This eudio-meter was first proposed by Achard. It was considerably im-proved by Keboul, and by Scguin and Lavoisier ; but llerlhoiletlias lately brought it to a state of perfection, as it is equally simplewith the eudiometer of De Marti, and scarcely inferior ;o it in pre-cision. Instead of the rapid combustion of phosphorus, Ibis lastphilosopher has substituted Us spontaneous combustion, which ab-sorbs the oxygen of air completely ; and when the quantity of airoperated on is small, the process F over in a short time. The wholeapparatus consists in a narrow graduated tube of glass containingthe air to lie examined, into which is introduced a cylinder of phos-phorus fixed upon a glass rod, while the tube stands inverted overwater. The phosphorus should be so long as to traverse nearlythe whole of the air. Immediately white vapours rise from thephosphorus and fill the tube. These continue till the whole oftlie oxygen combines with phosphorus. They consist of phos-phorous acid, which falls by its weight to the bottom of the vessel,and is absorbed by the water. The residuum is merely the azoticgas of the a r, holding a portion of phosphorus in solution. Ber-tholiet lias ascertained, that by this foreign bodv its bulk is in-creased one-iortieth part. Consequently, the bulk otthe residuum,diminished by ^ gives us the bulk of the azotic gas of the air ex-amined ; which bulk, subtracted from tiie original mass of air,gives us the proportion of oxygen gas contained in it. All thedifferent experiments which have been made by means of thiseudiometer, agree precisely in their result, and indicate that theproportions of the ingredients of air are always the same, namely,,about 0.22 part of oxygen gas, and 0.7S of azotic gas. Ber-thollel found these proportions in Egypt and in France , and Dr.Thomson found them constantly in Edinburgh in ali the differentseasons oi the year. Thus we see that the analysis of air by meansof phosphoric-, agrees precisely witli its analysis by means of liydro-guret cl suiphmvts.

5. The lifth eudiometer has been lately proposed by Mr Davy.In it the sub tanee used to absorb the oxygen from air is a solu-tion of sulphate or muriate of iron in water, and impregnated withnitrous gas. A small graduated glass tube, tilled with the air to beexamined, is plunged into the nitrous solution, and moved a littlebackwards and forwards. The whole of the oxygen is absorbed in •a few minutes. The state of greatest absorption ought to bemarked, as the mixture afterwards emits a liitiegas which wouldalter tiie result. By means of this and the two preceding eudio-meters, Mr. Davy examined the; air at Bristol, and found it alwaysto contain about 0.21 of oxygen. Air sent to Dr. Beddoes fromthe coast of Guinea gave exactly the same result. This eudiome-ter, then, corresponds exactly with the two last. In all these dif-ferent methods ot analysing air, it is necessary to operate on gir ofa determinate density, and to take care that the residuum is neithermore condensed nor dilated than the air was when fir.A operatedon. Ifthese things are not attended to, no dependence whatevercan be placed upon the result of tiie experiments, how carefullysoever they may have been performed. Now there are three thingswhich alter the volume of air and other elastic tiuids: 1. A changein the height of tiie barometer. 2. Ail increase or diminution oftheir quantity ; the vessel in which they are contained remainingtiie same, and standing in the same quantify of water or mercurv.3. A change in the temperature of tiie air.

EUDOCIA , or EUDOSIA, a celebrated lady, the daughterof Leontius, a philosopher ot Athens; who gave her such a learn-ed education, that at his death, he left her only a small legacy,

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