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in the deep part, must be placed invertedly on the vessel that is stopped like a bottle, it musi be unshelf, its open end turned down upon one of the stopped, with its orifice downwards in the water, holes; the gass then being conveyed to the under and ihen inclined in such a manner that its neck part of lhe excavation by means of a curved or m?y come under the excavation of the shelf. The other tube, or suffered to escape from its former gass will escape from the boille, and passing vessel, will ascend through the hole into the re- through the hole into the vessel intended to receiver, displacing the water as the quantity of ceive it, will ascend into the form of bubbles as gass increases. This trough may be made of vari. before. Sometimes a bent glass tube, such as apous sizes, according to the purpose for which it is pears connected with the flask in fig. 7, is emplorintended : one of about two feet long, 16 inches ed to conduct the gass under the water or merwide, and 15 high, will be found sufficient for cury into the receiver. Some other methods ocmost experiments. Sometimes, however, a much casionally resorted to, particularly in collecting largerone is necessary; and in laboratories, where gasses for distillations, will be noticed in the ara considerable number of experiments are per- ticle PNEUMATIC APPARATUS. formed, it is also requisite to liave several smaller 4. Dointurion or expansion of gasses. --The infiuence ones, which may be moved when necessary near of caloric, in dilating or expanding bodies, has a furnace, or wherever they may be wanted. Fig. been long known as a fact ; though the laws by 2. represents a jar, being filled with gass, stand- which this influence is regulated are not even now ing in a dish coutaining water, and having two perfectly ascertained. In general it is observed handles to transport the vessels from one cistern that the expansion of bodies is greaiesi in their to another, or for keeping them in reserve when gasseous form, less in their fluid, and least in their the cistern is too full.

solid state; as an example, it is known that the A more commodious method of constructing the expansion of air is more than eight times greater pneumatic trough is shewn in fig. 3. ; where ua, than that of water, and that of water is about 13 is the well to contain the water for filling the res- times greater than that of iron. Vany experisels, &c.; H', a small shelf with holes; and on a ments have been made to ascertain the rate of exlevel with it the surface cc, covered also with pansion in gasses according to the elevation of water; and not more than two or ihree inches temperature; but the results obtained were so distant from the brim; old, depressions, or hol. various, on account chiefly of the want of suttilows, to receive the curved necks of bottles, or cient care to exclude water from the vessels in the curved ends of tubes; eee, vessels invented on which the expansion was measured, that for a lon: the surface of the trough; f, a large shelf under- time no settleri opinion could be formed on the sub. neath to contain vessels for use. Instead of a rec- ject. At lengin, however, the problem engiged tangular, some persons prefer a curvular, and the aitention of two very ingenions and precise others an oval shape for their troughs.

philosophers, whose experimnenin agree in furnishSome of thegasses are capable of being absorbed ing a conclusion as curious as it was mexpected; by water, and therefore cannot be collected by namely, thalihe progress of dilatation is absolutely means of the above apparatus. When that is the equal in all the different kinds of gass; or that all case, mercury must be used ; and on account of the diferent elastic fluids, taken at the same temits gravity and dearness, a smaller trough, formed perature, expand equally by heat: that all the somewhat differently, must be employed; as re- dillerent gasses, frou the lightest to the heaviesi. presented in figs. 1. and ij., of which the first is a talen at temperaiure, are equally expanded by perspective view of the spherical coity and caloric. The experimenis of vir. Dalion were groove to be filled, and something higher with read to the IPhilosophical Soriety at Manchester, mercury: the receiving vessel is likewise to be in October, 1801, and published in 1802: the disa filled with thai meial and in verica. Fig. 5. a ser- serlation of Gay Lussac did not appear in the tion of the same, shewing the inanner of pineing Ann. de Chim. (vol. 13) till more ihan six months the receiver, and the neck of the refort, or other after: our own countryınan most therefore be revessel, from wbich the gass is to be supplied. garded as the original discoverer of this imporiant The receiver ought to be of smaller diameter, and law. Mr. Dalton's erperiments are distinguished much stronger than when waler is employed. A by a simplicity of apparatus which adds greatly lo mereurial trough may be cut out of marble free- their value, as it puts it in the power of others to stone, or a solid block of wood; hut the first is repeat them without difficulty. It consists merely preferable. A trough of about 1 inches long, 3 of a glass tube, open at one end, and divided into wide, and 4 deep, besides the gutter or groove, is equal paris; the gass to be examined was introsufficient for all private experiments.

duced into it, asier being properly dried, and the In order to acquire experiness in transferring tule is filled wiil mercury ai ile open end to a the gasses, it would be disable for the chemical given point; heat is then applied and thircilatastudent to begin his operations with common air, tion is observed by ihe quantity of mercury which by collecting andiransferring which licwould soon is pusled out. See Manchester Memoirs, vol. r. be qualities to manage any of the oiher gasses. Mr. Gay Lussar's apparaitrs is more complicated,, or other receiver, being filled with but equally prerjee; and as his experiments were water, and placed with its nouk dovanards over made on larger helhi of air, their coincidence with one of the holes in the shell of the trough, lei a those of Mr. Dalion adds considerably to ile conglass or other vessei be piumged into ihe water fidence which may be placed in the results. Tliesc will its mouth downwards; the air within the experiments are detailed, and the apparatus devesselwill preveni the entrance of the water; but scribed in Annal. rie Chin. Jiji. 187, they may if it be turned up the waier rushes in, and the air also be seen in Nicholson's Journal, V.S.vol.iii. rises in bubles to the surface: if this be done Still, liowever, though Gay Lussacfound the dilaunder the river, tie air will descend through iation to be from 100 to 137.5, boiveen and the hole, and rising in the upper part of the jar, 212° of Tahrenheit, the precise expansion for inwill there be detained, ande per part of the water crements of single degrees was by no means de: it coutains. Iltheair is io be transferred from a termined, nor does it appear yet to be attained

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with very desirable accuracy. An ingenious and ties of the gass, and the nature of the mixture, but simple method of doing this has been suggested are not sufficient to determine the proportions by Mr. Davy. See Nich. Jour. N. 8. iv. 32. and quantities of the several gasses of which it is Comp. with Thomson's Chemistry, i. 341. second composed. For this purpose all the methods of edition. See also EXPANSION.

analysis must be employed; and to direct these 1. Methods of separating the different gasses from properly, it is of great use to have a previous apeach other. As experiments often produce ewo, proximation by the above methods. Suppose, three, or more species of gass, it is necessary to be for instance, we know that the residuum consists able to separate these from each other, that we of oxygen and azotic gass mixed together, put a may ascertain the quantity and species of each. determinate quantity, as 100 parts, into a graduSuppose that under the jar, standing on the shelf ated tube, introduce a solution of sulphuret of of a pneumatic trough, is contained a quantity of potash, and leave it in contact with the gass; in different gasses mixed together, and standing over a few days the oxygen will be absorbed, and the mercury : we begin with marking with slips of azotic gass left pure. A more expeditious method paper the height at vhich the mercury stands is pointed out in the article Eudiometry. within the glass; and then introduce about a cu. If hydrogen gass be present, a quantity of the bical inch of water into the jar, which will swim gasseous mixture is introduced into Volta's Eu. over the surface of the mercury. If the mixture DIOMETER (see that word), along with a known of gass contains any muriatic or sulphuric acid proportion of oxygen gass; these are deflagrated giss

, a rapid and considerable absorption will together by means of the electrical spark; fresh instantly take place, from the strong tendency portions of oxygen gass are sụccessively added these two gasses have, especially the former, to fill deflagration ceases, and till the greatest possicombine with or be absorbed by water. If the ble diminution is produced. By this process wa. water produces only a slight absorption of gass, ter is formed, and is immediately united to the hardly equal to its own bulk, we conclude that the water of the apparatus; but if the hydrogen gass misture contains neither muriatic acid, sulphuric contain carbon, carbonic acid is formed at the acid, nor ammoniacal guss; but that it contains same time, which is not absorbed so quickly; the carbonic acid gass, of which water absorbs only quantity of this is readily ascertained by assisting about its own buik. To ascertain this conjecture, its absorption by agitation. If the mixture conintroduce some solution of caustic alkali, and the tain nitrous gass, by the addition of oxygen gass, carbonic acid will be gradually absorbed in the with which it combines into nitric acid, we can course of a few hours: it combines with the al- very nearly ascertain its quantity from the dimikali, and the remaining gass is left almost per- nution produced by this union. fectly free from any sensible residuum of carbonic These general remarks are made to convey an sod gass. After each experiment of this kind, we idea of this kind of investigation, and to shew the Dust carefully mark the height at which the mer- leading principles and rationale of the mode of cary stands within the jar, by slips of paper operation: it is not pretended that they will expasted on, and varnished over when dry, that plain every possible case, which would require a they may not be rubbed off when placed in the work of large and indefinite extent. A long expe*uer apparatus. It is likewise necessary to re- rience is necessary to become familiar with the gister the difference between the surface of the analysis of gasses. In many cases, from the diffmercury in the jar, and the height of the barometer culty of overcoming the strong affinities by which and thermometer.

several of the gasses

combined with When all the gass or gasses absorbable by water each other, and of determining when the separade absorbed, water is admitted into the jar to tion is complete, we must vary our experiments eplace the mercury; and the mercury in the in every possible point of view; adding new Ostern is covered with water to the depth of an agents to the combination, and keeping out inch or two.

After this, the jar is to be trans- ochers; and thus continuing our trials, till we Erted by the far dish before-mentioned, into the are certain of the truth and exactitude of our conwater apparatus; and the quantity of gass remain- clusion. ng is to be ascertained by changing it into a gra- To the foregoing observations on the means of duated jar. Small trials of it are then to be made separating the gasses, for which we are principalby experiments in litele jars, to ascertain nearly ly indebted to Lavoisier, we must add, that since the nature of the gass in question. For instance, the publication of that chemist's valuable eleinto a small jar full of the gass, a lighted taper mentary treatise, various instruments have been B introduced if the taper is not immediately contrived for attaining more readily and comextinguished, we conclude the gass to contain pletely the object of which we are treating, and ontgen gass, and in proportion to the brightness for receiving and retaining the gasses produced. of the tiame we may judge if it contain less or The earliest of these, which indeed was known to tute of oxygen ga-s than atmospheric air contains. Lavoisier, though he lived not to obtain a per

, on the contrary, the taper be instantly excin- fect set, was the celebrated apparatus of Woulfe, guished, we have strong reason to presume that a description of which may be seen under his ide residuum is chiefly composed of azotic gass Il, name. An improvell apparatus for preserving upon the approach of the taper, the gass takes fire separate the gasscous products evolved in many and burns quickly at the surface with a white processes was invented by Mr. Pepys, jun. and fame, we conclude it to be pure hydrogen gass; is represented in Pl. 78. fig. 1. A, the retort f this fame is blue, we judge it consists of carbon- joined to a cubulated receiver B. C, the adapter ated or carburetted hydrogen gass; and if it ground into the neck of the receiver, and furtakes fire with a sudden deflagration, that it is a nished with a glass valve made in the same manBoxcare of oxygen and hydrogen gass. lf, again, ner as those used in the improved Nooth’s appaupon mixing a portion of the residuum with oxy- ratus. D, Woulte's joined to the adapter to re17 gass red fumes are produced, we conclude ceive the unabsorbed gass; and E, a bent tube to that it contains nitrous gass. These preliminary carry the gass that may still pass unabsorbed either hatals give some general knowledge of the propers into a pneumatic apparatus, or into a chimney. VOL. V.



Fig. 2, the valve on a larger scale, and inserted be divided into cubical inches and tenths. The in the neck of the adapter. It consists of an in- bottle used for gauging these must hold seven oz. ternal tube of small calibre, but pretty stout in one dr. 15 grains of mercury, which exactly corsubstance, and ground into an exterior tube closed responds to a cubical inch of that metal. at the "pper end, but perforated with severai Thus prepared, let us suppose that, after an ex. small hole to allow the gass to pass. After the in- periment, there is a residuum of gass contained in ternal tube is ground to fit the external, a portion the upper part of the jar standing on the shelf of of it is cut out (as at a) suihicient to receive a a pneumatic apparatus, of which we wish to small hemisphere of glass, and to allow the hemi- ascertain the quantity; we must first mark the sphere to rise a little in its small chamber, but height to which the mercury or the water rises not to turn over in it. The upper piece of the in the jar with great exactness, by means of slips interna tube is then thrust home to the place in of paper pasted round the jar. If we have been which it is to remain, and the glass hemisphere operating in mercury, we begin by displacing the introduced, with its plane incumbent on the upper mercury from the jar, by introducing water in end of the lower piece of the internal tube, which its stead. This is readily done by filling a botue is ground perfectly flat, as is also the plane of the quite full of water, stopping it with the finger, hemisphere. From the construction, it is obvious turning it up, and introducing its mouth below that by the upwarii pressire of any gass, the glass the edge of the jar, then, turning down its body hemisphere may be raised so as to allow the aëri- again, the mercury by its gravity falls into the form fluid to pass into the adapter, but that there bottle, and the water, rising in the jar, takes the can be no return of any thing into the receiver, place occupied by the mercury. When this is even when a partial vacuuin takes place in it; and accomplished, pour so much water into the cisthe greater the excess of the expansive force or tern as will stand about an inch over the surface pressure exeried at any time in the adapter over of the mercury; then pass the dish B C (fig. 2. that maintained in the retort and receiver, the Pl. 77) under the jar, and carry it to the water ciscloser does the valve become.

tern already described. Here let the gass be transFig. 3, two adapters, A and B, ground to fit ferred into another jar graduated as above deinto each other, and also to fit into C of fig. 1. scribed, which will immediately shew its volume. Any number may be titted to each other in the Another method is to turn up the mouth into the same inanner. By this apparatus liquids may be marked jar, from which the gass has been libehighly impregnated with the gasseous products rated, as above, and then to pour in a smuch evolved during distillations. The bent tube T, is water as will reach exactly to the mark made for for the purpose of conveying the superabundant the gass ; by weighing the water carefully, the vogass to a chimney or to a pneumatic apparatus. lume of gass it contained before may easily be dePhil. Mag. vi. 256.

in termined, allowing at the rate of 1728 cubical · 6. Methods of measuring the volumes of gasses.--For inches for each 75-84 pounds troy of water. is this purpose we ought to be provided with several experiments where great accuracy is required, the graduated glasses or jars, of different sizes, and results obtained by these methods will need coreven several of each size, in case of accidents. rection; in the first, with respect to the height The manner of graduating recommended of the barometer and thermometer; and in the by Lavoisier and others, is very easy; care being second, beside the former correction, for the diftaken to secure accuracy, which is indispensable. ference between the surface of the water in the Take a tall narrow glass jar, and having filled it cistern, and the height to which it rises in the jar. with water, place it upon the shelf of the pneu- For the more expeditious and accurate admeasurematic cistern: we ought always to use the same ment of the volumes of gassts, various instruplace hroughout this operation, that the level of ments have been contrived, some of the principal the shelf may always be exactly similar, by which of which are described under the word GASalmost the only error to which this process is lia- OMETER, which is the general term applied to the ble will be av iided. Then take a narrow-mouth- apparatus. ed phial, holding exactly 5 ounces, 2 drams, 12 7. To delermine the absolute gravity of the differen! grains of water, which quantity corresponds to gusses. Take a large balloon A,Pl.79, fig. 4, capa. 10 cubical inches. If you have not one exactly of ble of holding 17 or 18 pints, or about half a cuthis capacity, choose one a little larger, and re- bical foot, having the brass cap bode, strongly ceduce it by dropping in a little melted wax and mented to its neck, and to which the tube and resin. This phual serves the purpose of a stand. stop-cock fg, is fixed by a tight screw. This apard for gauging the jars. Make the air contained paratus is connected by the double screw reprein this bottle pass into the jar, and mark exactly sented separately at fig. 6, to the jar B CD, ag. 4, the place to which the water has descended ; add which must be some pints larger in dimensions another measure of air, and again mark the place than the balloon. Tois jar is open at top, and is of water, and so on, till all the water be displaced. furnished with a brass cap hi, and the scop-cock It is of great consequence, that, during the course im. One of these stop-cocks is represented sepa. of this operation, the bottle and jar be kept at the rately at fig. 5. We first determine the eract casame temperature with the water in the cistern; pacity of the balloon, by filling it with water, and and for this reason, we must refrain as much as weighing it both full and empty. When empried possible from keeping the hands upon either, of water it is dried with a cloth introduced or, if we suspect they have been heated, we through its neck de, and the last remains of moismust cool them again by means of the water. ture are removed by exhausting it once or twice The height of the barometer and thermometer in an air-pump. When the weight of any gas is during this experiment is of no consequence. to be ascertained, this apparatus is used as fole When the marks have been thus ascertained upon lows: Pix the balloon A to the plate of an airthe jar for every ten cubical inches, we engrave a pump, by means of the screw of the stop-cock scale upon one of its sides, with a diamond pencil. g, which is left open; the balloon is to be el. In the same manner, glass tubes are graduated for hausted as completely as possible, observing careusing in the mercurial apparatus, only they must fully the degree of exhaustiva by means of the

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