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cate great strength, but add considerably to the symmetry of the horse, when viewed from behind. A horse well formed in the gaskins, is seldom badly shaped in the fore quarters; nor are such, in general, horses of inferior action; exclusive of which, they are necessarily free from the very awkward defect of cutting: an inconvenience of no small magnitude to a travelier with a weary horse upon a long journey. GASCONADE, a boast or vaunt of soniething very improbable. The term has its rise from the people of Gascony in France. See GASCONY.

GASCONY, a late province of France, bounded on the W. by the bay of Biscay, on the N. by Guienne, on the E. by Languedoc, and on the S. by the Pyrenees. The character of the inhabitants has been long that of a lively people, famous for boasting of their valour, which has occasioned the name of gasconade to be given to all bragging stories. This province, with Armagnac, now forms the department of Gers.

To GASH. v. a. (from hacher, French, to cut.) To cut deep so as to make a gaping wound.

GASH. S. (from the verb.) 1. A deep and wide wound (Spenser). 2. The mark of a wound (Arbuthnot).

GASHED LEAF. In botany. Folium incisum dissectum. Having the sections or divisions usually determinate in their number; or at least more so than in the laciniate leaf. The gashed differs from the cleft leaf (fissum), in having the sections extending but little beyond the edge (though deeper than in the crenate leaf); while in the cleft leaf they reach almost to the middle. See DISSECT and LA

CINIATE.

GA'SKINS. s. Wide hose; wide breeches (Shakspeare).

GASOLITRO, an instrument contrived by M. Goldschmidt, of Paris, to examine and measure the gasseous contents of mineral waters. This apparatus was designed, not only to expedite the process, but also to get rid of the trouble of using lime-water to detect the carbonic acid gass, and the inaccuracy resulting from its use, and from the variations of pressure in the common mercurial apparatus. In Pl. LXXVIII. A is a glass funnel to pour in the mercury into the glass cylinder C, which is graduated, shut by the cock B, and cemented on the plate D, made of delft-ware; E, wooden stand; F, stand to support the apparatus; G, glass tube, the cavity of which is about of an inch in diameter, and which communicates with the cylinder C, H, tube of the same diameter, communicating also with the cylinder C, and returning by an iron cock into the bottle J, intended to receive the mercury; K, cock for a double current of air; L, a matrass containing about four ounces of water, secured to the cock by a screw; M, sandbath; N, furnace; O, pump, the cylinder of which is glass, secured by two screws to the stand F; the use of this pump is to graduate the cylinder C; P, glass measure, to

contain a known quantity; Q, cock for a double current of air; R, bladder to contain the gass; S, cock; T, cock for a double current of air; U, glass pipe, coming from the cock T to K; Z, index of the second current of air. To know the quantity of gass which any gasseous water contains, we thus dispose the apparatus. Having shut the cock H, we fill the cylinder with mercury; we shut the cocks B and K, and open the cock A, to know the state of the apparatus; if it be in proper order, it will not make a vacuum in the cylinder C, further than the first mark; we fill the matrass up to the neck with the water we intend to analyse, and carefully fit the matrass to the cock K, by a screw provided with a little shield of leather: the whole being well secured, we open the cocks K and H, and heat the water to the boiling point. (Med. and Phys. Journal. English Encyclopedia).

To GASP. v. n. (from gape, Skinner.) 1. To open the mouth wide; to catch breath with labour (Addison). 2. To emit breath by opening the mouth convulsively (Dryden). 3. To long for (Spectator).

GASP. S. (from the verb.) 1. The act of opening the mouth to catch breath. 2. The short catch of breath in the last agonies (Addison).

GASS. (from the German, gheist; or the common Teutonic zart; from which root we obtain the terms ghost, ghostly, oghast.) An elastic aëriform fluid. It is written by the French, gaz, but improperly: it is also written by most Euglish writers, gas, yet, we think, improperly also, as an English word, since our established orthography duplicates in almost all monosyllables the in all, ball, call, in buff, cuff, stuff, and formerly, in terminating consonant, as in ass, pass, lass, gloss, winn, supp, &c.: In lack, sack, crack, &c. the dou

ble consonant is in like manner retained, the final k, having the power of a c: while in the term gass itself, every one spells it with a doubles in the plural, and writes, not gas-es, but gass-es.

This term was first used in chemistry by Van Helmont, who denoted by it the vapour of charcoal, (gass sylvestre) now known to be carbonic acid gass: he also applied it to other aërial fluids produced in his experiments; as gass fingue, extricated from inflammable substances during their their analysis by heat; gass flammeum, produced rit of life, &c. The air of the atmosphere he by the deflagration of nitre; gass vitiale, the spicalled gass ventosum. At present, gass is employed as a general term, to express all those aerial fluids, whether produced by chemical experiments or evolved in natural processes, which are not condensible by the cold of our atmosphere, and which differ from the air of the atmosphere: indeed, atmospheric air is a compound of three of the gasses, as will appear on referring to the articles AIR and ATMOSPHERE. The term gass does not include those aërial substances which arise from water, ether, and other fluids, on the appli speak of aqueous gass, etherial gass, &c.: these cation of heat, although Lavoisier, and others,

are now distinguished by the name of steam, or vapour, because they are easily condensed into their respective fluids again, merely by a certain reduction of temperature; whereas the gasses retain their elasticity in every variation of the temperature and pressure of the atmosphere.

gass.

Of these gasses there are now a considerable the muriatic acid gass, and the sulphuric acid number known: the principal of them are enumerated at the end of the articles AIR and CHEMISTRY; and will be found particularly described under their specific names.

1. History of discoveries relating to gasses. As these aerial fluids are so curious in themselves, and of so much importance in the economy of nature, and as the knowledge of them has contributed more, perbons, than any thing else to the advancement of chemical science, we trust we shall be justified, in the opinion of our readers, for pursuing the history of gasses to a greater extent than is usual in the introduction of our articles. In one sense, indeed, there will be an advantage in this measure; for we shall thus be enabled to bring together into one view a number of connected ob servations which must otherwise have been scattered in different parts of our work, and which, in such a state of dispersion, would have failed to present a distinct and comprehensive idea of the progress of discovery, relating to one of the most interesting branches of natural philosophy. In tracing the outlines of this history, we shall avail ourselves of many observations in an excellent paper in Tilloch's Philosophical Magazine, vol. 9. on the Chemical Knowledge which the Philosophers of the 16th and 17th Centuries had of the different Gasses.

If we pass over the remotest traces which occur bere and there in the works of the ancient writers, Van Helmont seems to stand at the head of those more acute philosophers, who distinguished these subtile fluids from the air of the atmosphere. For, though it cannot be denied, that he disfigured his valuable discoveries by numerous fictions, and concealed them under new and commonly barbarous names, which were for the most part improper, yet he first informed physicians and naturalists, and proved clearly by observations and experiments, that other fluids existed, which, though they approach very near to the air in subtilty, transparency, and particularly in elasticity, yet differ from it very much; and, as they differ also from vapours, he distinguished them by the particular name of gass, as above related. He was acquainted with the air of the celebrated Grotto dei Cane, near Naples, (see CARBONIC ACID), as well as with the exhalations in mines, against the pernicious effects of which cautions had been given long before his time by Andrew Libavius and George Agricola; and he knew also, that they killed animals which had purposely or accidentally been exposed to them, as well as imprudent persons, and particularly miners. He was in particular acquainted with that gass which some, because it inflames when it comes in contact with a burning body, call inflammable gass, and which others, because they consider it as an essential component part of water, name hydrogen gass; and he knew also that it had been observed before him in mines by Libavius: be convinced himself that even eructations were of the same nature, and that this gass formed a principal component part of smoke: he likewise considered flame to be only inflamed smoke, His knowledge, however, was not confined to this gass alone, for under the name of gass sylvestre he was acquainted with nitrous gass, produced by the action of aqua-fortis when silver is dissolved in it; and he knew also that when it came in contact with the atmosphere it formed fiery red vapours.

He appears to have been acquainted also with

He had become acquainted also, different ways, with that gass which shows itself in air in which various bodies, and particularly coals, have been burnt; and on that account he had given it the name of coal gass; though he had seen abundance of it in various places, and accompanying other phænomena, both in living human bodies, as for example in belching, and on a larger scale, as in wine and beer cellars, and during the effervescence of different substances when acids were poured upon them, in the Grotto del Cane and other subterraneous places; particularly in acid waters, from which it rises in bubbles, and they are indebted to it, he says, for all their healing qualities. He remarks also of this gass, that, as it extinguishes the flame of a lamp or taper, it extinguishes also the flame of life. He proved, that the volume as well as the goodness of air is lessened by bodies burning in it; for, having placed a burning taper under a glass in such a manner that it stood three inches above the water in the vessel, he saw the water rise, assume the place of the decreasing air, and at length extinguish the taper.

He had observed also, that an air could be produced from nitre, which he called flame gass, and which was disengaged on coal being added to it; and he thence conjectured the presence of vital air in that salt. He entertained also the opinion, which modern chemistry has supported by so many conclusive proofs, that all these air-like fluids are indebted for their form to the effects of fire, or, as we commonly say at present, to caloric.

It cannot, however, be denied, that Van Helmont considered as different gasses those which differ only by accidental corruption, as the carbonic acid gass, according as it is drawn from this or that body, and in this or that manner; and that he confounded others, or did not make a proper distinction between them. Yet before Priestley, most of the philosophers who paid attention to this subject made no other difference between these kinds of gass, than that some of them inflame when brought into contact with a burning body, while others instantly extinguish a flame.

Van Helmont suspected also the great similarity which, in regard to air, is found between flame and animal life. This was more clearly perceived by Thomas Willis and Francis Sylvius de la Boë, a man whom few have equalled in genius or eloquence.

This Sylvius proved nothing by experiments; but he made it probable, according to his manner, that sourish particles of nitre floated about in the common atmosphere, and approached so near to the prevailing principles of the present day, that he supposed fire (or caloric) was continually dif fused through the air.

The celebrated Spanish mineralogist Alphonso Barba was acquainted with those pernicious damps which arise so often in mines, and which, though they resemble air in other respects, have however an offensive smell, extinguish lights, and deprive men, birds, and even snakes, of their life.

Boyle, to whom natural philosophy in general is under so many obligations, though he erred in ascribing the increase of weight which metals acquire by calcination, rather from the fire than to particles from the atmosphere, was nevertheless acquainted with the carbonic acid gass as it rises

from coral, when it effervesces with vinegar, from bread, cherries, grapes, pears, apricots, plums, gooseberries, peas, &c. when they ferment, and its highly pernicious effects on animals; as also with the inflammable, as it partly occurs in abundance in many mines, for example, those of Hungary, partly as it arises by a solution of iron in diluted sulphuric acid or muriatic acid, and its property of inflaming when brought into contact with flame.

The latter as a highly pernicious kind of gass, abundant in coal-pits, is mentioned by Martin Lister, Jessop, and P. R. Moslyn; and a fire which took place in a coal-pit by the inflammation of such vapour is mentioned by Hodgson, in the Philosophical Transactions for 1676.; a like vapour was found about the same time by Beaumont in other subterranean holes; by T. Shirley above a spring, and Wolfstriegel and Vollgnad in a spring. Pope, in the first volume of the Philosophical Transactions, gave a very lively picture of that corrupted kind of gass in a hole near the Jake of Agnano; and L. A. Portius and Leonhard à Capua, that of Grotto del Cane, and other caverns in the neighbourhood of Naples; E. Hagendorn and F. Hoffmann, the dangerous quality of air in which coals have been burnt; and T. Birch, in 1668, that of air which has been corrupted by the breath of animals. S. Ledelius mentions the death of a person which took place in a cellar fill ed with wine in a state of fermentation. This gass, as it rises both from fermenting liquids as well as from lixivious salts and earths, when they efferresce with acids, and in which, even in his time, Bernoulli sought for the cause of this effervescing, was perfectly well known to sir Christopher Wren, in 1675. He relates a method by which such fluids can be collected and preserved in vessels; and he knew that the above gass is absorbed by water, and he distinguishes it very clearly from nitrous gass. Even the nitrous gass of the moderns seems to have been known to Huygens and Papin, for they relate, that they obtained such a fluid from the mixture of spirit of wine and spirit of nitre under the receiver of an air-pump.

At the same period, F. Slare and T. Willis ascribed the dark red colour of the blood to the air; and J. Mayow, another Englishman, with whom another Oxford physician, Henry Mand, and also Willis, L. M. Barbieri, and J. B. Giovanni, concurred, made the whole use of breathing to consist of this-that the lungs of animals inhale from the atmosphere nitrous particles, which are diffused over the animal spirits and communicate warmth to the blood. J. N. Pechlin, also, attributes the faculty of some divers being able to remain longer under water to a greater quantity of nitre. From all this, it appears, that the physicians of that period had a kind of idea of vital air, and its influence on the animal economy.

Stephen Hales, who made further progress by his numerous experiments in discovering the secrets of nature, placed beyond all doubt, by a long series of experiments, the elasticity of these fluids as they are expelled from bodies by heat, fermentation, corruption, and effervescence, a power which was before observed by Newton, and at the same time showed several and ingenious methods how they could be observed, preserved, measured, weighed, and even handled. He remarked the inflammability of those which the inflammable bodies of every kingdom of nature yield by exposure to a strong heat, the properties of

others which arise from effervescing mixtures, and which suddenly extinguish flame. He observed likewise, exceedingly well, the great difference of the nitrous gass which he obtained when he poured upon antimony aqua regia, or spirit of nitre; or the latter diluted with water (aqua-fortis) upon iron filings or quicksilver, and its property of forming red clouds with common air as soon as it comes in contact with it; and, by repeated experiments, that it absorbed a great portion of air; and also, that the oftener the experiment was repeated, the gass always absorbed the less air; that several of these gasses were absorbed by water; how much the best air is corrupted by the breathing of even the soundest men, so that at last it is totally unfit for respiration. He knew also the ammoniacal as well as the muriatic acid gass, and the sulphuric acid gass, and had learned, from his own experience, that the latter can be as strongly compressed as common air. He knew also that metals increase in weight by calcination, and again decrease on being revived; for he found that red lead in the preparation bad increased in weight about a twentieth part, and by a strong heat gave a great deal of air; his own experience had taught him also that phosphorus, sulphur, and a tallow candle, absorb some of the air in which they burn, as animals absorb some of the air in which they breathe; though he ascribed the pernicious change which the air thereby experiences, not to the loss it sustains, but rather to the corrupt evaporation with which it is filled. He had observed, though less perfectly, that phosphorus after combustion increased in weight by imbibing something from the atmosphere. He had discovered that an aëriform substance was contained in acidulous waters, and that air was continually absorbed by plants in a healthy state. See his Statical Essays, passim.

In this difficult doctrine, however, he left a great deal to be explained by his followers; for he did not define and was not acquainted with the difference of many of the gasses, and some of them escaped his notice altogether. The further illustration of them was reserved for the modern chemists. Thus, in particular, the following authors have very much contributed to enlarge our knowledge of the carbonic acid :-Dr. Black, in 1764; T. Henry, in 1773; the Dutch naturalist, D. De Smedt, in the same year; T. A. Emmer, in 1784. Among the Germans, N. C. Jacquin, iu 1769; and J. J. Well, in 1772. Among the Italiaus, Fontana, in 1774. In Switzerland, Sol. Schintz, in 1778, and in Sweden, sir Tobias Bergman. The last mentioned chemist shewed also, as did Brownrigg in England, and Venel in France, that acid waters are principally indebted to this substance for their properties; so that several chemical authors, such as Bergman, Rouelle, Duchanoy, Laugier, Meyer, and Kostlin, have described the process by which they can be exceedingly well imitated.

With the like care and ingenuity, the following writers have examined the nature of the inflammable kinds of gass: Lassone, in 1766; Volta, in 1777; Senebier, of Geneva, in 1784; Minkalers, of Lovain, in 1784; Kirwan, in 1786; Moscheni, of Lucca, in 1788; Gengembre, and Raymond, in 1791; Nieuwland, Deiman, Froostwyk, and Bondt, in 1792. The three last, together with Lauremburg, examined the different kinds of inflammable gass.

The dephlogisticated nitrous air of Dr. Priestley, now called nitrous gass, has been also examined

by Fontana, Bochaute, Deiman, Bondt, Nieuwland, Footswyk, &c. &c. Azotic gass was noticed by professor Schmidt in the first volume of Gren's Journal; Wieglib in Crell's Annals, in 1796; and a multitude of writers since. The inflammable muriatic acid gass was treated by Westrumb in Crell's Annals for 1790, &c.

But this new field in the province of natural knowledge has been cultivated in a more extensive manner, by a variety of authors, who have not confined their attention to one or two gasses, but have investigated with more or less precision and advantage all that they had an opportunity of examining. in Italy, Barbarigo, Fontana, Bucci, and Volta; in France, Berthollet, Bucquet, Corrinus de la Metherie, Rouland, Sigaud de la Fond, Thouvenel, Lavoisier, Fourcroy, &c.; in England, Keir, Plunket, Cavallo, Cavendish, Higgins, &c. &c.; in the Netherlands, Froostwyk and Deiman; in Germany, Achard, Herbert, Leonardi, Weber, &c. But among the philosophers who have explained and illustrated the nature of these gasses by numerous experiments, made with great care and accurately described, none have distinguished themselves more than Scheele and Dr. Priestley. The former a native of Germany, but settled in Sweden, invented very simple processes, yet well calculated to answer the proposed end, of examining these gasses, by which means he discovered new kinds, and proved the existence of those already known in a much clearer method than had been done before in his Abbandlung von der Luft and dem Feuer nebst einem Vorbericht von T. Bergman, Upsal and Leipsic, 1777, 8vo.; and in Kongl. Svensk. Vetenskap. Academn. Handling, 1774, p. 84. The latter, being furnished with a more extensive apparatus, placed in a clearer point of view not only the nature and differences of the gasses before discovered, but discovered new ones also. An account of his experiments may be seen in Experiments and Observations on the different Kinds of Air, London, 8vo. vol. i. 1774, vol. ii. 1775, vol. iii. 1777; Experiments and Observations relating to various Branches of Natural Philosophy, with a Continuation of Observations on Air, 8vo. vol. i. London, 1779, vol. ii. Birmingham, 1782, vol. iii. 1790; Directions for impregnating Water with fixed Air, &c. London, 1772, 8vo.; Philosophical Transactions of the American Society, 1796; and various other works within this period may be consulted with advantage.

In consequence of these researches, the nature of gasses in general became better understood, and their characteristic properties were ascertained with sufficient accuracy to point out and establish a clear distinction between the individual gasses. Hence, therefore, it is unnecessary to pursue our history farther in this place; for, though these interesting fluids have recently engaged, more universally than ever, the attention of philosophers, the discoveries which have been made respecting each will admit of a more convenient arrangement under the name of the particular gass to which they relate.

The gass arising from the distillation of coal has lately been applied, on a large scale, to the illumination of houses, manufactories, streets, &c.

2. Formation of gasses.-Every individual gass is supposed to be formed of two elements; the particular substance which gives name to the gass, and is called its basis-and caloric, by the expansive power of which it is made to assume the

gasseous form, and of which different proportions are required to combine with different substances. We are not able to set a limit to the number of bodies which may be made to assume this form, or to that of the various processes and combinations during which gasses are involved.

In order to reduce any substance to the state of gass, the application of caloric may be made in different ways. The most simple method consists in placing the body in contact with another body that is heated: in this situation, the caloric on one hand diminishes the affinity of aggregation or composition, by separating the constituent principles to a greater distance from each other; and on the other hand, the caloric unites with the principles to which it has the strongest affinity, and volatilizes them. This process is according to the method of simple affinities; for, in fact, it consists of the exhibition of a third body, which, presented to a compound, combines with one of its principles, and carries it off. The method of double affinity may also be used for the same purpose; as when we cause one body to act upon another to produce a combination, in which a disengagement of some gasseous principle takes place. If, for example, sulphuric acid be poured upon oxyd of manganese, the acid combines with the metal, while its caloric seizes the oxygen, and rises with it. This takes place, not only in the instance we have quoted, but on all other occasions wherein an operation being performed without the application of heat, there is a production of vapour or gass. The various states under which bodies present themselves to our eyes, depend almost entirely upon the different degrees of combination of caloric with these bodies: tiuids do not differ from solids, nor gasses from fluids, but because they possess such a quantity of caloric as is requisite to maintain them in one or the other state respectively. For the methods employed in preparing the different kinds of gass, we refer to their names.

3. Modes of collecting and transferring the gasses.It was not long after the discovery of the gasses, and the proof of their diversity, that methods were devised to manage them at pleasure. Dr. Priestley, the most successful, though not the earliest cultivator of this department of chemistry, the extension of which forms a most important era in the history of the science, was the first who effected a contrivance by which these singular fluids may be collected, retained, transferred from one vessel to another, and subjected to every variety of experi ment at the will of the operator. The principal article in the pneumatic apparatus is the trough, resorvoir, or cistern, which has been much improv. ed in point of convenience since it was first invented; though the principle of its construction is retained. The present form of this vessel is represented in fig. 1. Pl. 77. It may be made either of wood lined with leather, or of sheet iron, tinned, japanned, or painted: wood alone is not so proper, be cause if not kept full of water it will become leaky. A little below its brim a shelf AB is placed, about a half or third part as wide as the trough; in this shelf are several holes, each terminating a funnellike excavation, the widest part of which is on the under side of the shelf. The use of the shelf is to support receivers, jars, bell-glasses, or other vessels intended to contain the gass. To use the trough, so much water must be poured into it as is sufficient to cover the shelf to the depth of about an inch; and the receiver being filled with water

in the deep part, must be placed invertedly on the shelf, its open end turned down upon one of the holes; the gass then being conveyed to the under part of the excavation by means of a curved or other tube, or suffered to escape from its former vessel, will ascend through the hole into the receiver, displacing the water as the quantity of gass increases. This trough may be made of various sizes, according to the purpose for which it is intended: one of about two feet long, 16 inches wide, and 15 high, will be found sufficient for most experiments. Sometimes, however, a much larger one is necessary; and in laboratories, where a considerable number of experiments are performed, it is also requisite to have several smaller ones, which may be moved when necessary near a furnace, or wherever they may be wanted. Fig. 2. represents a jar, being filled with gass, standing in a dish containing water, and having two handles to transport the vessels from one cistern to another, or for keeping them in reserve when the cistern is too full.

A more commodious method of constructing the pneumatic trough is shewn in fig. 3.; where aa, is the well to contain the water for Gilling the vessels, &c.; bb, a small shelf with holes; and on a level with it the surface cc, covered also with water; and not more than two or three inches distant from the brim; dd, depressions, or hollows, to receive the curved necks of bottles, or the curved ends of tubes; ere, vessels invented on the surface of the trough; f, a large shelf underneath to contain vessels for use. Instead of a rectangular, some persons prefer a curvular, and others an oval shape for their troughs.

Some of the gasses are capable of being absorbed by water, and therefore cannot be collected by means of the above apparatus. When that is the case, mercury must be used; and on account of its gravity and dearness, a smaller trough, formed somewhat differently, must be employed; as represented in figs. 4. and 5., of which the first is a perspective view of the spherical cavity and groove to be filled, and something higher with mercury; the receiving vessel is likewise to be filled with that metal and inverted. Fig. 5. a section of the same, shewing the manner of placing the receiver, and the neck of the retort, or other vessel, from which the gass is to be supplied. The receiver ought to be of smaller diameter, and much stronger than when water is employed. A mercurial trough may be cut out of marble freestone, or a solid block of wood; but the first is preferable. A trough of about twelve inches long, three wide, and four deep, besides the gutter or groove, is sufficient for all private experiments.

In order to acquire expertness in transferring the gasses, it would be advisable for the chemical student to begin his operations with common air, by collecting and transferring which he would soon be qualified to manage any of the other gasses. The bell-glass, or other receiver, being filled with water, and placed with its mouth downwards over one of the holes in the shelf of the trough, let a glass or other vessel be plunged into the water with its mouth downwards; the air within the vessel will prevent the entrance of the water; but if it be turned up, the water rushes in, and the air rises in bubbles to the surface: if this be done under the receiver, the air will descend through the hole, and rising to the upper part of the jar, will there be detained, and expel part of the water it contains. If the air is to be transferred from a

vessel that is stopped like a bottle, it must be unstopped with its orifice downwards in the water, and then inclined in such a manner that its neck may come under the excavation of the shelf. The gass will escape from the bottle, and passing through the hole into the vessel intended to receive it, will ascend into the form of bubbles as before. Sometimes a bent glass tube, such as appears connected with the flask in fig. 7, is employed to conduct the gass under the water or mercury into the receiver. Some other methods occasionaily resorted to, particularly in collecting gasses for distillations, will be noticed in the article PNEUMATIC apparatus.

4. Dilation or expansion of gasses.-The influence of caloric, in dilating or expanding bodies, has been long known as a fact; though the laws by which this influence is regulated are not even now perfectly ascertained. In general it is observed that the expansion of bodies is greatest in their gasseous form, less in their fluid, and least in their solid state; as an example, it is known that the expansion of air is more than eight times greater than that of water, and that of water is about 45 times greater than that of iron. Many experiments have been made to ascertain the rate of expansion in gasses according to the elevation of temperature; but the results obtained were so various, on account chiefly of the want of sufficient care to exclude water from the vessels in which the expansion was measured, that for a long time no settled opinion could be formed on the subject. At length, however, the problem engaged the attention of two very ingenious and precise philosophers, whose experiments agree in furnishe ing a conclusion as curious as it was unexpected; namely, that the progress of dilatation is absolutely equal in all the different kinds of gass; or that all the different clastic fluids, taken at the same temperature, expand equally by heat: that all the different gasses, from the lightest to the heaviest, taken at temperature, are equally expanded by caloric. The experiments of Mr. Dalton were read to the philosophical society at Manchester, in October, 1801, and published in 1802: the dissertation of Gay Lussac did not appear in the Ann. de Chim. (vol. 43), till more than six months after: our own countryman must therefore be regarded as the original discoverer of this important law. Mr. Dalton's experiments are distinguished by a simplicity of apparatus which adds greatly to their value, as it puts it in the power of others to repeat them without difficulty. It consists merely of a glass tube, open at one ead, and divided into equal parts; the gass to be examined was introduced into it, after being properly dried, and the tube is filled with mercury at the open end to a given point; heat is then applied, and the dilatation is observed by the quantity of mercury which is pushed out. See Manchester Memoirs, vol. v. Mr. Gay Lussac's apparatus is more complicated, but equally precise; and as his experiments were made on larger bulks of air, their coincidence with those of Mr. Dalton adds considerably to the confidence which may be placed in the results. These experiments are detailed, and the apparatus described in Annal. de Chim. xliii. 187; they may also be seen in Nicholson's Journal, N. S. vol. iii. Still, however, though Gay Lussac found the dilatation to be from 100 to 137-5 between 32o and 212' of Fahrenheit, the precise expansion for increments of single degrees was by no means determined, nor does it appear yet to be attained

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