GASES.

As a point of historical interest, we may mention that many years before the publication of Faraday's earliest researches on this subject, sulphurous acid gas had been liquefied by Monge and Clouet, ammonia by Guyton Morveau, and arseniuretted hydrogen by Štromeyer, by the simple application of cold, without any increased pressure.

The expansion and contraction of gases by changes of temperature is treated of under HEAT.

The process of intermixture in gases, and the movements of these substances generally, have been very carefully studied by Faraday, Döbereiner, Mitchell, Bunsen, and especially Graham. These movements are usually considered under four heads, viz.: 1. Diffusion, or the intermixture of one gas with another; 2. Effusion, or the escape of a gas through a minute aperture in a thin plate into a vacuum; 3. Transpiration, or the passage of different gases through long capillary tubes into a rarefied atmosphere; 4. Osmosis, or the passage of gases through diaphragms.

In the article Diffusion (q. v.), the general principles of this kind of movement in gases are sufficiently explained, and we shall merely make one or two supplementary remarks, chiefly with the view of rendering the following table more intel

Hydrogen,

Gas.

ligible. Graham's experiments with the simple diffusion-tube shew (see Graham's Memoirs in the Transactions of the Royal Societies of London and Edinburgh, or Miller's Chemical Physics) that the diffusiveness or diffusion volume of a gas is in the inverse ratio of the square root of its density; consequently, the squares of the times of equal diffusion of the different gases are in the ratio of their specific gravities. Thus, the density of air being taken as the standard of comparison at 1, the square root of that density is 1, and its diffusion volume is also 1; the density of hydrogen is 0-0692, the square root of that density is 0-2632, and its diffusion volume is 2, or 3.7994; or, as actual experi ment shews, 383-that is to say. if hydrogen and common air be placed under circumstances favouring their mutual diffusion, 3.83 volumes of hydrogen will change place with 100 of air. The following table gives: 1. The density; 2. The square root of the density; 3. The calculated, and 4. The observed velocity of diffusion or diffusiveness of several important gases; the numbers in the last column, headed Rate of Effusion,' being the results obtained by experiment upon the rapidity with which the different gases escape into a vacuum through s minute aperture about of an inch in diameter.

Light Carburetted Hydrogen,

0.559

0.7476

1.3375

1.344

Carbonic Oxide,

0.9678

0.9837

1-0165

1.0149

1-935; of olefiant gas, 1980; and of hydrogen, 2-288. In the passage of gases through diaphragms, the law of the diffusion of gases is more or less disturbed or modified according to the force of adhesion in the material of which the diaphragm is composed; the disturbance being greatest in the case f soluble gases and a moist thin diaphragm, such as a bladder or a rabbit's stomach. For details or this subject we must, however, refer to the article OSMOSIS.

The process of diffusion,' says Professor Miller, | 1.369; of sulphuretted hydrogen, 1-614; of ammonia, is one which is continually performing an important part in the atmosphere around us. Accumulations of gases which are unfit for the support of animal and vegetable life are by its means silently and speedily dispersed, and this process thereby contriLutes largely to maintain that uniformity in the composition of the aerial ocean which is so essential to the comfort and health of the animal creation. Respiration itself, but for the process of diffusion, would fail of its appointed end, in rapidly renewing to the lungs a fresh supply of air, in place of that which has been rendered unfit for the support of life by the chemical changes which it has undergone.'

A reference to the last two columns of the above table shews that, within the limits of experimental errors, the rate of effusion of each gas coincides with its rate of diffusion.

Graham's experiments shew that the velocity of transpiration (the term which that chemist applied to the passage of gas through long capillary tubes) is entirely independent of the rate of diffusion, or of any other known property. It varies with the chemical nature of the gas, and is most probably 'the resultant of a kind of elasticity depending upon the absolute quantity of heat, latent as well as sensible, which different gases contain under the same volume; and therefore will be found to be connected more immediately with the specific heat than with any other property of gases.' Oxygen is found to have the lowest rate of transpiration. Taking its transpiration velocity at 1, that of air is 1.1074; of nitrogen, 1·141; of carbonic acid,

All gases are more or less soluble in water and other liquids. Some gases, as, for example, hydrochloric acid and ammonia, are absorbed by water very rapidly, and to a great extent, the liquid taking up 400 or 600 times its bulk of the gas; in other cases, as carbonic acid, water takes up its own volume of the gas; whilst in the case of nitrogen, oxygen, and hydrogen, it does not take up more than from to of its bulk. As the elasticity of the gas,' says Professor Miller, 'is the power which is here opposed to adhesion, and which at length limits the quantity dissolved, it is found that the solubility of each gas is greater, the lower the temperature, and the greater the pressure exerted upon the surface of the liquid. Dr Henry found that at any given temperature the volume of any gas which was absorbed was uniform, whatever might be the pressure; consequently, that the weight of any given gas absorbed by a given volume of any liquid at a fixed temperature, increased directly with the pres sure. If the pressure be uniform, the quantity of any given gas absorbed by a given liquid is also uniformn for each temperature; and the numerical

GASES.

taken up by water from the atmosphere, it is the means of maintaining the life of all aquatic animals If the air be expelled from water by boiling, and it be covered with a layer of oil, to prevent it from again absorbing air, fish or any aquatic animals placed in such water quickly perish. Even the life of the superior animals is dependent upon the solubility of oxygen in the fluid which moistens the air-tubes of the lungs, in consequence of which this gas is absorbed into the mass of the blood, and circulates through the pulmonary vessels.'

expression of the solubility of each gas in such bubbles. Small as is the quantity of oxygen thus liquids, is termed its coefficient of absorption or of olubility, at the particular temperature and pressure, the volume of the gas absorbed being in all cases calculated for 32 F., under a pressure of 29.92 inches of mercury. Thus, 1 volume of water at 32, and under a pressure of 29-92 inches of the barometer, dissolves 0-04114 of its volume of oxygen; and this fraction represents the coefficient of absorption of oxygen at that temperature and pressure. Similarly, the coefficient of absorption of common air is 00241. In consequence of this solubility of the air, all water contains a certain small proportion of it in solution; and if placed in a vessel under the air-purp, so 23 to remove the atmospheric pressure o its surface, the dissolved gases rise in minute

The following table, drawn up from the researches of Bunsen and Carius, shews the solubility of some of the most important gases, both in water and alcohol:

All these gases, with the exception of hydrochloric acid, may be expelled from the water by longcontinued boiling.

Gases are not absorbed by all liquids in the same order; for example, naphtha absorbs most olefiant gas, oil of lavender nost protoxide of nitrogen, olive oil most carbonic acid, and solution of chloride of potassium most carbonic oxide.

If a mixture of two or more gases be agitated with water, or probarly any other liquid, a portion of each gas will be absorbed, and the amount of each so absorbed or dissolved will be proportional to the relative volume of och gas multiplied with its coefficient of solubility at the observed temperature and pressure. As all ordinary liquids exert a greater or less solvent action on gases, a gas that we wish to examine quantitatively should be collected over mercury.

The adhesion of gases to solids next requires notice. Illustrations of this phenomenon perpetually occur. Thus, wood and other solid substances immersed in water or other liquids appear covered with air-bubbles. It is this adhesion of air to the surface of glass tubes which causes the difficulty of obtaining barometers and thermometers completely free from air. It is in consequence of the adhesion of air to their surfaces that many small insects are enabled to skim lightly over the surface of water which does not wet them. A simple method of illustrating this phenomenon is by gently dusting iron filings over the surface of a vessel of water; if we proceed carefully, a considerable mass of the iron may accumulate upon the surface; till, at last, it falls in large flakes, carrying down with it numerous bubbles of air. As the particles of iron are nearly sight times as heavy as water, it was only the adherent air that enabled them to float upon the surface. Closely allied to this adhesion is the remarkable property of condensation which porous bodies,

and especially charcoal, exert on gases. Owing to this property of charcoal-especially freshly burned vegetable charcoal-various gases may be separated from their watery solution by filtration of the latter through it; for example, sulphuretted hydrogen may be removed from water so completely that it cannot be detected either by its well-known odour or by the ordinary tests. Saussure found that 1 volume of freshly burned box-wood charcoal absorbed 90 volumes of ammonia, 85 of hydrochloric acid, 65 of sulphurous acid, 55 of sulphuretted hydrogen, 40 of protoxide of nitrogen, 35 of carbonic acid, 35 of bi-carburetted hydrogen, 94 of carbonic oxide, 92 of oxygen, 75 of nitrogen, 50 of carburetted hydrogen, and 17 of hydrogen. These results follow an order very nearly the same as that of the solubility of the gases in water.

Stenhouse has investigated the differences in the absorbent power of different kinds of charcoal; the following are his most important results: 05 of a gramme of each kind of charcoal being employed, and the numbers in the table indicating in cubio centimetres the quantity of absorbed gas.

GASKELL-GASSENDI.

hospitals, and in situations where putrescent animal u.atter is present, is found to act very beneficially in purifying the air by absorbing the offensive gases. Its use in reference to the filtration of water has been already alluded to.

The determination of the exact specific gravity of the different gases is of great importance in calculating the proportions of the different ingredients of compounds into which they enter; and the whole series of numbers expressing the chemical equivalents or atomic weights of bodies depend upon the accuracy of the determination of the specific gravity of hydrogen and oxygen.

The following table gives the specific gravity and the weight of 100 cubic inches of some of the most important gases at a barometric pressure of 30 inches, and at a temperature of 60°, together with

the name of the observer:

GRAVITY.

1857. Among her later works are Sylvia's Lovers and Cousin Phyllis. She died Nov. 12, 1865. GASOMETER. See GAS, LIGHTING BY. GASPÉ, the most easterly district of La wer Canada, consisting of the counties of Gaspe and Bonaventure, is chiefly a peninsula projecting into the Gulf of St Lawrence, between the estuary of the same name on the north and the Bay of Chaleur on 49° 20, and in W. long. between 64° 15′ and 67 the south. It stretches in N. lat. between 48° and 56', containing 7500 square miles, and about 14 000 inhabitants, the greater number being of French

descent. Cod and whale fisheries form the staple business of the country. The district is terminated towards the east by a cape of its own name, and this headland is the northern extremity of a bay also of the same name, which presents a safe and capacious harbour.

GASSENDI, or GASSEND, PIERRE, an eminent French philosopher and mathematician, was born 22d January 1592, at Champtercier, a little village of Provence, in the department of the Lower Alps. His unusual powers of mind shewed themselves at an early age; and in 1616 he became professor of theology at Aix. About this time, he drew upon himself the regards of Pieresc, whom Bayle calls the procureur-general of literature, and of Joseph Gautier, prior of La Valette, a distinguished mathematician, both of whom liberally gave him the benefit of their instructions and advice. With the first, he studied anatomy; from the second, he derived his taste for astron omical observations. After six years' study, he and undertook to maintain certain theses against became disgusted with the scholastic philosophy, the Aristotelians. His polemic appeared at Grenoble in 1624, and was entitled Exercitationes paradoxica

adversus Aristoteleos.

As to the chemical properties of gases, most of It was accompanied by an the different gases, when pure, can be readily expression of his belief in the church, for whose distinguished by some well-marked physical or shed the last drop of his blood.' He drew a dishonour and glory he declared himself 'ready to chemical property. Some are distinguished by their colour, others by their peculiar odour; but tinction for the first time between the church and several of the most important ones-viz., oxygen, must stand or fall by the latter. G. now visited the scholastic philosophy, denying that the former nitrogen, hydrogen, carbonic acid, carbonic oxide, Paris, where he made several influential friends light carburetted hydrogen, olefiant gas, and pro- In the same year in which he published his Exerci toxide of nitrogen-require other means for their discrimination. The distinctive characters of the tationes, he was appointed prevôt of the cathedral most important gases are noticed in the articles at Digne, an office which enabled him to pursue without distraction his astronomical and philoOXYGEN, HYDROGEN, CHLORINE, &c., and the out-sophical studies. In 1628 he travelled in Holland, lines of the general method of analysing a gaseous and got involved in a controversy with Robert mixture are given in a separate article. For further details on the physical and chemical characters of Fludd, an English mystic, relative to the Mosaic the gases, we must refer to Miller's Elements of Chemistry, and especially to the volume on Chemical Physics, from which we have borrowed freely; to Kekule's Lehrbuch der Organischen Chemie, 1859; and to Roscoe's translation of Bunsen's Gasometry.

GASKELL, MRS ELIZABETH C., an English authoress, was born about the year 1829, and was the wife of a Unitarian clergyman in Manchester. Her maiden name was Stevenson. Her novels, of which Mary Barton (1848) and Ruth (1853) are perhaps the best examples, are chiefly descriptive of the habits, thoughts, privations, and struggles of the industrial poor, as these are to be found in such a social beehive as the city in which the authoress resides. Some of her characters are drawn with remarkable dramatic power, and many of her descriptive pasBages are very graphic. Among her other works may be mentioned The Moorland Cottage (1850), a Christmas story; North and South (1855); Cranford; and Lizzie Leigh-the last three of which originally appeared in Household Words. Mrs G. also edited a very interesting life of Charlotte Bronte (q. v.),

cosmogony, in which he is admitted to have had greatly the advantage of his incoherent opponent. At the recommendation of the Archbishop of Lyon, a brother of Cardinal Richelieu, G. was appointed professor of mathematics in the College Royal de France, at Paris, where he died, 14th October 1655. As a philosopher, G. maintained, with great learning and ingenuity, most, though not all, of the doctrines of Epicurus, these being most easily brought into harmony with his own scientific acquirements and modes of thought. His philosophy was in such repute, that the savans of that time were divided into Cartesians and Gassendists. The two chiefs themselves always entertained the highest respect for each other, and were at one time on the friendliest terms. The agreeableness of their intercourse, however, was for a while interrupted by the publication of a work of G.'s, entitled Dubitationes ad Meditationes Cartesii, in which he expressed himself dissatisfied with the tendencies of the new system of philosophy introduced by Descartes, for G. was averse to novelty in the sphere of mental speculation, although he

GASSNER GASTEROPODA.

warmly espoused the side of progress in physical science and made himself many enemies among his bigoted ecclesiastical brethren for the love he bore it. He ranked Kepler and Galileo among his friends, and was himself the instructor of Molière. His principal work is entitled De vita, moribus et doctrina Epicuri (Lyon, 1647), to which the Syntagma Philosophie Epicurea (1649) belongs. It contains A complete view of the system of Epicurus. His Institutio Astronomica (1645) is a clear and connected representation of the state of the science in his own day; in his Tychonis Brahai, Nicolai Copernici, Georgii Peur bachii et Joannis Regeomonani Astronomorum Celebrium Vitæ (Par. 1654), he not only gives a masterly account of the lives of these men, but likewise a complete history of astronomy down to his own time. G. was pronounced by Bayle the greatest philosopher among scholars, and the greatest scholar among philosophers. His works were collected and published by Montmor and Sorbière (Lyon, 6 vols. 1658).

GASSNER, JOHANN JOSEPHI, a man who made a

with sulphuric acid, it is freed from its organic bases, and after further rectification, highly rectified naph tha,' or 'benzole,' is obtained. This is chiefly a mix ture of five oily hydrocarbons, which boil at various degrees, of which Benzene (CH) is the most volatile, boiling at 80.4°, and Cymene (C10H14) the least, boiling at 177.5°. Coal-tar naptha or benzole is largely used as a solvent for caoutchouc, and is also burned to produce a fine carbon for printing ink. Aniline is one of the products obtained from benzene, and within the last 12 years has acquired great industrial importance. and is now manufactured in enormous quantities on account of the splendid dyes which it is capable of yielding, of which the beautiful mauve and magenta are examples. The dead oil or heavy oil contains a considerable quantity of coal-tar creosote, or carbolic acid (C6H6O), and forms an excellent preservative for wood in damp places. It is also consumed in common lamps, but is chiefly used in making lamp-black. The pitch is much employed for making asphalt pavement, and in the preparation of roofing felt and roofing papers used in gravel roofing.

From the last portion of the distillation of the crude naphtha, and the first of the dead oil, a beautiful white crystalline solid, called naphthaline, is obtained. It has long been known without being applied to any useful purpose, the numerous efforts to employ it for the manufacture of colours not having proved successful. The dead oil also contains considerable quantities of a yellow solid termed paranapthaline, which is a mere chemical curiosity.

noise as an exorcist in the 18th c., was born 28th August 1727, at Bratz, near Pludenz, in the Tyrol, and became Catholic priest at Klösterle, in the diocese of Coire. While in that office, the accounts of demoniacs in the New Testament, combined with the writings of celebrated magicians, brought him to the conviction that most diseases are attributable to evil spirits, whose power can be destroyed only by conjuration and prayer. He began to carry out his conviction by practising on some of his distillates that pass over between 150° and 200° by The carbolic acid (CHO) is prepared from the parishioners, and succeeded so far as to attract notice at least. The Bishop of Constance called him mixing with potash ley and pulverized hydrate of to his residence, but having come very soon to the potassium, which converts the whole into a white crysconviction that he was a charlatan, advised him to talline magia. This is dissolved in hot water, the return to his parsonage. G. betook himself, how-rising oil removed, the alkaline liquid neutralized with ever, to other prelates of the empire, some of whom believed that his cures were miraculous. In 1774, he even received a call from the bishop at Ratisbon, to Ellwangen, where, by the mere word of command, Cesset (Give over), he cured who persons pretended to be lame or blind, but especially those afflicted with convulsions and epilepsy, who were all supposed to be possessed by the devil. Although an official person kept a continued record of his cures, in which the most extraordinary things were testified, yet it was found only too soon that G. very often made persons in health play the part of those in sickness, and that his cures of real sufferers were successful only so long as their imagination remained heated by the persuasions of the conjuror. Intelligent men raised their voice against him, and he lost all respect before his death. He died, March 1779, in possession of the wealthy deanery of Benndorf.

GAS-TAR, or COAL-TAR, a thick, black, opaque liquid, which comes over and condenses in the pipes when gas is distilled from coal. It is slightly heavier than water, and has a strong, disagreeable odour. Coal-tar is a mixture of many distinct liquid and solid substances, and the Beparation of the more useful of these constitutes an important branch of manufacturing chemistry. The tar is first distilled in malleable iron stills, when the more volatile portion called light oil or coal naphtha, consisting mainly of hydrocarbons of the benzene series, and a number of bases, passes over. The less volatile oil, or dead oil of coal-tar, contains phenol and carbolic acid, or coal-tar creosote (CHO), and several hydrocarbons of high boiling point, which exist at ordinary temperatures as crystalline solids. The residue left after repeated distillation is called pitch or asphalt, which also contains solid hydrocarbons and resinous compounds. By agitating the coal naphtha

hydrochloric acid, and the impure hydrate of phenyl (carbolic acid), which rises to the surface as an oil, is washed with water, digested over chloride of calcium, rectified several times, and gradually cooled to -10° in a closed vessel, when crystals of pure carbolic acid are separated.

Sulphuric acid extracts from the crude naphtha several volatile basic oils besides benzene, namely, toluene, xylene, cumene, and cymene, which are almost unknown in the arts, although they may yet come to be of great service. From the bases combined with it, aniline and sundry other compounds containing nitrogen may be obtained. There also occurs a curious body named pyrrol, the vapour of which gives to fir wood, dipped in muriatic acid, a splendid violet colour. Parafin, a colourless crystalline fatty substance, sometimes found in a solid state in bituminous strata, and known as fossil wax, is another product of coal tar.

GASTERO'PODA (Gr. belly-footed), or GASTROPODS, a class of molluscs, inferior in organisation to cephalopods, but far superior to almost all other molluscs, and containing a multitude of species, the greater number of which are marine, but some are inhabitants of fresh water, and some are terres. trial. Snails, whelks, periwinkles, limpets, cowries, and the greater number of molluscs with univalve shells belong to this class, and univalve molluscs constitute the greater part of it; but it contains also some molluscs with multivalve shells, as chitons, and some, as slugs, which have either only a rudimental internal shell, or no shell at all. Some aquatic kinds are destitute of shell in the adult state, but they are protected by a rudimentary shell on first issuing from the egg. No known gastropod has a bivalve shell, unless the operculum, which closes the mouth of the shell in many species, be regarded as a second valve.

Gastropods have a head, more or less fully developed, in which is situated the mouth, and

GASTEROPODA.