On molecular and microscopic science

Preface

Microscopic investigation of organic and inorganic matter is so pectiliarly ch.a^'acteristic of tlie actual state of science, that tlie Author has ventured to give a sketch of some of the most prominent discoveries in the life and structure of the lower vegetable and marine animals in addition to a few of those regarding inert matter.

The Author feels bound to return her best thanks to kind friends — Sir John Herschel, Mr. Huggins, Mr. Gwyn Jeffrey, Prof. Tyndall, and Mr. T. Moore, of Chelsea, who have aided in revising some of the sheets for press, and have thus counteracted the disadvantage under which she labours, of a residence abroad, and at a distance from libraries of reference.

THE

Contents

OF

F I E S T VOLUME.

PAET I.

ATOMS AND MOLECULES OF MATTEE.

SECT. PAGE

II. On Force, And Tiie Relations Between Force And

MATTER , .- .

m.

ATOMIC THEORY, ANALYSIS AND SYNTHESIS OF MATTEE,

UTILITY OF WASTE SUBSTANCES — COAX-TAR COLOURS,

ETC.

IT.

THE SOLAR SPECTRUM, SPECTRUM ANALYSIS, SPECTRA

OF GASES AND VOLATILIZED MATTER, INVERSION OF

COLOURED LINES, CONSTITUTION OF SUN AND STARS .

. PART II.

VEGETABLE OKGANISMS.

I,

MICROSCOPIC STRUCTURE OF THE VEGETABLE WORLD

II.

IV. ■ Lichens

T.

viii CONTJ^NTS OF THE FIRST VOLUME.

SECT. PAGE

Vir. MUSCI, OR MOSSES ' . . 323

VIII. EILICES, OR FERNS 335

IS. EaUISETACEiE, OR HORSETAILS 3G7

X. MAESnEACEiB, OR RHIZOSPERMiE 371

XI. LTCOPODIACEiE, OR CLttB MOSSES '. . . . . 373

XII. GENERAL STRUCTURE OE FLOWERING PLANTS . . 378

XIII. MONOCOTTLEBONOUS, OR ENDOGENOUS PLANTS . . 383

Xiy. DICOTYLEDONOUS, OR EXOGENOUS PLANTS , . , 404

ILLUSTRATIONS

TO

THE FIRST VOLUME.

(Mc Author is indebted to the works of Dr. Carpenter, Rev. M. J. Berkeley, Mr. Gosse, and Mr. Darwin, for the larger part of these Illustrations.)

FIG.

Eucyrtidium cranoides ....

PAGE

. frontispiece

Form of stratified dischiirge in a vacuum tube .

Form of stratified discharge in a vacuum tube, as

affected by an

electro-magnet .....

. 81

Development of Ulva ....

. 171

Vertical section of the cuticle of Iris germanica .

. 173

Longitudinal section of stem of Italian reed

. 176

Palmogloea macrococca ....

. 182

Protococeus pluvialis ....

,184

Volvox globator .....

. 189

Various species of Staurastrum .

'. 192

Economy of Closterium Lunula .

. 193

. 197

Biddulphia pulchella ....

. 198

Pleurosigma angulatum ....

, 199

U.

Actinocyelus imdulatus ....

. 200

Meridion circulare ....

. .201

Bacillaria paradoxa ....

, 203

Cell multiplication in Conferva glonierata

. 207

Zoospores .....

. 208

Threads of Eirularla nitida

, 21.3

Trichodesmium erythraeum

. 216

Conjugation of Zygnema quininum

. 217

Ulva latissima .....

. 22.')

Polyidos rotundas and Furcellaria fastigiata

. 229

X

ILLUSTRATIONS TO

24. Vertical sectious of conceptacles of Gracilaria armata, Grinnelia

• americana, and Corallina officinalis .... 230

25. Callitliamnion corymbosum . . . . . 232

26. Ehabdonia Coulteri, Sphserococcus corofnopifolius, 'Wrangelia

penicillata, and Cruoria pellita .... 236

27. Dictyiu'us purpurascens . ..... 242

28. Polyzonia cuneifolia ...... 243

29. Fruit of various species of Ectocarpus .... 245

30. Dictyota dichotoma ...... 247

31. Vertical section of receptacle of Fucus platycarpus . , 254

32. Various species of Puccinisei ..... 276

33. Puccinia G-raminis ...... 280

34. Various species of Mucedines ..... 286

35. Torula Cerevisiae, sliowing successive stages of cell-multiplication 287

36. Various species of Sphseriacei . . . . . 294

37. Various species of Lichens . . . . . 299

40. NiteUa flexilis . . . . . . .302

41. Antheridia of Chara fragiUs . . . . .314

42. Further doTelopment of antheridia of Chara fragilis . .315

43. Marchantia polymorpha . . . . . .317

44. Anatomy of frond of Marchantia poljmorpha . . .318

45. Archegonia of Marchantia polymorpha . . . .319

46. Elater and spores of Marchantia ..... 319

47. Funaria hygrometrica ■ , . ■ . . . . 324

48. Polytrichum commune, group of antheridia . . . 325

49. Polytrichiun commune, development of spermatozoids , . 325

60. Microscopic structure of loaves of mosses . . . . 330

61. Development of spores of Pteris serrulata . . . 336 .52. Antheridium and spermatozoids of Pteris serrulata . . 338.

63. Archegonium of Pteris serrulata ..... 338

64. Section of footstalk of fern frond . . . . .341

65. Pinnule of Polypodium bearing sori . . . . 342 56. Sporangia of Polypodiaceous ferns .... 343 67. Pinnule of Lastrea Filix-mas with sori .... 346 58. Sorus and indusium of Polystichimi or AspicKum . . . 347 69. Pinna of Polystichum Lonchitis . . . . . 348

60. Sorus and cup-shaped indusium of Deparia prolifera . 350

61. Seolopondriuni vulgare . . . . . . 351

62. Athyrium Filix-focmina ...... 353

63. Asplenium Ruta-muraria ...... 353

THE FIRST VOLUME. xi

FIG. PA^'^

64. Ceterach offieinarum . . . ■ • • 355

65. Blechnum Spicant . . . • • • .357

66. Pteris aquilina 357

67. Adiantiim Capillus-Veneris ..... 369

68. Trichomaues radicaus ...... 36_1

69. Hymenophyllum tunbridgense . . . . • 362

70. Equisetiim giganteum ...... 368

71. PiMaria miuuta ....... 371

72. Orchis mascula, side view of flower .... 389

73. Orchis mascula, front ■\-iew of flower . . . . 390

74. Orchis mascula, pollinium ..... 391

75. Orchis mascula, pollen grains ..... 391

76. Orchis mascula, poUinia ...... 392

77. Orchis pyramidalis, front view of flower .... 393

78. Orchis j^yramidalis, side view of flower .... 394

79. Orchis pyramidalis, disc with one pollinium . . . 395

80. Orchis pyramidalis, pollinia, attached to disc . . .395

81. Orchis pyramidalis, pollinia, with disc contracted . . 395

82. Orchis pyramidalis, pollinia, withdrawn .... 395

83. Epipactis palustris, side views of flower .... 397

84. Epipactis palustris, side view and dissection of flower . . 398

85. Listera ovata, side view of flower ..... 399

Errata.

Page 3, line 5 from bottom, insert the before earth * 69, line 19, dele the 69, line 21, dele the

69, lines 20 ancZ 22, for part rea<? parts

100. In the Table of Atomic Weights, read Copper 32; Zinc 32'5 ;

Rubidium 86 ; Caesium 1 33

101, lines 10 and SS,for 32 read 32^ 104, line 12 from bottom, for 29 read 32

MOLECULAR AND MICROSCOPIC SCIENCE.

PAET I.

ATOMS AND MOLECULES OF MATTER.

Section 1. Elementary Constittttiojt Of Matter

The investigations whicli have revealed the most refined and wonderful relations between light, heat, electricity, and highly elastic media ; the relation of these powers to the particles of solid and liquid matter, new methods of analysis, and the microscopic examination of that marvellous creation, animal and vegetable, which is invisible to the unaided eye of man, have brought a new accession to the indefinitely small within the limits of modern science.

Wherever the astronomer has penetrated into the depths of space, luminous points are visible ; and since light merely consists in the undulations of the ethereal medium, matter must exist in every part of the universe of which man is cognizant, for although the luminiferons ether is so attenuated that its very existence is almost an hypothesis, its atoms are not more inconceivably small than those of highly elastic ponderable matter on earth. Atoms are the ultimate constituents

VOL. I. *B

ATOMS AND MOLECULES OF MATTER, pakt i.

of homogeneous simple substances; molecules, or groups of heterogeneous atoms united in definite proportions, constitute such as are compound. High pressure steam is invisible as it issues from the boiler, yet each of its molecules contains two atoms of hydrogen and one of oxygen. The perfume of a flower is a compound invisible substance formed of molecules.

We laiow nothing of the forms either of atoms or of those groups of atoms which we call molecules ; but we cannot suppose them otherwise than as excessively hard, since conceive them how we will, we are sure that an atom, whatever be its form or nature, is ever the same. It never wears, it never changes, though it may have formed part of thousands of bodies and entered into thousands of combinations, organic and inorganic ; when set free by their dissolution, it is ready to enter into a new series ; it is indestructible even by fire, the same now as when created. Nor has the quantity of matter in our terrestrial abode ever been increased or diminished ; liable to perpetual change of place and combination, the amount remains the same : the bed of the seas may be changed to diy land, and the ocean may again cover the lofty mountains, but the absolute quantity of matter changes not.

All substances, whether solid, liquid, or aeriform, are supposed to consist of hard separate atoms or particles, and in conformity with that suj)position to be surrounded by the ethereal medium, othenvise they could not transmit light and heat, which are merely vibrations of that medium. Even the hardest and most compact substances are capable of compression, and have been compressed to an enormous degi'ee by the hydi-a\ilic press ; but it probably transcends mechanical force to bring their atoms into contact : in fact, no known substance is impervious to both light and heat, however thin.

By far the greater number of terrestrial substances consist of heterogeneous atoms chemically combined

•. I. METALS AND THEIR PROPERTIES.

into atomic systems or molecules ; but there are sixty-four wliicli have never yielded to chemical analysis, and are therefore believed to be respectively formed of only one kind of atoms. Thirty-five of these are metals found either pure or as ores, and sixteen are metals existing naturally in chemical combination with alkalies, alkaline earths, or earthy bases, that is as salts, from which they have been obtained by the analytical power of electricity or other means. The thirteen remaining simple substances are non-metallic : some are aeriform, some solid, one liquid.

The alkaline metals are sodium, potassium, lithium, CEBsium, rubidium, and thalHum. They are distinguished by their energetic , affinities for, and the simplicity of their compounds with, non-metallic elements. They are never met with native, and are amongst the most diificult metals to reduce from their ores, and their spectra are remarkable for simplicity. Sodium and potassium — which have been such important agents in spectrum science — were reduced from their alkalies of soda and potash by Sir Humphry Davy by means of the voltaic battery, a discovery which led the way to the reduction of many of the others. Lithium is a white metal which burns brilliantly in air and oxygen; it swims in naphtha, and is the lightest solid body known. Caesium is the most energetic of all metals in its chemical affinities.

The metals of the alkaline earths are barium, strontium, calcium, and magnesium. They possess, like the precedmg, energetic affinities for the non-metallic elements, and are reduced with difficulty from their ores. Barium is obtained from earth baryta : it is powerfully alkaline, and its salts are colourless and poisonous. Calcium is obtaiiied from limestone, chalk, marble, and gypsum, which are amongst the most abundant constituents in the crust of the earth ; it is a bright ductile

B 2

METALS AND THEIR PROPERTIES. paet i.

metal of a bronze colour. Magnesium, which is a brilliant silver-white hard brittle metal, is obtained from magnesium limestone or dolomite. Although the ores of calcium and magnesium cover ~ vast areas of the globe, the metals form a very small comparative proportion of them.

The metals derived from non-alkaline earths are glucinum, yttrium, thormum, zirconium, and aluminium, which is the only one of any interest : it is now becoming a very usefal metal. It combines readily with oxygen to form clay. The ruby, sapphire, and oriental topaz are merely coloured varieties of corundum, which is nothing but crystallised clay. Rubidium, caesium, and thallium were discovered by spectrum analysis.

The avidity of some of these metals for oxygen .is quite remarkable : potassimn and rubidium inflame when they touch ice or cold water ; they decompose the water and combine with its oxygen. Calcium becomes luminous in warm water, and burns with intense Kght when heated to redness ; but a magnesium wii'e bums with such intense brilliancy that it has been employed for photography, and will probably become useful for hoxisehold purposes, as two ounces and a half of magnesium wire when burnt give a light equal to that of twenty pounds' weight of stearine candles.

The metals whose oxides are not reducible by heat without the aid of some form of carbon include nearly all the useful metals. They are all polyatomic, that is, they combine with other elements in the number of atoms varying from two to eight, and are di^dded into seven groups in regard to this propei-ty. For instance, zinc, copper, and cadmium are diatomic. Zinc is invaluable as a soui-ce of electric light aud heat in the voltaic battery, and its vapour burns brilliantly. Copper is one of the most useful of metals, while cadmium is of no value at ail. Nickel, cobalt, and uranium

SECT. I. METALS AND THEIR PROPERTIES. . 5 form the triatomic group ; tliey are remarkable for their complex spectra. Nickel is usually an ingredient in meteorites; cobalt is employed in pigments and in sympathetic inks ; and the oxide of uranium is \ised to stain glass, and gives it some very peculiar properties, as wiU.,be shown. The precious metals have a feeble affinity for oxygen at any temperature, and their oxides are decomposed by heat alone, and sometimes even by the undulations of light.

Metals are excellent conductors of heat, but they vary exceedingly in that respect ; both theory and experiment prove that the best conductors are invariably the vrorst radiators. In fact those atoms which transfer the greatest amount of motion to the ethereal medium, that is, which radiate most powerfully, are the least competent to communicate motion to each other, that is, to conduct with faciUty. Silver and copper are the best conductors of heat, but the worst radiators. These two metals are the best conductors of electricity, but it is influenced by temperature ; for MM. Matthiessen and Von Bose's experiments have proved that all x^ure metals in a solid state vary in conducting power to the same extent between zero and 100° Cent., and that the alkaline metals conduct electricity better when heated than when cold.

All metals are capable of being vaporized, but at very different degrees of temperature. Platinum reqviires the heat of the oxy-hydrogen blowpipe, which by estimation amounts to 8801° Cent. This property makes it valuable for terminal points to the conducting wires of the voltaic battery and magneto-electric induction machine where great heat can be employed without fusing the platinum terminals. Copper is always employed for the conducting wire on account of its superior conductive power. The coil of wire in the magneto-electric machine, which is often miles long, is insulated

OXYGEN.

Part I

by a coating generally of green silk thread. But in experiments of extreme delicacy where magnetism might vitiate the results, j)erfectly pure copper wire which is diamagnetic is used for the conducting wires in the thermo-electric pile of the goniometer, and the wires are coated with white silk thread, since it was discovered that the green dye contains some magnetic metal.

The mass of the metals however constitutes comparatively but a small part of the terrestrial globe, which is formed of chemical combinations of only thirteen simple elementary substances, — a wonderful manifestation of creative power that could form a world of such variety and beauty by means of atoms so little , diversified ; still more wonderful is it that four simple elements alone constitute the basis of nearly the whole organic fabric. The air we breathe, watei', the bodies of men and living creatures, and the vegetation that adorns the earth, are chiefly combinations of three invisible gases, oxygen, hydrogen and nitrogen, with carbon, the purest amorphous form of coal.

Oxygen gas forms three-fourths of the superficial crust of the terrestrial globe, its productions and its inhabitants. At least a third part of the solid crust of the earth is oxygen in combination ; it constitutes eight parts out of nine in water, and water covers three-fourths of the surface of the globe ; it forms more than twenty parts out of a hundred of atmospheric air, and in the organic kingdom it is an essential constituent. Except in the atmosphere, oxj^gen is never uncombined, but may be obtained by distilling chlorate of potash, by the decomposition of water by voltaic electricity, and by other means. When pure it is a colourless, tasteless, inodorous, invisible gas ; it is incombustible at ordinary temperatures, yet absolutely essential to combustion ; no animal can live long in it, and none can exist without it. In the atmosphere oxygen is highly magnetic ;

OZONE.

its magnetism increases with cold and decreases with heat; hence its intensity varies with night and day, winter and summer, but its magnetic property vanishes when it enters into composition.

Oxygen is perfectly quiescent and passive as a gas in the atmosphere, and as a constituent of water and sohd bodies, yet that inactivity conceals the most intense energy, which only requires to be called into action. Thus combustion of extreme intensity takes place when ignited sulphur is put into a vessel containing oxygen gas ; the metal potassium is instantly inflamed by it on touching water ; some of its combinations with chlorine are highly explosive, and phosphorus bui'ns iii it with dazzling splendour. Thus a stupendous amount of energy is latent in oxygen under the most tranqiiil appearance.

M, Schonbein of Basle discovered that oxygen exists in another state, which has neither the extreme quiescence on the one hand, nor the intense violence on the other, of its ordinary form ; and to express that intermediate condition, in which its activity is less in amount and different in quality, it has been called by another name, viz. ozone, from the following peculiarity.

It had long been observed that there is a peculiar smell when an electric machine is in activity, and when objects are struck by lightning ; that smell Professor Schonbein ascertained to arise from the change of" oxygen into ozone, and actually produced ozone by passing electric sparks through that gas. Ozone differs from oxygen ia having a strong smell and powerful bleaching property ; it piirifies tainted air, changes vegetable colours, and stains starch prepared by iodide of potassium blue, which thus becomes a test of its presencQ ; yet it certainly is oxygen in an allotropic or chan ged state, for it readily oxidizes or rusts silver and other metals, and when ozonized gas is sent through a red-

OZONE AND ANTOZONE.

PAET I.

hot tube, it comes out'pure oxygen. According to the experiments of Messrs. Tait and Andrews, oxygen gas loses six eighths of its volume, and becomes. four times moi'e dense by the change ; it contracts -more readily with obscure electricity than with the spark. The experiments of Professor Tyndall on the absorptionof radiant heat by gases give reason to believe that ozone is produced by the packing of the atoms of elementary oxygen into oscillating groups, and that heating dissolves the bond of union and restores the ozone to the form of oxygen. Ozone chiefly exists in air that has passed over a great expanse of sea, and the quantity is increased during the aurora, which alone might lead to a surmise of that phenomenon being electric.

The change of oxygen into ozone is not the only instance of Allotropism, — that is to say, the existence of the same substance in two states differing from each other in every respect, — for ozone itself is allotropic. Professor Schonbein has discovered that there are two kinds of ozone standing to one another in the relation of positively and negatively active oxygen ; namely ozone and antozone, which neutralize each other into common oxygen when brought into contact. In this x'espect they are analogous to electricity, and, like electricity too, one kind cannot be produced without a simultaneous development of the other.

When a metal, such as silver for example, is oxidized or rusts, it gives polarity to the atoms of oxygen in the atmosphere and divides them into the opposite states of ozone and antozone ; the ozone combines with the silver and msts or oxidizes it, at the same time that the antozone is dissolved in the moistui-e or aqueous vapour in the air and forms peroxide of hj'-drogen. The oxidized or rusted silver, as well as every other oxidized substance, is an ozonide, while the peroxide of hydi-ogen is an antozonide.

SECT. I.

OZONE AND ANTOZONE.

Since both kinds of ozone are' produced dm-ing tlie decomposition of water by electricity, and as sea air is always found to contain more or less free ozone, tbe ocean 'is probably an antozonide, for all tbe antozone formed by electricity during thunderstorms must be either dissolved in the sea-water, or carried into it in the form of peroxide of hydrogen by the rain. Ozone must be exceedingly abundant in the zone of calms and light breezes near the equator known as the variables, which is subject to heavy rains- and violent thunderstorms, and also in the regions of the monsoons. On land one of the benefits arising from these formidable phenomena is the production of ozone, which oxidizes decomposuag organic matter and hastens its decay, while the antozone, which is dissolved in the atmospheric vapour, forms the peroxide of hydrogen and frees the air from the antagonist principle.

The peroxide of hydrogen thus produced is a transj)arent colomiess inodorous liquid with a metallic taste, and contains one equivalent of hydrogen and two of oxygen. It retains its liquid state under a great degree of cold, and mixes with water in any proportion. It has a strong bleaching property, instantly destroying vegetable colour. If exposed suddenly to a temperature of boiling water it is decomposed with violent explosion, and readily gives off oxygen at 59° Fahr. The mere touch of an oxidilzed metal, as the oxide of silver, completely and instantaneously decomposes it, and oxygen gas is evolved by the union of the ozone and antozone so rapidly as to produce a kind of explosion attended by an intense evolution of heat.

During the combustion of phosphorus in the atmosphere both kinds of ozone appear, and Professor Schonbein considers the slow combustion of that substance, which unites with the ozone and sets the antozone free, as the type of all the slow oxidations which lo PHENOMENA OF C03IBUSTI0N. paet i.

organic and inorganic bodies undergo in moist atmospheric air; that true oxidation is always preceded by the appearance of the peroxide of hydi'ogen, and that this compound acts an important part in slow oxidations, and is deeply concerned in animal respiration, and in many other chemical actions going on in natiire.

In confirmation of these views, it is certain that ozone is a powerful minister in the work of decay. K wood be made explosive like gun-cotton by a similar process, it becomes pulverulent after a time, and burns without exploding, though it still retains its shape. In the natural state of the wood the oxygen is passive and quiescent, for oxygen is a constituent of wood ; in its second state it is explosive, and after a time that is succeeded by the semi- active state of ozone, which by a slow imperceptible combustion causes the wood to decay. Mr. Faraday observes that the force which would have been explosive had it been concentrated into one effort, expends itself in a long continued progressive change.

' The majestic phenomena of combustion bespeak our admiration and rivet our attention because of theii- imposing grandeur ; yet these are but spasmodic efPorts in the grand economy of the material world, occurrences of now and then. The slower but continuous progi-ess of the elements to their appointed resting-place, the silent, tranquil, ever progressing metamorphic changes involved in the phenomena of decomposition and decay, these we count for nothing and pass imheeded by. Yet with all their majesty, with all theii' brilliancy, all their development "of tremendous energy, what ai'e the phenomena of combustion in the grand scheme of the universe compared with these ? When the loud crash of the thunder or the lightning's flash awakens us from our thoughtless abstractions or our reveries, our feelings become impressed with the grandeur of Omnipotence and the might of the elements he wields, yet the whole fury of

SECT. I.

HYDROGEN.

the tliTinderstorni — what is that in comparison with the electric energies which silently and continually exert themselves in every chemical change ? Why, the electric force in a single drop of water, and disturbed when that water is decomposed, is of itself greater than in the electricity of a whole thunderstorm. Those of us who limit our appreciation of the powers of oxygen to the energies displayed by this element in its feebly active state, form but a very inadequate idea of the aggregate results accomplished by it in the economy of the world.' Oxygen is the only known gas that is allotropic, and is the only known substance that is doubly allotropic, that is existing in three different states similar to oxygen, ozone, and antozone.

Hydrogen when pure is an invisible gas withoiit smell or taste ; it is a constituent of various acids and alkalies, but is itself neither acid nor alkaline. It is highly inflammable, burning with a pale light, and, as already mentioned, a combined jet of oxygen and hydrogen produces heat of 8801°, which is so intense that nothing can withstand it. It is the lightest substance known. A balloon having the form of a globe ten feet in diameter, wovdd hold 32^ pormds weight of common air, while two pounds weight of hydrogen gas woiild fiU it. Associated with this small quantity of ponderable matter, hydrogen has an enormous power of combmation, but its activity is only called forth by some exterior and exciting cause. A mixture of two measures of hydrogen and one of oxygen gas would remain inert for ever, but the instant an electric spark is sent through it, a bright flash and an explosion takes place, and the result is water : thus a tremendous force lies quiescent in that bland element.

Hydrogen gas is introduced into the atmosphere by imperfect combustion, but it is instantly diffused and becomes harmless, for aeriform fluids are capable of rapid and perfect difi'usion through one another, each

NITROGEN.

PAKT I.

having a capacity peculiar to itself, wliicli under the same circumstances is greater as its density is less; therefore hydrogen the lightest of gases not only rises in the air on account of its levity, but is more quickly and completely diflFused than oxygen which is the support of life. Though hydrogen is inferior in densit}^ to every other gas, it surpasses them all in conductmg electricity, just as silver and copper conduct electricity better than platinum, though far less dense. The great refrigerating power of hydrogen is owing to its extreme mobility and consequent rapid convection of heat, in which it surpasses all other gases. It is as permeable to radiant heat as atmospheric air, has a very high refractive power, a specific heat of 3'2936, and may be substituted in many chemical formulse for a metal, without altering their character : hence it is sometimes called a metalloid.

The quantity of nitrogen gas or azote that exists in nature is enormous. It constitutes four-fifths of the atmosphere, whence it may be had in a pure state, as well as by chemical means. Like oxygen, this gas is permanently elastic, without smell, taste, or colour ; it is neither acid nor alkaline, it does not change vegetable colours, it neither burns nor supports combustion, and is incapable when breathed of supporting animal life. It abounds in organic bodies, in all parts of the animal texttire, in the blood, muscles, nerves, even in the brain; and is either a highly nutritious or poisonous principle in the vegetable kingdom.

Nitrogen gas is altogether passive ; it has no affinity for the metals, and cannot be liberated from any of its compounds even by electricity. Excepting boron and titanium, it will not combine directly or spontaneously with any simple element, even under the highest temperatm-e, but its indirect combinations are numerous and violent : those with hydrogen are either noxious or

A

SECT, I.

CARBON.

poisonous, those witli oxygen are all deadly poisonous. Had nitrogen combined spontaneously with either of these gases, especially with oxygen, life would have been impossible as the organized creation is constituted ; its inertness renders its mixture with oxygen in atmospheric air innocuous. However, combinations of nitrogen and hydrogen, forming nitrate of ammonia, have been discovered in the atmosphere by Professor Schonbein, the union of evaporation, heat and air being the cause ; and as evaporation is continually going on, he concludes that niti-ate of ammonia, nitrates and other salts are generated in the moist air, and are speedily washed down in otir rainy climates into the springs and rivers. He considers the formation of nitrates out of water as highly important for vegetation, because each plant becomes a generator of a portion at least of its azotized food, while the rain furnishes the ground on which it stands with a supply of the same.

In the atmosphere, nitrogen has all the mechanical properties of common air, but with a greater refractive power, and its specific gravity is nearly the same with that of oxygen. Since the atmospheric gases are the most permeable to radiant heat, the earth is in the most favourable circumstances for being warmed by the solar rays, and thus the properties of the elementary gases are admirably adapted for our comfort, nourishment, safety, and pleasure.