*

mixture of two parts by measure of hydrogen with one part of oxygen will explode most violently if ignited, and a small jet of it in a state of ignition produces a most powerful heat, causing steel and platinum to melt instantly like wax. A jet of this gas ignited on lime produces that intense light called Drummond's Signal Light, and is that by which objects seen in the oxy-hydrogen microscope are illuminated.

Hydrogen gas is frequently found combined with carbon in mines and coal-pits, and is by the miners called firedamp. It sometimes generates very suddenly, when, on the introduction of a light, an explosion takes place, producing the most fatal effects. Sir Humphry Davy, in order to prevent the dreadful results above alluded to, invented some years since a lamp called a safety-lamp, which miners may use without risk. The safety-lamp is a lamp surrounded with fine wire gauze, and is so formed through the fact that flame will not pass through small apertures in metallic substances. A stream of hydrogen gas from a small orifice made to fall upon a piece of spongy platinum will render the platinum red hot, and ignite the gas.

Hydrogen gas is easily obtained for experiment by pouring a mixture of one part of sulphuric acid with four or five parts of water, over iron filings, or what is much better, over granulated zinc in a retort; by the action of the acid the water becomes decomposed, the oxygen unites with the metal and forms an oxide, while the hydrogen escapes. This gas, in combination with carbon, similar to the fire-damp above named, may be obtained in great abundance in the summer time from ditches or other stagnant water, by inverting a vessel filled with water, and stirring up the bottom of the ditch with a stick, when large bubbles will rise, which may be caught in the vessel.

Hydrogen is abundantly distributed in nature, forming one of the ingredients of all oils, fat, bitumen, &c., while carbon forms the other. Hydrogen gas unites with several other substances, forming compounds, as carburetted hy

* A jet of oxygen gas made to pass through the flame of a spirit lamp will produce nearly the same effect; alcohol being almost pure hydrogen.

drogen,* sulphuretted hydrogen,+ phosphuretted hydrogen, and others, being severally carbon, sulphur, and phosphorus in union with hydrogen gas.

There are one or two other gases, which it is intended to notice on account of their peculiar nature and striking qualities.

The first of these is Chlorine, which takes its name from its colour-a greenish yellow. It possesses the peculiar property of supporting combustion, while it will not support life. If attempted to be respired, it produces a sense of strangulation, with a violent coughing and spitting of blood, yet in contagious diseases, as the typhus fever, cholera, &c., fumigations of this gas§ will destroy the contagion, and very generally preserve health. Water will readily combine with chlorine, and acquires the property of discharging the colours of printed linens and muslins. If any of the metals in powder or leaves, as antimony, Dutch metal, gold-leaf, &c., be thrown into a vessel filled with this gas, they will instantly ignite.

Chlorine is made for experiment as follows:-Mix three parts of common salt with one part of black oxide of manganese, and having introduced the mixture into a glass retort, pour upon it two parts of sulphuric acid, and apply the heat of a lamp, the gas will come off abundantly, and must be collected by means of the pneumatic trough.

* Common coal gas is carburetted hydrogen gas, and its brilliancy is produced by the carbon. It may be made in a pure way by mixing one part of alcohol or spirits of wine with four parts of sulphuric acid, and subjecting the mixture to the heat of a lamp in a glass retort. This is also called Olefiant gas.

+ It is this gas which escapes from drains, and is of a very poisonous nature, even when much diluted with atmospheric air. A dog would die speedily in an atmosphere containing one part in 800 of this gas, and a horse in an atmosphere containing one part in 250.

This gas is the most combustible body known; it ignites spontaneously in atmospheric air. It may be made by putting some small bits of phosphorus into a small glass retort, and pouring over it some liquor potassa. The heat of a lamp should be applied, and the beak of the retort be immersed in a vessel of very warm water. It will soon generate, and each bubble will ignite with a sudden flash at the instant of its extrication.

Chloride of lime is now generally used for this purpose; a tablespoonful is dissolved in a glass of water, and sprinkled about the room.

Great care should be taken that it does not escape in a room, as a comparatively small quantity will produce a violent irritation of the lungs. It combines with certain salts and metals, and its combinations are termed chlorates and chlorides.

Nitrous oxide gas is the last intended to be noticed, and is a compound of oxygen and nitrogen. It supports combustion better than common air, and may be respired. But the effects produced by inhaling it constitute its chief peculiarity. The most pleasurable sensations are the general results, producing immoderate fits of laughter, whence it has obtained the name of laughing gas. The excitement in some persons is so great as to produce violent muscular motion, and an inclination to leap and run. Unlike excitements in general, it does not appear to leave any unpleasant feeling after the excitement has subsided. This gas is obtained from crystals of nitrate of ammonia, by submitting them to the heat of a lamp in a glass retort.

GEOLOGY.

Geology defined-Arrangements of the various strata of the Earth-Divisions of Strata-Primitive Class-Subdivided into the orders Silicious, Aluminous, Calcareous, and Ponderous-Metals in Primitive class-Tin, Silver, Quicksilver, Platinum, Gold-Secondary Class-Subdivided into Silicious, Aluminous, and Ponderous-Metals in Secondary class-Copper, Antimony, Zinc, and Lead-Transitive Class-Subdivided into Aluminous, Calcareous, and Ponderous-Metals in Transitive class-Iron, Cobalt, and Manganese -Flat or Flatz Class-Subdivided into Aluminous, Calcareous, and Ponderous-Coal formations-Alluvial Class-Subdivided into Aluminous, Calcareous, Inflammable, and Light formations-Volcanic Class-Volcanic action considered-Volcanic eruptions-Result of Geological investigation -Extinct race of animals described-The Mammoth-The Mastadon-The Megatherium-The Dinotherium, &c. &c.

GEOLOGY is the art of distinguishing the component parts of the globe of the earth, and the science of accounting for the phenomena which present themselves in the investigation.

The materials of which the earth is composed are arranged in a very beautiful order, one above another; with only the little confusion which has arisen from Floods, Earthquakes, and Volcanic Eruptions. Providence has, however, watched over this very confusion, so as to make

it a blessing to mankind. Thus have we a double proof of the existence and benevolence of the Great Creator.

If the strata of the earth had been arranged simply according to specific gravity, many of them would have been buried at such a depth, as to be entirely beyond the reach of man. These strata present themselves, however, at an inclination, so that the extremity of each offers itself in turn at the very surface of the earth, and tells mankind exactly how far below it or from it any other stratum is placed.

The various strata of the earth may be divided into Six Classes. The first and second are inorganic; the third and fourth are organic; and the fifth and sixth, including volcanic productions, may be described as amorphous.

I. PRIMITIVE CLASS.

The PRIMITIVE CLASS of Minerals are such as are supposed to lie at the centre of the earth, or nearest to the centre. They are called primitive, because they are either simple substances of one material, as Quartz, or they are composed of simple substances, so mixed that it is impossible to tell which of the component parts was first in existence, as Granite, which is composed of Quartz, Feldspar, and a third substance, generally Mica.

This class may conveniently be subdivided into the Orders Silicious, Aluminous, Calcareous, and Ponderous.

Silicious minerals will strike fire with steel; they will taste gritty between the teeth ;-when rubbed together in the dark, they will yield a kind of phosphorescent light; and if ground very fine, and mixed with potash, may be made into glass, which may be done by a blowpipe on a piece of

charcoal.

Opaque Quartz, commonly whitish, is used for paving the streets; when black, it is called flint, and is used in pottery manufactories;-when varied in its appearance, it is called Chertz, and is used in mills for grinding;when blood-red or brownish, it is called Jasper, and is used for burnishing gold.

Translucent Quartz, when flesh-white or flesh-red, is called Carnelian; when nail-white, it is called Onyx stone

or Sardonyx stone or Chalcedon; when gold-coloured, it is called Topaz; when dark red, it is called Garnet; and when the crystals are of a smoky appearance, it is called Cairne Gorne.

Transparent Quartz is called Scotch Pebble. If it have parallel lines of Jasper, it is called Agate; if it have appearances of arborescence, it is called Mocha stone; and if it be beautifully crystallized, it is used as a substitute for diamond. If any doubt should exist respecting such a mineral, put it between two large penny-pieces, so that the edges may touch on one side; press the pennypieces between the thumb and finger, if the mineral be reduced to powder it is not diamond; then rub the pennypieces together while the fragments are between them, if the surface be scratched, the mineral is Silicious.

The varieties of this order are Porphyry, which is of a brownish colour; and the different coloured Granites, which are composed of Quartz, which is glassy and rough in its fracture; Feldspar, which is tabular and smooth in its fracture; and generally Mica, which can be cut with a knife.

Aluminous minerals are adhesive to the tongue, and when breathed on give out an unpleasant smell, so much so that one specimen of this order is called Stink stone. To this order belong Compact Feldspar, which is used for Glazes, and called Cornish stone; Egyptian Feldspar, which is red; and Labrador Feldspar, which is green, and when polished is very beautiful; Pipe-clay not coloured, and Lydian stone coloured, both of which remove grease spots; Mica, which is elastic; Talc, which is non-elastic; and Hornblende, which is a mineral of the same nature, but of a dark colour.

Calcareous minerals are chiefly of three sorts :-Carbonate of Lime, which will effervesce with cold Sulphuric Acid or Vitriol, and is called Statuary Marble; Italian Marble; Dogtooth Spar; Dolomite; and Icelandic Spar.* Sulphate of Lime, which will not effervesce with vitriol, and is called Gypsum, Alabaster, and Plaster of Paris;

* If a piece of Icelandic Spar be placed over an ink line, the line will appear double; and in whatever way this mineral is broken, the fragments are always rhomboidal.