Illustrations of Chemistry.
(Continued from No.5.)

THE GASES.—There are several kinds of substances, which are not known to exist uncombined, except in a gaseous state. Of these the most common are oxygen, hydrogen and nitrogen. There are also several kinds of gases, composed of one or more of the above, united with other bodies; of these are the carobonic acid gas, muriatic acid gas, and the nitrous oxyde, or exhilarating gas, with many others. Oxygen readily combines with some of the metals, forming what is termed oxydes. The common rust of iron, is an oxyde of that metal. All the pigments and mineral colours used by painters, are oxydes of different kinds of metals, though sometimes combined with other materials. All oxydes are much heavier than the metals on which they are based. Oxygen supports combustion, and readily unites with combustibles, forming ashes or compound gases. Combined with hydrogen, in the proportion of 85 to 15, it forms water; and combined or rather mixed with nitrogen and carbon, in the proportion of 22 parts oxygen, 77 of nitrogen, and 1 of carbon, it forms atmospheric air. Pure oxygen gas may be readily procured by decomposing any of the substances which contain its base. It is an essential constituent, and is supposed to constitute the acidifying principle of all acids; and its presence is essential to vegetable and animal life.

EXPERIMENTS.—Heat a piece of common lead to a red heat, and expose it while hot to a current of atmospheric air;—The oxygen of the air will combine with the lead, and it will become red lead; and will be found to be much heavier than the original.

Place a little red lead on a piece of charcoal, and force the flame of a lamp upon it, by a flow pipe, and the oxygen will combine with the charcoal, forming carbonic acid gas, and the lead will be restored to its metallic state.

Place a little red lead in a phial, and add a few drops of suphuric acid, and apply a flame of a lamp to the bottom of the phial, and oxygen gas will be liberated, and rise through the neck of the phial.

Burn a little sulphur (brimstone) in open air, and hold a piece of wet cloth over the vapor which rises from it;—the moisture of the cloth will immediately become sharply acidulated to the taste, being a real sulphurous acid.

Place a lighted candle or taper in a bottle containing oxygen gas, and the combustion and flame will become exceedingly brilliant. Place a fire fly in a phial of oxygen gas, and it will appear exceedingly animated and lively, and its illumination will be much more brilliant, than when in common air.

(To be continued.)