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The method of making experiments on the gases is described under the head of " Chemical Utensils, article, gas apparatus."
88. We have no knowledge of the properties of oxygen, except in a state of combination. It sometimes exists in a solid state, as when it combines with the metals to form oxides, and sometimes in an aeriform state, as when it is united to caloric and light, forming oxygen gas. No process has yet separated the oxygen from the solid, and the aeriform state at the same time ; the consequence is, that the base, or ponderable part of oxygen gas has never been examined in a separate state.
89- Oxygen is an invisible fluid like air. It has neither taste nor smell. Its-specific gravity 1103, air being 1000. It is slightly absorbable by water. It is procured from a great number of substances ; and forms about one fifth of the atmosphere.
OXYGEN GAS.
Exp. Take a "quantity of black oxide of manganese, puf it into a retort, or Florence flask, furnished with a tube, (ree chemical utensils) and pour on one half its weight of sulphuric acid: mix them together* and place the retort, or flask over an Argand lamp. The, gas comes over in abundance, and may be collected over water in the usual way, by plunging the beak of the retort, under a vessel filled with it. See gas apparatus.
Caution.—When bubbles of oxygen cease to ascend up the water in the receiver, the retort must be removed, otherwise it will be broken by the water which will be forced over to fill the vacuum caused by the heat.
Obs. The above, is the most convenient method of collecting oxygen gas in the small way, and for ordinary experiments ; where larger quantities are wanted, other methods are used.
90. Oxygen gas may also be obtained from black oxide of manganese, heated to redness in an iron retort, or gun barrel:
91. From red lead heated in the same way.
92. From nitrate of potash, (common salt petre) also heated as above.
93. From the leaves of plants, exposed to the action of the sun, under a receiver filled with water, &c.
94. All combustibles burn in this gas with greatly increased splendour.
Exp. 1. Fill a glass vessel, as an open-mouthed vial with this gas; then as it stands on the shelf of the water-bath, slide a plate of glass under its mouth and set it upright, keeping the glass in its place. Have ready a wax-taper fixed to a piece of wire; light the taper, and sliding the plate of glass hastily off, plunge it into the gas. The taper will burn with intense brilliancy. .
95. If the taper be blown out, and instantly be plunged into the gas, it will be lighted again, with a slight explosion.
Obs. As tapers, ready made, cannot always be obtained, it was thought worth while to add here, that a strip of cotton cloth, or some cotton wick, dipped in melted bees-wax, and rolled moderately hard while the wax is cooling, will answer every purpose.
Several of the metals when heated in a vessel of oxygen gas, inflame, and burn with great brilliancy.
2. Take some thin pieces of zinc, such as are made by melting that metal, and pouring it into water; place a small quantity of them on a spoon, or small dish, made by hammering a piece of tinned iron concave, and fixing to it a wire handle. Place in the midst of the zinc a grain, or two, of phosphorus ; then set fire to the phosphorus, by holding the dish over a candle, and instantly plunge it into a vessel of oxygen gas. The zinc will be inflamed and will burn with a beautiful white light.
￡k Procure some iron, or what is better, steel-wire, or a watch-spring; wind it round a slender rod of glass, or wood, so as to coil it up in a spiral form : the turns of the wire being about the eighth of an inch apart. Then withdraw the rod, and tie to the end of the wire a piece of thread, dipped in melted sulphur, or becs-wax; leave the other end of the wire strait for a few inches, which must be fixed to a cork, in such a manner that the coil will hang vertically when the cork is in its place. Fill a bottle holding about a quart with oxygen gas, and set its mouth upwards, covering it with a plate of glass. Then light the sulphur, or wax. and introducing the coil into the bottle, put the cork in its place. Fig. 21. The iron will burn with an inconceivably brilliant light, throwing out sparks in all directions. Now and then a globule of the melted iron - falls down and will break the bottle unless some sand or water be left at the bottom. See fig'.

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