A. Though this gas _itself_ will _burn_, yet a candle will _not_ burn when immersed in it; nor can an animal live in it. Hydrogen gas is the lightest of all known substances.[7] [7] Hydrogen gas may be made thus:--Put some pieces of zinc or iron filings into a glass: pour over them a little sulphuric acid (vitriol), diluted with twice the quantity of water; then cover the glass over for a few minutes, and hydrogen gas will be given off. EXP. If a flame be put into the glass, an EXPLOSION will be made. If the experiment be tried in a phial, which has a piece of tobacco-pipe run through the cork; and a light held a few moments to the top of the pipe, a FLAME will be made. If a balloon be held over the phial, (so that the gas can inflate it,) the balloon will ascend in a very few minutes. Q. _What is OXYGEN?_ A. A gas, much heavier than hydrogen; which gives brilliancy to flame, and is essential to animal life.[8] [8] Oxygen gas is much more troublesome to make than hydrogen. The _cheapest_ plan is to put a few ounces of manganese (called the black oxide of manganese) into an iron bottle, furnished with a bent tube; set the bottle on a fire till it becomes red hot, and put the end of the tube into a pan of water. In a few minutes, bubbles will rise through the water; these bubbles are oxygen gas. These bubbles may be collected thus:--Fill a common bottle with water; hold it topsy-turvy over the bubbles which rise through the pan, but be sure the mouth of the bottle be held _in the water_. As the bubbles rise into the bottle, the water will run out; and when all the water has run out, the bottle is full of gas. Cork the bottle while the _mouth remains under water_; set the bottle on its base; cover the cork with lard or wax, and the gas will keep till it be wanted. N. B. The _quickest_ way of making oxygen gas, is to rub together in a mortar half an ounce of oxide of copper, and half an ounce of chlorate of potassa. Put the mixture into a common oil flask, furnished with a cork which has a bent tube thrust through it. Heat the bottom of the flask over a candle or lamp; and when the mixture is red hot, oxygen gas will be given off. Note--the tube must be immersed in a pan of water, and the gas collected as before. (Chlorate of potassa may be bought at any chemist's; and oxide of copper may be procured by heating a sheet of copper red hot, and when cool, striking it with a hammer: the scales that peel off, are oxide of copper.) EXP. Put a piece of red hot charcoal, (fixed to a bit of wire,) into your bottle of oxygen gas; and it will throw out most dazzling sparks of light. Blow a candle out; and while the wick is still red, hold the candle (by a piece of wire,) in the bottle of oxygen gas; the wick will instantly ignite, and burn brilliantly. (Burning sulphur emits a _blue_ flame, when immersed in oxygen gas.) Q. _What is NITROGEN?_