34 COMBUSTION. 



Q. What is HYDROGEN.? 



A. An inflammable gas. The gas 

 used in our streets, is only the hydrogen 

 gas driven out of coals by heat. 



Q. What are the peculiar characteristics of 

 hydrogen gas ? 



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.* 



Q. What is OXYGEN ? 



A. A gas, much heavier than hydro- 

 gen ; which gives brilliancy to flame, and 

 is essential to animal life.f 



* 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. 



+ 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 



