General Principles. 49 



the vapour, and is sensible to the smell, and the 

 scales which fall off are oxide of iron. But the 

 usual method of obtaining hydrogen gas is by 

 pouring sulphuric acid diluted with water upon 

 zinc or iron filings. In this case the metal is 

 converted into an oxide, or rather a salt (sulphat 

 of iron or zinc), which contains a superabun- 

 dance of oxygen. Thus the watery fluid is 

 decomposed, the oxygen entering into the com- 

 position of the salt, while the hydrogen flies off 

 in the form of hydrogen gas. The same appa- 

 ratus will answer for this experiment as that 

 described above for the obtaining of oxygen gas. 



If a phial is filled with this gas, and a candle 

 is brought to its mouth, it will burn, as it rises 

 by its levity out of the phial, till the whole is 

 consumed. It is incapable, however, of sup- 

 porting flame or combustion of itself; for if a 

 lighted taper is plunged into a jar of hydrogen 

 gas, it will immediately be extinguished. These 

 phaenomena admit of an easy explanation on the 

 principles already established. Hydrogen gas 

 burns like other combustibles by its strong at- 

 traction for oxygen, with which it forms water 

 and both gasses being condensed, the caloric 

 which kept them in the gaseous state is set free, 

 and becomes sensible in the form of flame. The 

 air of our atmosphere, you have seen, contains 

 about twenty-three parts in a hundred of oxygen 

 gas> and while there is a fresh supply of it the 

 hydrogen gas will continue to burn. Hydrogen 



VOL. ii. D 



