48 Chemistry. [Lecture 25. 



from the experiments of Sir H. Davy, to con- 

 tain about fifty-seven parts in the hundred of 

 oxygen, to forty-three of nitrogen. 



IV. HYDROGEN, as its name imports, is the 

 basis or constituent of water, being derived from 

 the Greek hi/dor, water. Because it is the con- 

 stituent of water, however, it does not follow 

 that this ingredient constitutes the largest pro- 

 portion : for, in fact, water contains eighty-five 

 parts of oxygen to fifteen of hydrogen. 



Like oxygen, hydrogen is never found but in 

 a state of combination ; the nearest approach to 

 a state of purity is that in which it is combined 

 only with caloric, or in the form of hydrogen gas. 



This gas was formerly known by the name of 

 inflammable air, from its property of easily 

 catching fire. From its great degree of levity, 

 being twelve times lighter than common air, it 

 has been employed for the inflating of air 

 balloons. 



Being a constituent part of water, whatever 

 process decomposes water will produce hydrogen 

 gas, provided the oxygen is absorbed by any 

 matter, or otherwise disposed of. Thus, if water 

 is dropped gradually through a gun-barrel made 

 red hot in the middle, the water will be decom- 

 posed ; the oxygen will form an oxide or rust 

 with the iron, and the hydrogen will come out 

 pure by a tube at the other end. The same 

 effect is produced as often as a smith plunges a 

 red hot iron in water. The hydrogen rises with 



