THE CHEMISTEY OF WATEE. IIYDEOGEX. 



121 



152. Breathing Hydrogen. This gas can not be breathed 

 alone for any time, simply because life can not be con- 

 tinued without oxygen. But oxygen and hydrogen can 

 be breathed together with impunity, showing that hy- 

 drogen does not act as a poison when introduced into 

 the lungs. It is in this respect like nitrogen, and un- 

 like carbonic anhydride. Of course it can be breathed 

 with air, though not in so large proportion as with pure 

 oxygen. 



153. Sounds in Hydrogen. If a bell be rung in a jar 

 of hydrogen gas the sound can be 



scarcely heard, because the gas is so 

 very rare a medium. It is for the 

 same reason that sounds are so faint 

 in the attenuated air on the tops of 

 very high mountains. So, also, if one 

 speaks immediately after breathing in 

 a mixture of hydrogen with oxygen 

 or air, his voice has a small, squeaking 

 sound. If the common speaking toy 

 be made to utter its voice in a jar 

 of hydrogen, as represented in Fig. 45, 

 the sound is very laughable. 



154. Illuminating Gas. In the common gas that we burn 

 we have a mixture of hydrocarbons, or compounds of hy- 

 drogen with carbon. There are two forms of this combi- 

 nation, or rather two distinct compounds. They are marsh 

 gas and olefiant gas, sometimes called the light and the 

 heavy carburetted hydrogen. There is exactly twice as 

 much carbon in the latter as in the former one being CH 4 , 

 and the latter C 2 H 4 . The light carburetted hydrogen is the 

 fire-damp of coal-mines, which by its explosions destroyed 

 so many lives before Sir Humphrey Davy invented his 

 safety-lamp (Part I). It is also one of the products when 



F 



Fig. 45. 



