HYDROGEN. 205 



position. It may be turned upward into a vessel full of air, and will 

 expel it, and take its place. 



(A.) Suspend, out of the water of the pneumatic cistern, a tall nar- 

 row jar, full of the gas, keeping a glass plate over its mouth, until it 

 is fixed in its place : then withdraw the plate without agitation ; on 

 putting a burning candle to the mouth, a quarter of an hour after, 

 the gas will take fire with the usual slight explosion, and will then 

 continue to burn quietly away, thus proving that owing to its levity, 

 the pressure of the atmosphere had kept it in its place. 



(i.) Reverse the experiment, by filling the same jar again with 

 the same gas ; cover its mouth with the glass plate, and turn it up ; 

 let an assistant hold a candle a foot above, and when the plate is 

 withdrawn, the gas, now rapidly rising, will take fire as it is passing 

 upward, and will exhibit a volume of flame in the air : the same 

 pressure which in the former experiment kept it in its place now 

 forces it to rise. 



6. EFFECTS ON ANIMAL LIFE. 



It is hostile to life, but not instantly fatal. 



(a.) The lungs may be inflated with it a few times in succession, 

 and it may be blown out without injury.* It produced in Mr. Mau- 

 noir and Mr. Paul, at Geneva, a soft, shrill, and squeaking voice, 

 when they attempted to speak, after breathing it. 



(b.) Frogs placed in hydrogen gas will suspend their respiration; 

 they have been known to do it for 3J hours at a time. 



(c.) In mixture with oxygen, it may be substituted for the nitro- 

 gen, and a respirable atmosphere might thus have been made ; but, 

 the mixture would have been explosive, and the hydrogen would 

 probably have separated from the oxygen in consequence of its levity. 



(d.) It kills by suffocation, merely or principally, as water does. 



(e.) It is not noxious to plants, and some, it is said, even absorb it. 



7. NATURE OF HYDROGEN. 



It is an element in relation to our knowledge, and probably it is a 

 real element. It is a simple combustible. 



8. ITS IMPORTANCE AND DIFFUSION. 



(a.) It is probably, next to oxygen, the most important element ; 

 it is exceedingly abundant, and its compounds meet us almost every 

 where. 



(b.) It exists in water, and all fluids used by men and animals for 

 drink or diluents. 



* Pilatre de Rozier was accustomed, not only to fill his lungs with hydrogen gas, 

 but to set fire to it as it issued from his mouth, where it formed a very curious jet 

 of flame. He also mixed pure hydrogen gas with one ninth of common air, and re- 

 spired the mixture as usual ; " but when he attempted to set it on fire, the conse- 

 quence was an explosion so dreadful, that he imagined his teeth were all blown 

 out." 



