150 FARADAY 



and oxygen, we had pure oxygen as our atmosphere; what 

 would become of us? You know very well that a piece of 

 iron lit in a jar of oxygen goes on burning to the end. 

 When you see a fire in an iron grate, imagine where the 

 grate would go to if the whole of the atmosphere were 

 oxygen. The grate would burn up more powerfully than 

 the coals ; for the iron of the grate itself is even more com- 

 bustible than the coals which we burn in it. A fire put into 

 the middle of a locomotive would be a fire in a magazine 

 of fuel, if the atmosphere were oxygen. The nitrogen 

 lowers it down and makes it moderate and useful for us, 

 and then, with all that, it takes away with it the fumes that 

 you have seen produced from the candle, disperses them 

 throughout the whole of the atmosphere, and carries them 

 away to places where they are wanted to perform a great 

 and glorious purpose of good to man, for the sustenance of 

 vegetation, and thus does a most wonderful work, although 

 you say, on examining it, " Why, it is a perfectly indifferent 

 thing." This nitrogen in its ordinary state is an inactive 

 element; no action short of the most intense electric force, 

 and then in the most infinitely small degree, can cause the 

 nitrogen to combine directly with the other element of the 

 atmosphere, or with other things round about it; it is a 

 perfectly indifferent, and therefore to say, a safe substance. 

 But, before I take you to that result, I must tell you 

 about the atmosphere itself. I have written on this diagram 

 the composition of one hundred parts of atmospheric air: 



Bulk. Weight. 



Oxygen 20 23.3 



Nitrogen 80 77.7 



100 i oo.o 



It is a true analysis of the atmosphere so far as regards the 

 quantity of oxygen and the quantity of nitrogen present. 

 By our analysis, we find that 5 pints of the atmosphere con- 

 tain only i pint of oxygen, and 4 pints, or 4 parts, of nitro- 

 gen by bulk. That is our analysis of the atmosphere. It 

 requires all that quantity of nitrogen to reduce the oxygen 

 down, so as to be able to supply the candle properly with 

 fuel, so as to supply us with an atmosphere which our lungs 



