Scientific Lectures. 251 



To understand the eliartacter of this composite atmosphere, some 

 expLinations and experimental ilhistrations of the properties of the 

 prominent constituents are necessary. In pursuance of this phm 

 your attention is called to the jar placed upon the table. It has 

 been filled with nitrogen gas ; as you perceive, it is colorless, and if 

 you were to test it as regards its taste and smell, you would find it 

 devoid of both. It, however, possesses properties of interest in its 

 relation to combustion and respiration. To illustrate the first of 

 these, I introduce a few candle flames into the atmosphere of nitro- 

 gen. As you see, they are instantly extinguished, not even a spark 

 remaining to bear witness to the action that a few seconds ago was 

 so vivid and beautiful. If, instead of the candle flame, we place a 

 living, warm blooded creature in nitrogen gas, the vital flame that 

 animates it, giving the powers of motion, sensation and will, is also 

 extinguished, and like the candle flame, it has gone, no man knows 

 wliither. 



From nitrogen let us turn to the second of the invariable con- 

 stituents. Here we meet with an altogether diftcrent substance, and 

 though, as we look at the oxygen in yonder jar, it is not visibly 

 distinguishable from the nitrogen we have just examined, but is 

 equally colorless, odorless and tasteless, we find that it acts in a very 

 different manner wlien the candle flames are submitted to its influ- 

 ence. See how brilliant they become as they dip into and drink up 

 the vital air, as it has been so aptly named. See how rapidly the 

 combustible wax wastes away. Even the candles that only bore 

 sparks, are now crowned with brilliant flames. Could any action 

 contrast more thoroughly Avith that we witnessed a few moments 

 ago ? That annihilated the flames, this vitalizes them. 



Though the experiment you have seen gives an idea of the differ- 

 ence in the chemical action of these two gases, it does not afford as 

 just an estimate of the power of oxygen as may be obtained from tlie 

 illustrations to which your attention is now called. Sulphur (as all 

 who have ignited a lucifer match know) burns with a feeble, pale 

 blue flame, but see how it acts in the atmosphere , of oxygen. How 

 great the increase in the rapidity of combustion ! How beautiful the 

 light ! Watch the heated products of combustion as they rise to the 

 top of the jar to seek an outlet, and so afi'ord an illustration of the 

 means to which we must resort if we desire to remove the foul gases 

 from an apartment, and ventilate it successfully. 



The last illustration of the properties of oxygen that we shall 



