NITROGEN. 85 



Properties. Nitrogen is a colorless, inodorous, tasteless gas; 

 which, at a temperature of 130 C. (202 F.) and a pressure of 

 280 atmospheres, may be condensed to a colorless liquid. It is neither, 

 like oxygen, a supporter of combustion, nor, like hydrogen, a com- 

 bustible substance ; in fact, nitrogen is distinguished by having very 

 little affinity Jor_anypther element, and it scarcely enters directly into 

 combination with any subsFa~nce. Nitrogen is not poisonous, yet not 

 being a supporter of combustion it cannot sustain animal life. 

 Nitrogen is trivalent in some compounds, quinquivalent in others. .>> f\ 



Atmospheric air is a mixture of about four-fifths of nitrogen and 

 one-fifth of oxygen, with small quantities of aqueous vapor, carbon 

 dioxide, and ammonia, containing frequently also traces of nitrous or 

 nitric acid and occasionally hydrogen sulphide, sulphur dioxide, and 

 hydro-carbons. Besides these gases there are always suspended in the 

 air solid particles of dust and very minute cells of either animal or 

 vegetable origin. 



100 volumes of atmospheric air contain of 



Oxygen 20.61 volumes. 



Nitrogen 77.95 " 



Carbon dioxide ..... 0.04 " 

 Aqueous vapor .... 5-1.40 " 

 Ammonia \ 

 Nitric acid t 



An analysis of air may be made by the following method : A graduated glass 

 tube, containing a measured volume of air, is placed with the open end down- 

 ward into a dish containing mercury. A small piece of phosphorus is then 

 introduced and allowed to remain in contact with the air for several hours, 

 when it gradually combines with the oxygen. The remaining volume of air is 

 chiefly nitrogen, the loss in volume represents oxygen. 



For the determination of carbon dioxide and water, a measured volume of 

 air is passed through two U-shaped glass tubes. One of these tubes has previ- 

 ously been filled with pieces of calcium, chloride, the other tube with pieces of 

 potassium hydroxide, and both tubes have been weighed separately. In pass- 

 ing the measured air through these tubes the first one will retain all the 

 moisture, the second one all the carbon dioxide ; the increase in weight of the 

 tubes at the end of the operation will give the amounts of the two constituents. 



That oxygen is found in the atmosphere in a free state is explained 

 by the fact that all elements having affinity for oxygen have entered 

 into combination with it, whilst the excess is left uncombined. Nitro- 

 gen is found uncombined, because it has so little affinity for other 

 elements. 



