NITROGEN. 171 



sodium chloride and ammonium nitrite, which latter substance is 

 a ternary compound of nitrogen, hydrogen, and oxygen; being 

 unstable, it is immediately decomposed by the heat, forming a 

 mixture of water vapour and nitrogen gas. The latter may be 

 collected over water at the pneumatic trough, like oxygen. 



Expt. 184. Another Method. Ordinary atmospheric air is 

 shown by Expt. 148 to be a mixture of oxygen and nitrogen, from 

 which the former can be removed by the action of pyrogallic acid 

 dissolved in caustic soda. Many other substances may be employed 

 in the same way ; for instance, phosphorus. 



Float on water a large bung, and on it put a bit of phosphorus 

 the size of a pea, carefully dried in blotting paper. Touch the 

 phosphorus with a hot wire, and it will begin to burn ; as soon as 

 this occurs hold over the bung and burning phosphorus a jar or 

 bell-shaped vessel (fig. 78), so that the bottom of the jar just 

 touches the water. At 

 first the heat of the burn- 

 ing phosphorus expands 

 the air, and drives a little 

 out, so that a few bubbles 

 escape under the edge of 

 the jar; the jar should 

 then be lowered so that 

 its mouth is an inch or 

 two under water. As the 

 phosphorus burns it ab- 

 sorbs the oxygen, and the 

 compound formed produces 

 a white cloud of solid F,g. 78. Preparat.onofNUrogen. 



oxide of phosphorus particles ; so that the bulk of gas in the jar 

 diminishes from the removal of the oxygen. Soon the flame 

 of the phosphorus goes out, all the oxygen being consumed ; let 

 the jar remain at rest for half an hour ; by that time the fumes 

 will have all subsided, and the gas in the jar will be clear ; it will 

 consist of nearly pure nitrogen. (Compare Expt. 169. Caution.) 



Expt. 185. To show that Nitrogen extinguishes Flame. 

 Prepare nitrogen in a bell jar with a stopper in the top ; when 

 the gas is clear remove the stopper, taking care that the jar is sunk 

 so deep in the basin that the water stands at the same level inside 

 and out. Introduce a lighted candle by a wire ; the candle will be 

 extinguished, just as in Expts. 71 and 149. 



Expt. 186. To reproduce Air from Nitrogen and Oxygen. 

 Prepare some nitrogen, and transfer it to a jar so as to fill it about 

 four-fifths full; this is done by depressing the jar containing the 



