172 METALLOIDS. 



419. ANALYSIS OF THE AIR. The me- 



proportion of thod b Y which the relative amount of ox- 

 nitrogen deter- ygen and nitrogen in the air is determined 

 has been already given. On burning phos- 

 phorus under a glass jar, as there described, the water 

 is found to rise and fill a 

 little more than one-fifth of 

 the vessel, thereby indica- 

 ting that one-fifth of the 

 air which it contained was 

 oxygen gas. The remaining fths is nearly all nitro- 

 gen. In accurate experiments, a graduated tube is 

 employed, instead of a jar or tumbler. It is not es- 

 sential that the phosphorus should be ignited. With- 

 out ignition, it will gradually combine with all the 

 oxygen, and remove it from the air contained in the 

 tube. 



420. In order to determine the amount 



How is the . . 



amount of car- of aqueous vapor and carbonic acid in the 

 atmosphere, a gallon, or other measured 



nia deter- quantity of air, is drawn through tubes 



containing materials to absorb these sub- 



stances. This quantity is known by the increased 



weight of the tubes after the experiment is completed. 



421. THE APPARATUS DESCRIBED. The 



Describe the . f . 



apparatus apparatus used in the experiment is repre- 

 wfedinthis sen ted in the last figure. It consists of a 



analysis. 



bottle, or small cask, filled with water, and 

 provided with a cock below. The cock is turned, and 

 as the water no ws out, air flows in through the tube to 

 take its place. The quantity of air that has passed 



