MIXTURES 211 



carefully holding the jar. As the P burns (combining with O), 

 the oxygen that was in the jar is used up, leaving the nitrogen 

 nearly pure. The O combines with the P, the compound then 

 being dissolved in the water. Thus the air in the jar loses from 

 its total volume the volume of the O that was in it at first, and 

 the water rises into the jar to take its place. Compare the volume 

 of water that so rises with that of the gas still left in the jar. 

 Of what is this gas largely composed now ? 



Experiment 133. Carefully cover the jar under water ; then 

 lift it out and set it right side up on the table. Carefully uncover, 

 at once thrusting a lighted splinter into the jar which is now 

 filled with N. Does N support combustion ? 



The use of O in the atmosphere is to help support 

 animal life, and to support combustion. Nitrogen, being 

 very inactive, serves to check too strong an action of O ; 

 in an atmosphere of pure O fires would burn beyond 

 control and animals could not live. The use of CO 2 in 

 the air is to supply to plants the C that they need in 

 making starch and cellulose. Water vapor in the air 

 serves to temper the climate of some places, and is very 

 important in furnishing rain. Without evaporation and 

 rainfall the soil would everywhere become dry and the 

 water would slowly drain from the land into the ocean. 



247. Soil. The earth is thought to be composed of 

 solid rock. A great deal of its surface is covered with 

 a layer of loose earthy matter called soil, which varies 

 in thickness from an inch or two to several hundred 

 feet in some places. On the average the soil is but a 

 few feet deep. Soil is made of tiny particles of rock 

 that have been worn off from the solid rock mass in 

 different ways. As the kinds of rock that have been 

 thus worn are many, so we find many different kinds of 



