138 THE AIR 



the air. Some of those which are beneficial in the soil as 

 agents for the decomposition of organic matter, nitrification, 

 and nitrogen fixation are carried in this way. Disease germs 

 are also present. Particles of dust are of value in serving 

 as nuclei for the precipitation of water vapor, and thus 

 forming clouds. In some places the presence of sulphur 

 dioxide is harmful. 



REFERENCES 



Erdmann. Lehrbuch der Anorganischen Chemie. 



Newth. Inorganic Chemistry. 



Smith. General Chemistry for Colleges. 



Any other good text-book on general chemistry. 



