2 AGRICULTURAL CHEMISTRY 



verizing of limestone, and similar changes which do not 

 affect the composition of the material, are physical 

 changes. When milk sours, fruits decay, or wood is 

 burned, a different kind of change takes place. The 

 smallest particles of which each of the materials is com- 

 posed undergo a change in composition. The products 

 formed are entirely different in character from the origi- 

 nal substances. Such changes, which affect the identity 

 or individuality of a material, are chemical changes. 



2. Physics is the science which concerns itself with the 

 changes which matter undergoes when the ultimate par- 

 ticles of a material retain their identity or individuality. 



Animal and plant life are to a great extent dependent 

 upon the physical changes which take place in the soil. 

 Rain is the result of the action of physical agencies, as is 

 also the pulverization of rocks and soils. In all manu- 

 facturing operations, and as the result of all kinds of 

 manual labor, particularly upon the farm and in the 

 workshop, physical changes are continually taking place. 



3. Chemistry is the science which deals with the 

 changes which matter undergoes when the ultimate par- 

 ticles lose their identity or individuality, and the prod- 

 ucts formed are entirely different from the original mate- 

 rial. 



Chemical changes are continually taking place. 

 Plant growth and animal life are dependent largely upon 

 the chemical as well as the physical changes which take 

 place in the soil and in the air. Life processes are inti- 

 mately associated with chemical changes. Chemical and 

 physical changes are closely related ; a chemical change 



