122 



AGRICULTURAL CHEMISTRY 



sented graphically by the use of blocks in Fig. 53. A 

 represents the arrangement before, and B the arrange- 

 ment after the reac- 

 tion. Observe that in 

 this equation there is 

 the same number of 

 atoms of each element 

 on each side of the 

 equation. After writ- 

 ing an equation the 

 student should always 

 observe whether or 

 not it is properly bal- 

 anced, and that rea- 

 sonable products are 

 formed. The valences of the elements and radicals are 

 given in Sections 15 and 77. 



There are always as many parts by weight of the ele- 

 ments on one side of an equation as on the other. That 

 is, the sum of the weights of the atoms and molecules on 

 one side is equal to the sum of those on the other, as : 



B 



53- Graphic illustration of a chemical 

 reaction. 



117 



98 



117 -f 98 = 215. 



73 



142 

 73 + 142 = 215. 



In the case of trivalent and bivalent elements and radi- 

 cals, as in the reaction between H 3 PO 4 and Ca(OH),, it 



