12 AGRICULTURAL CHEMISTRY 



Approximate Va- Kind of 



Name. Symbol, atomic weight, lence. element. 



Nickel Ni 59 2,4 Base-forming 



Nitrogen N 14 3,5 Acid-forming 



Oxygen O 16 2 Acid-forming 



Phosphorus P 31 3,5 Acid-forming 



Platinum Pt 195 4 Base-forming 



Potassium K 39 I Base-forming 



Silicon Si 28 4 Acid-forming 



Silver Ag 108 i Base-forming 



Sodium Na 23 i Base-forming 



Sulfur S 32 2,4 Acid-forming 



Tin Sn 119 2,4 Base-forming 



Zinc Zn 65.5 2 Base-forming 



16. Formulas of Compounds. Since compounds are 

 composed of elements, it is possible, by means of combi- 

 nation of symbols, to express the formula of a compound. 

 The formula of a compound denotes the number and 

 kinds of elements contained ; as, for water, the formula 

 H 2 O designates that the compound is composed of the 

 two elements hydrogen and oxygen ; and for sugar, the 

 formula C 12 H 22 O n denotes that the compound is made up 

 of three elements, carbon, hydrogen, and oxygen. The 

 formula always expresses the composition. In the for- 

 mulas of compounds, figures are made use of, as 2 in H 2 O, 

 at the right of the H and partially below the line. In 

 this formula, the 2 indicates that there are two atoms of 

 H in the molecule. In the case of sugar, the figures used 

 mean that in one molecule of sugar there are 1 2 atoms of 

 C, 22 atoms of H, and n of O. The formula of a com- 

 pound always represents one molecule of the compound 

 unless some figure is placed to the left of the formula, as 

 2H 2 O. When placed in this position, the 2 designates 



