20 SCIENCE AND SOIL 



all be derived from the corresponding hydroxids by subtracting 

 water (H 2 O), thus: 



C1(OH) 8 yields OC1OH and H 2 O. 

 C1(OH) 6 yields O 2 C1OH and 2 H 2 O. 

 C1(OH) 7 yields O 3 C1OH and 3 H 2 O. 

 S(OH) 4 yields OS(OH) 2 and H 2 O. 

 S(OH) 6 yields O 2 S(OH) 2 and 2 H 2 O. 



(Sulfur hexahydroxid) (Sulfuric acid) (Water) 



/ . , , O V:/OH 



HO><OH yidds and 



HO/ 



Acids, alkalis (bases) , and salts. The most important chemical 

 elements may be divided into three great groups: 



First, the six metals (iron, aluminum, calcium, magnesium, 

 potassium, sodium); second, the six nonmetals (nitrogen, phos- 

 phorus, sulfur, carbon, silicon, chlorin) ; and, third, the two special 

 elements, oxygen and hydrogen. When combined with oxygen and 

 hydrogen, the six metals form alkaline, or basic, compounds, 

 while the six nonmetals form acid compounds, as shown above. 



Alkali and acid are exactly opposite terms. An acid is sour, 

 while an alkali is sweet (chemically speaking). A better expression 

 than sweet is basic, which means the chemical opposite of sour. 

 Thus, if the land becomes sour because of the development of acids 

 in the soil, we may make it sweet by adding a basic substance 

 like calcium hydroxid, Ca(OH) 2 . This compound is slacked lime. 

 The use of limestone and other forms of lime for correcting soil 

 acidity is fully explained in the following pages. 



Ca(OH) 2 and S(OH) 6 are both hydroxids, but the first is a 

 strong base (or alkali) and the other is a strong acid. When they 

 are brought together, a chemical reaction occurs and the products 

 are neither acid nor basic, but neutral. The sulfur hydroxid 

 S(OH) 6 may also be called hexahydroxyl sulfuric acid. It is often 

 written H 6 SO 6 but it should be borne in mind that, in the structure 

 of the molecule, oxygen is the middle link. If this is heated, or 



