CHAPTER II 



THE MORE COMMON ELEMENTS AND COMPOUNDS 



Important elements. Fifteen elements are of special interest and 

 importance in the study of soil fertility, because they are commonly 

 found in plants and animals and because they so largely constitute 

 the soil and air and ocean and the common things of earth. Of 

 these fifteen elements, ten are known to be essential to plant 

 growth; eight of them constitute 98 per cent of the solid crust of 

 the earth; four of them constitute 99.6 per cent of the ocean, about 

 96.4 per cent being water (H 2 O) and 3.2 per cent common salt 

 (NaCl); and two of them (nitrogen and oxygen) constitute 98.5 

 per cent by weight of the dry atmosphere, about 1.5 per cent of 

 the air consisting of the recently discovered element, argon. 



The ten essential elements of plant food may be grouped as 

 follows : 



C, H, O, obtained by plants from air and water. 



P, K, N, sometimes deficient in soils, and of money value as 

 plant food. 



S, Ca, Fe, Mg, required in small amounts and not likely to be 

 deficient in soils. 



The five other elements commonly present in plants are silicon, 

 aluminum, sodium, chlorin, and manganese. 



The reader is earnestly advised to learn by groups 1 the name 

 and atomic weight and the valence of each of these important 

 elements, and the following table is constructed for this purpose. 



Aside from the name, symbol, atomic weight, and valence, 

 Table 2 furnishes some extremely valuable and useful information 

 concerning the occurrence and relative abundance of the elements 

 which essentially constitute the crust of the earth, the ocean, the 

 air, and the agricultural plants and animals. These data are based 



1 The author consents to the students' memory key: "C. HOPK'NS' CaFe,-Mg, " 

 if Mg stands for "Mighty good " and the omission of I, for modesty. 



