2 SCIENCE AND SOIL 



Chemical elements. An element is a substance which cannot be 

 divided into two or more different substances. Sulfur (S) is a 

 solid, nonmetallic element, easily melted to the liquid form. 

 A piece of sulfur may be divided into two parts, but each part is 

 sulfur, and if nothing else is added to sulfur, nothing but sulfur 

 can be obtained from it. Carbon (C) is the principal element con- 

 tained in coal. Iron is a well-known metallic element. Oxygen (O) 

 is an element contained in the air in the gas form. 



Chemical compounds. A[ compound is a substance which con- 

 tains two or more different elements and which possesses some 

 properties or characteristics not possessed by either element 

 alone. Thus, if carbon and sulfur be mixed together at the ordi- 

 nary temperature, the product is only a mixture in which each 

 element retains its own properties; but, at a higher temperature 

 and under proper conditions, one combining weight of black 

 carbon will unite with two combining weights of yellow sulfur 

 and form the compound called carbon disulfid (CS 2 ), which is 

 neither black nor yellow nor solid, but a colorless liquid somewhat 

 resembling water, but which, when pure, contains absolutely noth- 

 ing but the two elements, carbon and sulfur. 



Carbon, in charcoal for example, may be eaten in considerable 

 quantity without harm, and sulfur is not dangerous in large doses; 

 but the compound, carbon disulfid, is a deadly poison, and is fre- 

 quently used as an insecticide and for the extermination of gophers 

 and other burrowing animals. Thus the properties of the com- 

 pound may differ in many respects from those of either element 

 contained in it. 



On the other hand, when carbon is burned, by uniting with the 

 oxygen of the air, the compound, carbon dioxid (CO 2 ), is formed, 

 and when sulfur is likewise burned, the compound, sulfur dioxid 

 (SO 2 ), is formed; while if carbon disulfid is burned, by uniting 

 with the oxygen of the air, the products of combustion are exactly 

 the same as though the carbon and sulfur were burned separately 

 with oxygen, carbon dioxid and sulfur dioxid being formed. 



Sodium (Na, natrium in Latin) is a soft metallic element which 

 takes fire when thrown into water, and the element chlorin (Cl) 

 is a greenish colored poisonous gas, but when united these two 

 elements form the compound called sodium chlorid (NaCl), salt. 



