174 



OUTLINE OF CHEMICAL STUDY 



199. Compounds. When two or more elements unite 

 with each other in a definite proportion, the new sub- 

 stance formed is called a chemical compound. This will 



be explained more fully later ( 202, 

 203). Note, however, that the ele- 

 ments must be united, that is, not 

 simply lying side by side in the same 

 mass, but the smallest particles of each 

 actually combined with those of the 

 others. Also note that the result is 

 a new substance, unlike either of the 

 elements which compose it; even to 

 its molecules, the compound is differ- 

 ent from either of the elements. 



Water is a chemical compound ; its 

 elements are hydrogen and oxygen 

 both gases. Other common compounds are starch, sugar, 

 alcohol, quartz, and many acids, bases, and salts. 



Experiment 109. Put a small piece of zinc into a little hydro- 

 chloric acid (an inch in a test tube) ; note all that happens. If 

 the zinc does not finally disappear, add more acid. When the 

 zinc can no longer be seen, boil the liquid in an evaporating dish 

 (Fig. 127) till dry. Examine the substance that remains. Do 

 you think this a compound ? Why ? 



200. Mixtures When two or more substances, with- 

 out uniting chemically, together form another substance, 

 that mass is called a mixture. A mixture may differ in 

 some ways from each of the substances that compose it, 

 but no new substance is formed ; that is, the mixture has 

 no molecule of its own, being composed of molecules of 

 each substance lying side by side but not combined. 



FIG. 127 



