CHAPTER IV 



COMPOUNDS, BIOLOGY'S BUILDING MATERIALS 



Vocabulary 



Extinguish, to "put out" a flame. 



Constitutes, composes. 



Converted, changed. 



Emergencies, sudden needs. 



Distinguish, to show differences between. 



Characteristics, properties by which a substance may be known. 



We have learned the names and something about the charac- 

 teristics of a few of the elements. In dealing with these elements 

 and their compounds it is necessary to find some way to distinguish 

 one from another, in order that they may be properly studied. 



Method of " Testing " Substances. Such means of distinguish- 

 ing are called " tests " and we have already referred to one in the 

 case of oxygen. The test consisted in the fact tha,t oxygen, and 

 no other substance, would cause a glowing spark to burst into flame. 



Before taking up any test three things must be considered. 



1. A substance known to be the one we are studying must be 

 tested, so that we may know the correct result, and be able to 

 recognize it in an unknown case. 



2. The test must be true of the substance sought, and of no 

 other. You can readily see, that if even one other gas would kindle 

 the glowing splinter, then that could not be used as a test for oxygen. 



3. The test must be made in the same way, every time, or else 

 one might suppose that the result was affected by the difference 

 in treatment. 



INORGANIC COMPOUNDS 



Carbon Dioxide. When carbon unites with oxygen, it forms a 

 colorless, odorless, and tasteless gas called carbon dioxide (CO 2), 

 which is heavier than air and will extinguish a flame. 



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