CHAPTER I 



EXPLANATIONS AND DEFINITIONS OF SOME CHEMICAL AND 

 PHYSICAL TERMS 



An intelligent discussion of the various functions of the human 

 body cannot be given without some elementary considerations in 

 the field of chemistry and its intimately related science of physics. 

 Probably the briefest method for presenting the essential points 

 is in the way of definitions with accompanying illustrations, and 

 explanations where necessary. 



THE PHYSICAL SCIENCES 



1. Physics deals with mechanics, heat, light, sound, and elec- 

 tricity, and their relations to matter. 



2. Chemistry deals with change in the composition of matter, 

 the energy change involved therein, and the principles controlling 

 chemical change. 



MA^ITER 



1 . Defined. — Matter is usually defined as anything that oc- 

 cupies space, as wood, air, water. 



2, Forms in which matter exists. 



Elements. — An element is a substance which cannot be sepa- 

 rated into more simple substances by any mea'ns known to science 

 at present. Elements are supposed to be made up of atoms which 

 are alike for the same element and cannot be divided. 



There are about eighty of these elements, less than half of 

 which are well known. Some of the most common are carbon, 

 iron, sulphur, mercury, and oxygen. 



Compounds. — A compound is a substance which can be sepa- 

 rated into simpler substances. Compounds are supposed to be 

 made up of molecules which are composed of .groups of atoms. 

 Molecules are alike for the same compound and can be divided, 

 giving elements or simpler compounds. For example, water is 

 composed of hydrogen and oxygen, each molecule having in it 



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