CONSTITUTION OF MATTER 



cubic centimeters of distilled water. The combined 

 amounts of the two liquids is one hundred cubic centi- 

 meters. But if the burette is closed and the two liquids 

 thoroughly mixed there will be 

 found but about ninety-eight cubic 

 centimeters of the mixture. From 

 observations such as these, scientists 

 were led to investigate the consti- 

 tution of matter. If a mixture of 

 equal quantities of two substances 

 is less than their combined amounts, 

 surely the substances must have 

 gone into each other. To do this, 

 however, the substances must have 

 particles and spaces, and the par- 

 ticles of one must have moved into 

 the spaces of the other. So rea- 

 soned the early scientists, and the 

 result of their reasoning is the 

 "Molecular Theory of Matter." 

 which explains the constitution of 

 matter. 



Molecular theory. According to this theory every- 

 thing in nature is composed of very tiny particles with 

 spaces between them. The particles are called mole- 

 cules and the spaces between the molecules are called 

 inter-molecular spaces. The molecules are conceived as 

 being in constant motion back and forth in the inter- 

 molecular spaces. In the same substance, all molecules 



Fig. 3. If water 

 and alcohol are 

 mixed, the two 

 liquids occupy less 

 space than when 

 they are kept sepa- 

 rate. 



