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RELATIONS BETWEEN THE STRUCTURE AND BEHAVIOR OF 

 MATTER 



We have seen that matter is composed of exceedingly minute 

 particles called molecules. Just as we can thoroughly understand 

 the behavior of a watch or an automobile engine only if we know 

 the details of its structure, and how the parts work, so we can 

 understand the physical and chemical behavior of matter in masses 

 only if we are familiar with its ultimate mechanism. Hence, we 

 must now take up the structure of matter in its three states, the 

 gaseous, the liquid, and the crystalline (or solid). In doing this, 

 we shall keep constantly in view the connection between the molec- 

 ular relations and the general behavior of the matter. 



The Properties of Gases. The most remarkable thing about 

 a gas, considering the looseness with which its material is packed, 

 is the total absence in it of any tendency to settling or subsidence. 

 Since the molecules cannot be at rest upon one another, as the 

 great compressibility shows, we are driven to conclude that they 

 are widely separated from one another, and that they occupy the 

 space, otherwise a complete vacuum, by constantly moving about 

 in all directions. But a moving aggregate of particles which 

 does not even finally settle must be in perpetual motion. We must, 

 therefore, believe the molecules to be wholly unlike larger particles 

 of matter in having perfect elasticity, in consequence of which 

 they undergo no loss of energy after a collision. They must 

 continually strike the walls of the vessel and one another and re- 

 bound, yet without loss of motion. The fact that each gas is 

 homogeneous, efforts to sift out lighter or heavier samples having 

 failed, requires the supposition that all the molecules of a pure 

 gas are closely alike. 



The diffusibility of gases is due to the motion of the molecules, 

 and their permeability to the space available to receive molecules 

 of another gas. These two modes of behavior involve no addi- 

 tional molecular properties. The word " diffusion " is often 



