Constitution of Bodies. 



tnre we could neither smell nor taste, for substances must 

 penetrate these sense organs before the sensations are 

 awakened. 



That there is unoccupied space in bodies which appear 

 to have a close structure may be demonstrated with the ap- 

 paratus represented in Fig. 1. The bottle is 

 filled with water and into this is dropped a 

 large crystal of some salt, as potassium ni- 

 trate or sulfate, or 4 teaspoonfuls of granu- 

 lated sugar. When this is done the rubber 

 cork carrying the graduated glass tube is in- 

 serted and crowded down until the water 

 rises in the tube and stands at one of the 

 graduation marks. If any change in volume 

 occurs with the solution of the salt it will be 

 shown by a rise or fall of the water in the 

 tube where the amount of change can be read. 

 The bottle -is placed in a large vessel of 

 water for the purpose of maintaining a con- 

 stant temperature during the experiment. 



The molecules themselves are made up of 

 smaller units which have received the name 

 of atoms and the number of these atoms 

 which enter into the construction of the molecule varies 

 with the substance. In some substances the molecule con- 

 sists of two atoms, as common salt, one of sodium and one 

 of chlorine, while the water molecule contains three atoms, 

 two of hydrogen and one of oxygen. In molecules of cane 

 sugar there are forty-five atoms of three different kinds, 

 carbon, hydrogen and oxygen, and there are many sub- 

 stances having molecules more complex than those of sugar. 



4. Distances Between Molecules Change With the Tem- 

 perature of the Body. A bar of iron lengthens and shortens 

 as its temperature rises and falls, and the wheelwright 

 takes advantage of the fact to set the tires of the wagon. 

 This change of volume with temperature is due to the fact 

 that the mean distance between the molecules becomes 



Fro. 1. 



