Size of Molecules. 9 



sun the greater tension which is developed is due to the 

 fact that the absorption of heat causes all the molecules 

 to travel faster, and, traveling faster, they must exert a 

 greater pressure whenever collision occurs and their motion 

 is arrested. 



It has been computed that the mean rate at which the 

 molecules of hydrogen gas travel at ordinary temperature 

 and atmospheric pressure is some 6,000 feet per second. 

 Under the same conditions molecules of oxygen gas which 

 are 16 times as heavy travel only one-fourth as rapidly. 



If it is difficult to think of a body like a horse-shoe or 

 a hammer maintaining its form against great strains when 

 the molecules composing it are neither at rest nor in con- 

 tact it may be helpful to recall the conditions which exist 

 in the solar system. Here we have the sun with all its 

 planets and their satellites, together with asteroids, comets 

 and meteors, each in rapid motion but separated by im- 

 mense distances, and yet the whole system constitutes one 

 gigantic body maintaining persistently its form as it moves 

 through space. 



6. The Size of Molecules. Molecules are so very small 

 that it is extremely difficult to form any just conception 

 of them, yet there are many experiments and observations 

 which prove them very minute. Nobert, for example, 

 ruled parallel lines on glass at the rate of 101,600 per 

 linear inch, proving that the point of the diamond which 

 plowed the furrows must have been far less than TOO^ ,,i of 

 an inch in diameter. 



Lord Kelvin has computed that the number of molecules 

 in a cubic inch of any perfect gas under a temperature 

 of 32 F. and a pressure of 30 inches of mercury must be 

 as great as 10 23 or ten sextillions. 



This is an enormous number, but that there is a proba- 

 bility of truth in it may be demonstrated by a simple ex- 

 periment. 



Dissolve .05 of a gram of aniline violet in alcohol and 

 distribute it through 500 cu. in. of water in a large glass 



