CHEMISTRY SINCE TIME OF DALTON 



From the outset the idea had had the utmost tangi- 

 bility in the mind of Dal ton. He had all along rep- 

 resented the different atoms by geometrical symbols 

 as a circle for oxygen, a circle enclosing a dot for hy- 

 drogen, and the like and had represented compounds 

 by placing these symbols of the elements in juxtapo- 

 sition. Berzelius proposed to improve upon this 

 method by substituting for the geometrical symbol the 

 initial of the Latin name of the element represented 

 O for oxygen, H for hydrogen, and so on a numerical 

 coefficient to follow the letter as an indication of the 

 number of atoms present in any given compound. 

 This simple system soon gained general acceptance, 

 and with slight modifications it is still universally 

 employed. Every school-boy now is aware that H 2 O 

 is the chemical way of expressing the union of two 

 atoms of hydrogen with one of oxygen to form a mole- 

 cule of water. But such a formula would have had 

 no meaning for the wisest chemist before the day of 

 Berzelius. 



The universal fame of the great Swedish authority 

 served to give general currency to his symbols and 

 atomic weights, and the new point of view thus devel- 

 oped led presently to two important discoveries which 

 removed the last lingering doubts as to the validity 

 of the atomic theory. In 1819 two French physicists, 

 Dulong and Petit, while experimenting with heat, dis- 

 covered that the specific heats of solids (that is to say, 

 the amount of heat required to raise the temperature of 

 a given mass to a given degree) vary inversely as their 

 atomic weights. In the same year Eilhard Mitscher- 

 lich, a German investigator, observed that compounds 



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