Chemical Change and Energy 297 



FIG. 161. Water can be separated into two gases by a current of electricity. 



The quick way chemists write about elements. Since 

 everything in the world is made of a combination or 

 a mixture of elements, chemists have found it very 

 convenient to make abbreviations for the names of the 

 elements so that they can quickly write what a thing 

 is made of. They indicate hydrogen by the letter H. O 

 always means oxygen to the chemist ; C means carbon ; 

 and Cl means chlorine, the poison gas so much used in 

 the World War. The abbreviation stands for the Latin 

 name of the element instead of for the English name, 

 but they are often almost alike. The Latin name for 

 the metal sodium, however, is natrum, and chemists 

 always write Na when they mean sodium; this is for- 

 tunate, because S already stands for the element sulfur. 

 Fe means iron (Latin, ferrum). But I stands for the 



