26 



EXPERIMENTAL GENERAL SCIENCE 



part of all sand, sandstone, and quartz rocks. Aluminum is 

 present in clay, and calcium is a necessary component of all 

 limestone rocks. Crystalline carbon forms the diamond, and 

 crystalline aluminum with oxygen forms the ruby, emerald and 

 sapphire. Corundum, or emery, is an impure form of the 

 crystalline state of this compound. The more common chem- 

 ical elements are given in the accompanying table : 



31. Chemical Symbols and Formulas. In order to facilitate 

 his work and save time and space in writing, the chemist has an 

 abbreviation for each chemical element, which he uses instead of 

 the name. This is called a chemical symbol. The chemical 

 symbol is usually the initial of the element, but in cases where 

 more than one element have the same initial all but one have a 

 single letter added. Thus C always stands for carbon, while 

 the chemical symbol for calcium is Ca, for copper, Cu, and 

 for chlorine, Cl, No chemical element has more than two let- 



