CHEMISTRY AND HEAT 



Symbols and Formulas. Each of the known elements is 

 designated by a symbol, which is a letter or a pair of letters, 

 oftentimes the initial letter of the name of the element. Thus, 

 O is the symbol for oxygen, H for hydrogen, C for carbon, and 

 so on. When two or more elements unite to form a compound, 

 the symbols representing the elements in the compound may 

 be connected in a formula, which will show how the atoms of 

 the elements combined to form the compound. Thus, H and 

 O are the symbols of the elements hydrogen and oxygen. 

 When these two gases unite in certain proportions, they form 

 water, a compound whose formula is HiO. This formula 

 indicates, first, that water is composed of hydrogen, H, and 

 oxygen, O; and second, it indicates, by the subscript 2, that 2 

 atoms of hydrogen unite with 1 atom of oxygen to form 1 



ATOMIC WEIGHTS OF ELEMENTS 



molecule of water. The formula for carbon dioxide is COi, 

 which indicates that a molecule of carbon dioxide consists of 

 1 atom of carbon, C, and 2 atoms of oxygen, O. 



Atomic Weight and Molecular Weight. The ratio between 

 the weight of an atom of any element and the weight of an 

 atom of hydrogen is termed the atomic weight of that element. 

 The symbols and the atomic weights of a number of the ele- 

 ments most commonly met with in steam engineering are 

 given in the accompanying table. By the aid of the atomic 

 weights, the composition of any substance, by weight, may be 

 determined. For example, water contains 2 atoms of hydrogen 

 and 1 atom of oxygen. Multiplying the number of atoms of 

 each by the atomic weight, it is seen that there are 2X1=2 

 parts of hydrogen, by weight, and, IX 16= 16 parts of oxygen, 



