374 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 

 the numbers of atoms are in the proportion 



c H _ o or 



I2*OO I'OOS IO 



C 6-06 H 5-43 O 1-36. 



Dividing by the smallest number, these proportions become 



C 4-46 H 3-99 O i, 



or yery nearly 



C 4^ H 4 O i. 



Multiplying by two in order to remove fractions, the 

 simplest empirical formula for the compound is seen to be 

 C 9 H 8 O 2 . The composition calculated for this formula is 



C 72-94 H 5-45 O 21-61 



and agrees closely with the composition found by com- 

 bustion. The MOLECULAR FORMULA, which should express 

 both the composition and the molecular weight of cinnamic 

 acid, is [C 9 H 8 O 2 ] ? j., where n is an integer, the value of which 

 must be determined by other methods, e.g. from the chemical 

 properties of the acid or from the boiling-points and freezing- 

 points of its solutions. 



Empirical formulae of metallic salts. The following 

 examples show how the composition and the empirical 

 formulae of some typical metallic salts have been determined. 

 The analytical data are taken from Berzelius's 1 papers on 

 Fixed Proportions, 1811 1812 (Ostwald's Klassiker, 

 No. 35). The atomic weights are substantially those of Stas. 



i. Lead oxide, sulphide and sulphate. Berzelius found 

 (Fixed Proportions, 1811-1812; Klassiker, XXXV, 6-13) 

 that : 



1 In quoting Berzelius's data it has been necessary to distinguish 

 between the actual analyses, and the compositions which he calculated 

 on the assumption that both chlorine and nitrogen were not elements 

 but oxides. 



