ELEMENTARY ANALYSIS. 243 



account of slight errors made in the quantitative determination 

 itself. In the above case, 0.6172 is the greatest divisor, which 

 gives the following results : 



3.703 6.172 3.087 _ 



rv7 " 



0.6172 0.6172 0.6172 



The simplest numbers of atoms are, accordingly, carbon 6, 

 hydrogen 10, oxygen 5, or the composition is C 6 H 10 5 . 



Empirical and molecular formulas. A chemical formula is termed 

 empirical, when it merely gives the simplest possible expression 

 of the composition of a substance. In the above case, the 

 formula C 6 H 10 O 5 would be the empirical formula. It might, 

 however, be possible that this formula does not represent the 

 actual number of atoms in the molecule, which might contain, 

 for instance, twice or three times the number of atoms given, in 

 which case the true composition would be expressed by the 

 formula C 12 H 20 10 or C^H^O^. 



If it could be proven that one of the latter formulas is the 

 correct one, it would be termed the molecular formula, because it 

 expresses not only the numerical relations existing between the 

 atoms, but also the absolute number of atoms of each element 

 contained in the molecule. 



The best method to determine the actual number of atoms 

 contained in the molecule is the determination of the specific 

 weight of the gaseous compound, taking hydrogen as the unit. 

 For instance : The analysis of a liquid substance gave the fol- 

 lowing result: 



Carbon, 92 308 per cent. 

 Hydrogen, 7.692 " 



100.000 



From this result the empirical formula, CH, is deducted by 

 applying the method stated above. If this formula were also 

 the molecular formula, the density of the vapors of the sub- 

 stance would, when compared with hydrogen (according to the 

 law of Avogadro), be equal to 6.5, because a molecule of hydrogen 

 weighs 2 and a molecule of the compound CH weighs 13. 



Suppose, however, the density of the gaseous substance is 



