ELEMENTAR Y ANAL YSIS. 283 



Determination of sulphur and phosphorus. These elements are 

 determined by mixing the organic substance with sodium carbonate 

 and nitrate, and heating the mixture in a crucible. The oxidizing 

 action of the nitrate converts all carbon into carbon dioxide, hydrogen 

 into water, sulphur into sulphuric acid, phosphorus into phosphoric 

 acid. The latter two acids combine with the sodium of the sodium 

 carbonate, forming sulphate and phosphate of sodium. The fused 

 mass is dissolved in water, and sulphuric acid precipitated by barium 

 chloride, phosphoric acid by magnesium sulphate and ammonium 

 hydroxide and chloride. From the weight of barium sulphate and 

 magnesium pyrophosphate the weight of sulphur and phosphorus is 

 calculated. 



Determination of atomic composition from results obtained 

 by elementary analysis. The elementary analysis gives the quan- 

 tity of the various elements present in percentages, and from these 

 figures the relative number of atoms may be found by dividing the 

 figures by the respective atomic weights. For instance : The analysis 

 above mentioned gave the composition of a compound, as carbon 

 44.444 per cent., hydrogen 6.172 per cent., and oxygen 49.384 per 

 cent. By dividing each quantity by the atomic weight of the respec- 

 tive element, the following results are obtained : 



44.444 



12 

 6.172 



I 



49.384 

 16 



== 3.703 

 = 6.172 

 = 3.087 



The figures 3.703, 6.172, and 3.087, represent the relative number 

 of atoms present in a molecule of the compound examined. In order 

 to obtain the most simple proportion expressing this relation, the 

 greatest divisor common to the whole has to be found, a task which 

 is sometimes rather difficult on 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 ' 



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 O 5 . 



Empirical and molecular formulas. A chemical formula is 

 termed empirical when it merely gives the simplest possible expression 



