242 CONSIDERATION OF CARBON COMPOUNDS. 



erated ammonia gas through hydrochloric acid, contained in a 

 suitable glass vessel. Upon evaporation of the acid in a weighed 

 platinum dish over a water bath, ammonium chloride is left, 

 from the weight of which compound the quantity of nitrogen 

 may be calculated. 



Determination of sulphur and phosphorus. These elements are 

 determined by mixing the organic substance with sodium car- 

 bonate 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, phos- 

 phorus into phosphoric acid. The two latter 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 hydrate and chloride. 

 From the weight of barium sulphate and magnesium phosphate, 

 the weight of sulphur and phosphorus is calculated. 



Determination of atomic composition from results obtained by 

 elementary analysis. The elementary analysis gives the quantity 

 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 com- 

 pound, 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 respective element, the following results 

 are obtained : 



44.444 



12 



6.172 

 1 



49.384 

 16 



= 3.703 

 = 6.172 

 = 3.087 



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

 numbers of atoms present in a molecule of the compound ex- 

 amined. In order to obtain the most simple proportion express- 

 ing this relation, the greatest divisor common to the whole has 

 to be found, a task which is sometimes rather difficult on 



