ELEMENTARY ANALYSIS. 241 



glass vessels, containing the substances named, are weighed 

 separately after having been filled. Upon heating the com- 

 bustion-tube in a suitable furnace, the organic matter is burnt 

 by the oxygen of the cupric oxide, the hydrogen is converted 

 into water (steam), which is absorbed by the calcium chloride, 

 and the carbon is converted into carbon dioxide, which is absorbed 

 by the potassium hydrate. Upon reweighing the two absorbing 

 vessels at the end of the operation, the increase in weight will 

 indicate the quantity of water and carbon dioxide formed during 

 the combustion, and from these figures the amount of carbon 

 and hydrogen present in the organic matter may easily be cal- 

 culated. 



For instance : 0.81 gram of a substance having been analyzed, 

 furnishes, of carbon dioxide 1.32 gram, and of water 0.45 gram. 

 As every 44 parts by weight of carbon dioxide contain 12 parts 

 by weight of carbon, the above 1.32 gram contains of carbon 

 0.36 gram, or 44.444 per cent. As every 18 parts of water 

 contain 2 parts of hydrogen, the above 0.45 gram consequently 

 contains 0.05 gram, or 6.172 per cent. 



Oxygen is scarcely ever determined directly, but generally 

 indirectly, by determining the quantity of all other elements 

 and deducting their weight, calculated to percentages from 100. 

 The difference is oxygen. 



In the above instance, 44.444 per cent, of carbon and 6.172 

 per cent, of hydrogen were found to be present, and all other 

 elements, except oxygen, to be absent. The quantity of oxygen 

 is, then, equal to 49.383 per cent, and the composition of the 

 substance as follows : 



Carbon, 44. 444 per cent. 

 Hydrogen, 6.172 " 

 Oxygen, 49.384 " 



100.000 



Instead of burning the organic substance by means of cupric 

 oxide, the combustion may be effected by passing dry oxygen 

 gas over the substance heated in a glass tube and collecting 

 the products of combustion as described above. 



Determination of nitrogen. Nitrogen is generally determined 

 by heating the substance with soda-lime and passing the gen- 



16 



