148 ORGANIC AGRICULTURAL CHEMISTRY 



by oxidation into gaseous or volatile products which disappear, 

 while the inorganic constituents are converted into nonvolatile 

 compounds which remain. Thus, generally speaking, the 

 organic constituents yield volatile products on burning, and the 

 inorganic constituents yield nonvolatile. 



If we were dealing with pure organic constituents by them- 

 selves, such as pure carbohydrates, fats or proteins, we should 

 find this to be wholly true. On burning in air the carbon would 

 be converted into carbon dioxide gas, CO2, the hydrogen into 

 water, H2O, the nitrogen into free nitrogen, N, the sulphur would 

 yield the gas sulphur dioxide, SO2, and the phosphorus would be 

 oxidized to phosphorus pentoxide, P2O5, a solid. All of these 

 products, whether gases, liquids or solids, would be volatilized 

 at the temperature of the combustion and would thus disap- 

 pear. In a like manner the pure inorganic constituents by 

 themselves would be left on burning in the form of oxides, 

 carbonates, chlorides, sulphates, nitrates or phosphates, depending 

 largely upon the original form in which they were present. 



However, on burning any mixed plant or animal material 

 the two sets of products are present together and a sharp sepa- 

 ration does not take place. All of the hydrogen of the organic 

 constituents disappears in the form of water vapor. A large 

 part of the carbon likewise goes off as carbon dioxide gas. 

 Some of the carbon dioxide, however, which is formed from the 

 carbon of organic compounds, in the presence of the metallic 

 elements of the inorganic constituents, unites with the oxides 

 of these metals and remains as nonvolatile carbonates, e.g. 

 potassium carbonate, K2CO3. The sulphur and nitrogen also, 

 instead of being completely volatilized, combine with the metal 

 oxides as sulphates and nitrates, e.g. sodium sulphate, Na2S04, 

 potassium nitrate, KNO3. Likewise, the phosphorus from 

 organic compounds will not volatilize, but will remain non- 

 volatile as a phosphate of some metal, e.g. calcium phosphate, 

 Ca3(P04)2. Also any iron, calcium or other metallic element, 

 although present as part of a true organic compound, will re- 

 main after combustion in the form of some nonvolatile salt. 



