PRACTICE XXX 



DETERMINATION OF ORGANIC CARBON IN SOILS 



Place 2 g. of an ordinary soil (or 0.5 g. of a peaty soil), 10 g. of 

 sodium peroxid (as free as possible from carbonate), and, depending 

 upon the amount of organic matter present, from 0.7 to 1 g. of very 

 finely powdered magnesium (to start the combustion) in a Parr 1 

 explosion bomb. Close the bomb, mix the contents thoroughly by 

 shaking, place bomb in a vessel of water so that only the stem pro- 

 jects through a hole in the bottom of a tin can inverted over the 

 vessel of water, and explode by means of a hot iron plug or an elec- 

 tric current. Bring the contents of the bomb into a beaker with a 

 stream of hot water, boil a few minutes with the beaker covered, 

 and, by means of the separately funnel, bring into the Erlenmeyer 

 flask of the apparatus. Liberate the C0 2 with dilute (1 : 2) sulfuric 

 acid, boiling finally, measure the volume of the gas > absorb the 

 C0 2 in a gas pipette containing a 33 per cent solution of potassium 

 hydroxid, and measure the unabsorbed gas. Note the temperature 

 and pressure, and calculate the organic carbon. 



cc. of CO 2 



Bar., Temp. 



Weight of C 



Weight of C in peroxid 



Weight of total C in soil 



Per cent of total C 



Per cent of inorganic C 



Per cent of organic C 



1 Journal American Chemical Society, Vol. 26, pp. 294, 1640. 



66 



