94 



THE PHYSICAL PROPERTIES OF SOILS 



for about ten minutes or until the combustion of the 

 organic matter is complete, and then allowed to cool. 

 Care must be taken that a steady stream of air is kept 

 passing through the system. 



The amount of CO2 given off is determined by 

 weighing the potash absorption bulb, and its acid guard 

 bulb, at the beginning, and again at the close of the 

 experiment. In calculating the per cent of organic 



APPARATUS USED FOR THE DETERMINATION OF THE ORGANIC 



MATTER IN SOILS BY THE WET-COMBUSTION METHOD 



(Bulletin No. 24, Bureau of Soils) 



matter in the soil from the weight of CO^ found, it is 

 necessary to use a conversion factor which, multiplied 

 by the weight of the CO2, gives the weight of the or- 

 ganic matter from which the gas was derived. The 

 factor generally accepted for this purpose is 0.471, 

 based upon the investigations of Wollny and his study 

 of the carbon content of the humus of soils. 



Certain modifications of the above method are neces- 

 sary when large quantities of chlorides and carbonates 

 are present in the soil. 



For a full description of the apparatus, and complete 

 details of the method, the student is referred to Bul- 

 letin No. 24, Bureau of Soils. 



