ORGANIC CONSTITUENTS OF SOILS 



155 



ten grams of pulverized potassium bichromate. // is a condenser. 

 A contains a saturated solution of silver suli'ate to absorb any hydro- 

 chloric acid, sulphur trioxide or dioxide that may be generated. B 

 contains concentrated sulfuric acid, (' potassium hydrate, D acid 

 to be weighed with C in determining the weight of carbon dioxide. 

 An acid guard bulb completes the train. The air is allowed to 

 pass through the system for about ten minutes. The soil and 

 potassium bichromate are thoroughly mixed in F and concentrated 

 sulfuric acid (specific gravity 1.83) slowly admitted through the 

 dropping funnel until the end of the tube from G is covered. If 

 no vigorous action takes place the flask may then be slowly heated. 

 The heating should continue from five to ten minutes. The bulbs 

 C and D are then weighed and the amount of carbon dioxide de- 



Fm.79. Arrangement of apparatus for determining organic matter by chromic arid method. 

 (Bulletin 24, Bureau of Soils.) 



termined. The organic matter is found by multiplying this by 0.47 1. 

 This method does not seem to give complete combustion. A com- 

 parison with the dry combustion method shows that the amount of 

 carbon found by oxidation with chromic acid is about ?!>.9 per cent 

 of that found by the combustion method. 



Carton Found by the Two Mr'hods in Soils Dried ni ICXf f. 1! 



