. Soil physics and management. roxide in the flask G. The combustion takes place in flaskF, into which about ten grams of soil are placed, together with five to ORGANIC CONSTITUENTS OF SOILS 155 ten grams of pulverized potassium biclirornate. II is a contains a saturated solution of silver sulfate to absorb any hydro-chloric acid, sulphur trioxide or dioxide that may be generated. Bcontains concentrated sulfuric acid, C potassium hydrate, D acidto be weighed with C in determining the weight of carbon acid guard bulb completes the train. The air is allowed topass through
. Soil physics and management. roxide in the flask G. The combustion takes place in flaskF, into which about ten grams of soil are placed, together with five to ORGANIC CONSTITUENTS OF SOILS 155 ten grams of pulverized potassium biclirornate. II is a contains a saturated solution of silver sulfate to absorb any hydro-chloric acid, sulphur trioxide or dioxide that may be generated. Bcontains concentrated sulfuric acid, C potassium hydrate, D acidto be weighed with C in determining the weight of carbon acid guard bulb completes the train. The air is allowed topass through the system for about ten minutes. The soil andpotassium bichromate are thoroughly mixed in F and concentratedsulfuric acid (specific gravity ) slowly admitted through thedropping funnel until the end of the tube from G is covered. Ifno vigorous action takes place the flask may then be slowly heating should continue from five to ten minutes. The bulbsC and D are then weighed and the amount \ of carbon dioxide de-. —Arrangement of apparatus for determining organic matter by chromic acid method.(Bulletin 24, Bureau of Soils.) termined. The organic matter is found by multiplying this by method does not seem to give complete combustion. A com-parison with, combustion method shows that the amount ofcarbon found by oxidation with chromic acid is about per centof that found by the combustion method. Carbon Found by the Two Methods in Soils Dried at 100° C.^^ Kind of sail Combustion methodwith oxygen Chromic acidmethod I per cent Old pasture i New pasture I Arable soil Subsoil per cent 156 SOIL PHYSICS AND MANAGEMENT Determination of Humus/-—Ten grams of soil are treatedon a lilter successively with a one per cent solution of hydro-chloric acid until the lime is removed, as shown by testing afew cubic centimeters of the filtrate with annnouium oxalate afterneutralizing with ammonia. W-asli the soil w
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