ON THE EXAMINATION OF SOILS 141 



millimeter sieve should be used when the de- 

 terminations are made on 100 gms. or more of 

 soil. The fine earth is thoroughly mixed and 

 preserved in a tightly stoppered bottle, from 

 which the portions for analysis are weighed. 



The coarse part is weighed and examined 

 microscopically or with Thoulet's solution. 



It may sometimes be necessary to wash the 

 soil through the one-half millimeter sieve with 

 water; but this is to be avoided whenever possible. 



Determination of Moisture. Heat from 2 to 

 5 gms. of the air-dried soil in a flat-bottom, 

 tared platinum dish for five hours in a water 

 oven kept briskly boiling; cover the dish, cool 

 in a desiccator, and weigh. Repeat the heating, 

 cooling, and weighing at intervals of two hours 

 till nearly constant weight is found, and estimate 

 the moisture by the loss of weight. Weigh rapidly, 

 to avoid absorption of moisture from the air. 



Determination of Volatile Matter. Heat the 

 dish and dry soil from the above determination 

 to full redness, until all organic matter is burned 

 away. If the soil contains appreciable quantities 

 of carbonates, the contents of the dish, after 

 cooling, are moistened with a few drops of a 

 saturated solution of ammonium carbonate, dried 

 and heated to dull redness to expel salts of 

 ammonia, cooled in a desiccator, and weighed. 

 The loss in weight represents the organic matter, 

 water of combination, salts of ammonium. 



Determination of Acid-soluble Materials. In the 



