SOILS. 225 



these consist of quartz and of particles of feldspar, 

 mica, and hornblende arising from the disintegration 

 of different kinds of rock. 



The soil to be examined is collected from different 

 parts of the field, well powdered, allowed to dry in the 

 air, and uniformly mixed. 



It is most convenient to determine the greater num- 

 ber of the constituents in separate portions of the soil. 



I. Water. A weighed portion of air-dried soil is 

 heated to 100, and retained at that temperature till its 

 weight is constant. In this way the amount of hygro- 

 scopic water is ascertained. 



In order to determine the combined water in the 

 salts, clay, &c., the soil may be heated to 200 or 300, 

 when the ammonia also may be expelled. 



II. Organic matters. The dry soil is ignited with 

 access of air, moistened with carbonate of ammonia, 

 and again heated nearly to redness. The loss in 

 weight (ammonia and nitric acid being taken into ac- 

 count) indicates the total amount of organic matter. 



The amount of nitrogenized organic matter can only 

 be determined by ultimate analysis, when the ammonia 

 and nitric acid must not be neglected in the calcula- 

 tion. 



Certain organic substances, such as fatty and resinous 

 matters, may be extracted from the dried soil by hot 

 alcohol and ether. 



The humous substances may be extracted by boiling 

 the soil with solution of potassa; they are separated, 

 though not completely, from the brown filtered solution, 

 in the form of a brown precipitate, on adding hydro- 

 chloric acid. 



III. Ammonia. The soil is distilled with solution 

 of soda, and the ammonia collected and determined as 

 in No. 5. 



IV. Nitric acid. The analyst must be satisfied with 

 the qualitative detection of nitric acid. The soil is ex- 



