THE CHEMICAL COMPOSITION OF SOILS 



uniting them to form one sample. Samples of subsoil 

 also are taken from the same places. There is usually 

 a sharp line of demarca- 

 tion between the surface 

 soil and subsoil. It is the 

 aim to secure in each case 

 as representative a sample 

 as possible. All coarse 

 stones and roots are re- 

 moved and a record is made 

 of the amount of these. 

 The soil is air-dried, the 

 hard lumps are crushed, 

 and the material mixed and 

 passed through a sieve with 

 holes 0.5 mm. in diameter. 

 Only the fine earth is used 

 for the chemical analysis. 



102. Analysis of Acid- 

 soluble Extract of Soils. 

 Ten grams of soil are 

 weighed into a soil diges- 

 tion flask, and locc. hydro- FIG. 25. 

 chloric acid (sp. gr. 1.115) 



Soil Flask and Acid Diges- 

 tion of Soils. 



are added for every gram of soil used. The soil digestion 

 flask is then placed in a hot-water bath and the digestion 

 carried on for twelve to thirty-six hours at the temperature 

 of boiling water. 25 After digestion is completed the 



