SOILS AND FERTILIZERS 



easily soluble phosphoric acid is dissolved, and this 

 readily allows fertilized and unfertilized soils to be 

 distinguished. By the use of dilute organic acids and 

 salts decided differences have been shown between soils 

 fertilized and unfertilized with potash. 26 



92. Sampling of Soils. A composite sample of 

 soil is obtained from a field by taking several small 

 samples to a depth of 6 to 9 inches, from different 

 places, and uniting them to form one sample. Samples 

 of subsoil also are taken from the same places. There 

 is usually a sharp line of demarkation between the 

 surface and subsoils. It is the aim to secure in both 

 cases as representative samples as possible. All 

 coarse stones and roots are removed and a record is 

 made of the amount of these materials. The soil is 

 air-dried, the hard lumps are crushed, and the mate- 

 rials mixed and passed through a sieve 

 with holes 0.5 mm. in diameter. Only 

 the fine earth is used for the chemical 

 analysis. 



93. Analysis of Acid- soluble Ex- 

 tract of Soils. Ten grams of soil are 

 weighed into a soil digestion flask, 

 and 10 cc. hydrochloric acid (sp. gr. 

 1.115), 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 hours 

 Fig. 19. Diges- at the temperature of boiling water. 27 

 tion flask. After digestion is completed the con- 

 tents of the flask are transferred to a filter and separated 



