74 



SOILS AND FERTILIZERS 



provided with a glass stopper which is connected with 

 a condensing tube. The soil digestion flask is then 



placed in a hot water-bath and the di- 

 gestion is carried on for twelve hours at 

 the temperature of boiling w r ater. After 

 the digestion is completed the contents 

 of the flask are transferred to a filter and 

 separated into an insoluble part, and the 

 acid solution which contains the com- 

 pounds of the various elements. The 

 following table will give a general idea 

 of how the different materials are ob- 

 tained from the acid solution. This table 

 is not intended as an outline for soil 

 analysis, but simply to give the stu- 

 dent of general chemistry an idea of how an analysis 

 is made. 



The second half of the acid solution is divided into 

 three portions. The first portion is used for the deter- 

 mination of phosphoric acid. The acid is precipitated 

 with ammonium molybdate. The second portion is 

 used for determination of sulphuric acid, which is pre- 

 cipitated as barium sulphate. The carbon dioxide 

 is determined on a fresh portion of the original 

 soil ; the acid is liberated with hydrochloric acid 

 and the carbon dioxide is retained by absorbents and 

 weighed. The nitrogen and humus are determined in 

 separate portions of the original soil. 



Fig. 19. Diges- 

 tion flask. 



