3 02 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Chemical Methods. Chemical methods do not determine the 

 relative availability of the material, but distinguish between sub- 

 stances of high and of low availability. Three methods have been 

 proposed : 



(1) Digest with pepsin hydrochloric acid, filter, wash, and 

 determine nitrogen in the residue. 



(2) Digest 2 with neutral permanganate of potash in a boiling 

 water bath, filter, wash, and determine nitrogen in the residue. 



(3) Distil with caustic soda and permanganate, and determine 

 the ammonia which passes over. 



Each of these methods has its advantages and disadvantages. 

 Method (3) is not applicable to cottonseed meal. All the 

 methods depend on differences in the resistance of the various 

 materials to the reagents employed. 



Influence of Conditions on Availability. Various conditions 

 affect the availability of nitrogen in fertilizers, such as acidity of 

 soils, fineness of division of bone, etc. 



Wheeler, 3 in an unlimed acid soil, found the availability of 

 blood to be 45.5, and ammonium sulphate injurious, while on the 

 same soil limed, their values were 90.3 and 45.5 respectively. 

 Johnson, Jenkins, and Britton 4 tested the availability of nitrogen 

 in bone of different degrees of fineness; for meal less than 1/150 



1 Fraps, Bulletin 106, Texas Station. 



2 See Street, Report Connecticut Exp. Sta., 1911, Fertilizers, p. 9. 



3 Bulletin 53, Rh6de Island Station. 



4 Connecticut State Station Report, 1897, p. 257. 



