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PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Complete Decomposition. The complete analysis of the soil 

 ib made in two ways: 



First Method. The soil is fused with a mixture of sodium 

 carbonate and potassium carbonate. The silica unites with the 

 soda or potash, forming silicates ; oxides or carbonates are 

 formed from the bases. On treatment with water and acids, the 

 carbonates and oxides dissolve. The silica can easily be separated 

 and the bases determined in the solution. If potash or soda is 

 to be estimated, they must be brought into solution by some other 

 method, such as that named below, or by fusing the silicate with 

 lime. 



Second Method. The soil is treated with hydrofluoric acid, 

 until the silicate is completely dcomposed and the silica driven 

 off as gaseous silicon fluoride SiF 4 . The residue is then dis- 

 solved in acids, and subjected to analysis. The estimation of the 

 silica, if desired, is accomplished by the first method. 



Complete decomposition of a soil shows the constituents which 

 are locked up in the most refractory silicates, as well as those 

 which are easily affected by plants. So far as the writer has been 

 able to find, there have been no investigations made as to the 

 relation of the complete analysis of the soil to its wearing 

 qualities, or needs for plant food. The utmost information such 

 analysis provides at present, is the amount of plant food which 

 may some day become available. 



The complete analysis of some groups of soils is shown in the 

 following table, compiled from Bulletin No. 54 of the Bureau of 

 Soils : 



COMPLETE COMPOSITION OF SOME SOIL GROUPS, PER CENT. 



Relation to Sizes of Particles. Chemical analysis of the differ- 

 ent grades of particles have not always given the same result, but 



