117 



T\m i \.-Comparison of sodium peroxid fusion and magnesium nitrate methods for 



total phosphorus. 



[Water-free basis.] 



Duplicates not reported. 



Tlu n-foriM' did not ask that these methods be checked by the carbonate fusion or 

 standard method, a. it is sometimes called, his work with the method having shown 

 that it has the disadvantage of a large amount of soluble silica, necessitating dehy- 

 dration, and in the cane of a soil with any considerable amount of organic matter 

 there exist favorable conditions for reduction and, consequently, some loss of 

 phosphorus. 



In Table 2 will be found the results of the referee's determination of total phos- 

 phorus in the two soils, working as follows: Making a carbonate fusion, then proceeding 

 as for an accurate determination of silica, the silica evaporated with hydrofluoric acid, 

 the residue taken up with hot, strong hydrochloric acid and added to the filtrate 

 from the silica. Iron, alumina, and phosphorus precipitated with ammonium 

 hydroxid, washed, redissolved, and the phosphorus determined volurnetrically, as 

 in the magnesium nitrate method. 



It will be seen from the table that in Soil I, containing very little organic matter, 

 the results compare very favorably with the other methods, but in Soil II, rich in 

 organic matter, the average is lower. 



