1913] Burgess: deduction Methods for Soil Nitrates 61 



TABLE VI 



Time of Eeduction 12 Hours. Temperature Constant at 8° to 10° C. 



We thus see that at a temperature of 45^ C. the reduction 

 was more nearly complete in 6 hours than it was at the end of 

 12 hours where the temperature was maintained at 10° C. By 

 means of a series of experiments similar to those shown in Table 

 IV it is readily possible to find the optimum length of time for 

 complete reaction at any given temperature. 



Amount NaOH Solution Required 



By another series of experiments, in which the traps above 

 mentioned were used and different amounts (varying from 1 to 

 5c.c.) of the 50 per cent NaOH solution added, we found that 

 2 c.c. of the latter gave the best results. One e.c. evidently did not 

 generate hydrogen in sufficient quantities for complete reduction 

 (especially in the presence of the larger amounts of nitrate), 

 while the 4 and 5 c.c. portions made the solutions so alkaline as 

 to effect the escape of considerable amounts of ammonia. 



General Remarks 



The results obtained in the experiments described above are 

 considered a valuable contribution to our methods of chemical 

 and biochemical soil analysis, because they establish, on a prac- 

 tical basis, a method for the determination of nitrates in soils 

 which yields accurate results, regardless of the condition of the 

 soil which is examined. While for rapid determinations the 

 reduction method is not found as serviceable as the phenoldisul- 

 phonic acid method, it replaces the latter for work on "alkali" 

 bearing soils where it alone can be safely employed. 



