1913] 



Burgess: Beduction Methods for Soil Nitrates 



57 



TABLE 11— (Continued) 

 Effects of "Mixed Alkali" Salts 



Salts 

 added 

 Grams 

 0.2 NaCl 



0.35 NaoS04 



0.1 NaoCO, 



r 



0.2 NaCl 

 0.35 Na.lSOi 

 0.1 Na.COa J 



0.2 NaCl ] 

 0.35 Na.SOi }. 

 0.1 Na,C03 J 



100 



50 



25 



99.54 



50.05 



24.57 



65.00 



33.00 



12.00 



That the salts present have little effect on the accuracy of 

 the determination by the reduction method, and the superiority 

 of the latter over the phenoldisulphonic acid method, is clearly 

 shown by a comparison of the last two columns in the foregoing 

 table. Where large losses of nitrates are induced by the presence 

 of NaCl and NaoSO^ with the second named method, there are 

 only slight losses when the reduction method is employed, and 

 these are found by a comparison with Table I to be apparently 

 due to other causes. 



In most cases where the reduction method is used there are 

 slight losses of ammonia, although in a few individual analyses 

 all of the nitrogen was recovered. It may be stated here that 

 several analyses were run on solutions containing 100 mgs. of 

 nitrate nitrogen, placing rubber stoppers in the large reducing 

 test tubes, carrying bent glass tubes as traps and connecting with 

 test tubes containing 10 c.c. of N/10 HCl each. These were later 

 titrated against N/10 NH^OH and the results added to the figures 

 found by distillation. By using this extra process we were 

 able to recover all the N as NHg, but it was not found to be 

 necessary where the smaller amounts of nitrate were present. 

 It should be remembered that in soil work over 30 mgs. of nitrate 

 nitrogen per 100 grams of soil are infrequently found, and of 

 this amount only an aliquot (one-half) is taken for the actual 

 analysis. In nitrification work also, especially where the pro- 

 duction of nitrates is intense, the difference between parallels is 



