]913] 



Burgess: Beduction Methods for Soil Nitrates 



59 



The Effect of Soluble Organic Materlvlr on the Reduction 



Method 



After having found that the soluble mineral salts had no 

 effect on the accuracy of the reduction method, it was deemed 

 advisable to ascertain whether or not the organic matter, which 

 is always present in the soils to a greater or less extent, interferes 

 with it. Such organic materials may be roughly divided into 

 two great classes: the humates, or the salts of humic acid with 

 the alkalies of the soil, and the soluble carbohydrate material. By 

 simply triturating the soil sample with pure water but a very 

 small percentage of the former class of compounds is ever ex- 

 tracted, while soluble carbohydrates are present in soils only in 

 exceedingly small quantities, except in rare cases. In these tests 

 dried, water solube humus and dextrose were used and two sets 

 of experiments were run, in one of which the solution to be 

 reduced contained .2 per cent of dried humus and the other of 

 which contained 1 per cent of dextrose. The addition of humus 

 produced a very dark brown solution, much darker in fact than 

 any solution that can be obtained by triturating, even soil high 

 in humus, with water. The analytical procedure was the same 

 as that above given and the results are expressed in Table IV, 

 and represent averages of closely agreeing duplicates. 



Effect of Dextrose 



