i8 



Morris J. Blish 



Tables No. XI and XII show the humus nitrogen, the per 

 cent of nitrogen in humus and humus-nitrogen ratio of all of the 

 composites of the transition series, using the figures for only 

 gravimetric humus determinations. 



Table XII. 



Humus-Nitrogen Ratio for Composite Samples from 

 Different Areas 



As previously indicated, considerable work was done on the 

 estimation of humus in the soils of the transition series by dif- 

 ferent colorimetric methods. Solutions or extracts of humus in 

 4 per cent ammonia were prepared by the usual method from 

 each individual field soil, making 180 solutions in all. These 

 solutions, of course, varied in depth of color from deep black to 

 almost colorless solutions. They were compared, first with the 

 eye alone, and later the humus content in each was estimated, 

 using a standard and a colorimeter. Colorimetric comparisons 

 were also made using merely the soil itself, both in a moist and 

 a dry condition. Twenty-five gram samples were weighed out in 

 small porcelain dishes, and attempts were made to arrange them 

 according to amount of humus, this being estimated by the depth 

 of color in the soil. The results of the latter were fairly satis- 

 factory when the soils were from the same locality, but when 

 soils of different localities were brought together, the extreme dif- 

 ferences in types of color, caused by substances other than humus, 

 such as lime and iron, made a satisfactory and reliable comparison 

 by this method impossible. This is shown by the following 

 tables. From them it is seen that when soils of the same area 

 were taken, they were arranged fairly accurately according to 

 depth of color, but when all were mixed together, the uniformity 



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