SOME RELATIONS OF ORGANIC MATTER IN SOILS 9 
from the i-millimeter sample and was passed through a sieve 
having 100 meshes to an inch. In this case it was necessary to 
grind the soil in order to pass all of it through the perforations. 
In the determinations of carbon the 100-mesh sample was 
used, while the determinations of nitrogen were made from the 
1-millimeter sample. The use of the finer soil in the determina- 
tion of carbon was based on the uncertainty of obtaining 
complete combustion with the coarser soil. 
The determinations were made in duplicate. All duplicates 
having a wider discrepancy than 0.02 per cent of carbon and 0.01 
per cent of nitrogen were discarded. 
Total organic carbon 
The total organic carbon was determined by the Parr Com- 
bustion Method, as described in Bulletin 107 (revised) of the 
United States Bureau of Chemistry, page 234. 
Total nitrogen 
The total nitrogen was determined by the Kjeldahl method. 
Ten grams of 1-millimeter soil was digested with 30 cubic centi- 
meters of sulfuric acid (specific gravity 1.84) and 0.4 gram of 
cupric sulfate, in 500-cubic-centimeter Kjeldahl Pyrex flasks 
at low heat for twenty minutes. Ten grams of potassium sul- 
fate was added and the digestion was continued for three hours. 
The residue was diluted to 350 cubic centimeters of water and 
transferred to an 800-cubic-centimeter Kjeldahl flask; from 80 
to 90 cubic centimeters of alkali solution was added and the 
ammonia was distilled into 1-10 N sulfuric acid. The distillate, 
measuring about 200 cubic centimeters, was titrated with 1-10 
N sodium hydroxide, two or three drops of methyl red solution 
being used as an indicator. 
SERIES I 
Soil treatment and cropping systems 
The plats in Series I were under experimentation for a 
period of ten years, from 1910 to 1919. A statement of the soil 
