5. Fargo clay loam 43 



6. Fargo silt loam 44 



7. Carrington silt loam 45 



8. Hempstead silt loam 45 



9. Prairie-covered loess 46 



10. Forest-covered loess 47 



11. Sphagnum-covered peat hydrolyzed in the pres- 



ence of nine times its weight of a mineral 

 subsoil 47 



12. Sphagnum-covered peat hydrolyzed in the pres- 



ence of metallic tin 49 



13. Analysis of a 1 per cent, hydrochloric acid extract 



of sphagnum-covered peat and (in part) of 

 calcareous black grass-peat 50 



14. Analysis of a portion of sphagnum-covered peat 



soluble in 4 per cent, sodium hydroxide and 

 precipitated by hydrochloric acid and (in 

 part) of a similar solution from a calcareous 

 black grass-peat 52 



15. Analysis of a portion of sphagnum-covered peat 



soluble in 4 per cent sodium hydroxide and 

 not precipitated by hydrochloric acid and (in 

 part) of a similar solution from a calcareous 

 black grass-peat 54 



16. "Jodidi numbers" ! 55 



17. Summary tables 57 



18. An attempt to isolate pure proteins from a soil 59 



a. Extraction with 70 per cent ethyl alcohol 59 



b. Extraction with absolute alcohol 6U 



c. Extraction with 10 per cent sodium chlor- 



ide 61 



III. Discussion 62 



A. Changes in nitrogen distribution in a protein when hy- 

 drolyzed in the presence of a mineral soil 62 



B. The human nitrogen, its origin, and significance 63 



C. The effect of the quantity of acid used for the hydrolysis 

 on the amount of nitrogen dissolved and the nitrogen 

 distribution in soils 66 



D. The percentage of soil nitrogen extracted by acid hy- 

 drolysis 66 



E. "Jodidi numbers" 67 



F. Attempts to extract proteins from the soil 67 



G. A consideration of the nitrogen distribution in different 

 extracts from the sphagnum-covered peat 67 



H. General conclusions in regard to the distribution of soil 



nitrogen in different soil types 68 



IV. Summary 70 



V. Literature cited 72 



Biographical 80 



