59 



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

 all the positive evidence it would seem that a very considerable 

 portion of the nitrogen in the soil exists in other forms than pro- 

 tein. For example. Potter and Snyder (1916) found an average of 

 20.46 per cent of the alkali soluble nitrogen of 'a soil to be non- 

 protein in nature. Bacteria and fungus spores all contain chitiri 

 which on hydrolysis yields glucosamine which will give amino 

 (-NH,) nitrogen of non-protein origin. 



The average C/N ratio that exists in this series of six mineral 

 soils studied has been shown by Gortner (1916 a) to be 12.23. The 

 average nitrogen content of the six soils is 0.355 per cent which 

 would indicate 2.22 per cent protein (NX6.25) if all of the nitrogen 

 existed in this form. However, the total organic matter in these 

 soils averaged 7.48 per cent (carbonX 1.724), showing that less 

 than 30 per cent of the soil organic matter could be of protein na- 

 ture. This is shown equally well by a comparison of the C/N 

 ratios. The average analyses of sixteen plant proteins as recorded 

 by Mathews (1915) gives carbon 52.08 per cent and nitrogen 17.73 

 per cent. The average C/N in these vegetable proteins is 2.94. 

 The high C/N ratio in soils indicates that the organic matter does 

 not consist essentially of protein material (cf. however, Gortner 

 1917, when a ratio of 3.06 was found indicating that the organic 

 matter in this instance was essentially protein). 



In view of the desirability of demonstrating the presence or 

 absence of proteins in soils an attempt was made to isolate from 

 a soil either alcohol soluble or salt soluble proteins. A 6 inch 

 bulk sample of Fargo silt loam from Morristown, Rice County, 

 containing 0.397 per cent of nitrogen in the air dry soil, was used. 



a. Extraction with 70 per cent ethyl alcohol. The soil was 

 first leached with 1 per cent hydrochloric acid to the absence of 

 calcium and washed with distilled water until practically all chlo- 

 rfdes were removed. For this purpose sixty-one 100 gram por- 

 tions were taken. It required about 150 liters of acid to remove 

 all traces of calcium. 



After leaching, the soil was allowed to air dry in the green- 

 house and there remained 5700 grams air dry soil. Five hundred 

 gram portions were placed in twelve 2.5 liter acid bottles and ex- 

 tracted successively with 70 per cent ethyl alcohol. A fresh por- 

 tion of alcohol was added to the first bottle of the series, shaken, 

 allowed to stand over night, syphoned off, and placed in the bottle 

 next ahead in the series. This was continued until six successive 

 portions of fresh alcohol had been added. The alcohol was ab- 

 sorbed by the dry soil to such an extent that a 500 gc. portion of 

 fresh alcohol had to be added to the bottles towards the end of 

 the series. Almost 15 liters of alcohol were used, but only a little 

 over 10 liters were regained at the end, since so much was retained 

 by the soil. 



The combined extracts were filtered until practically free of 

 clay and then concentrated under diminished pressure at a tem- 

 perature of 55 C. The extracts were in all cases straw colored. 



