61 



soil. The alcohol syphoning back became colorless several hours 

 before the extraction was stopped. At the end of the extraction 

 the solution in the flask was deep straw color. 



The total alcohol extract was evaporated to small volume and 

 then the total nitrogen determined, which was found to be 0.0011 

 gram. This .was equivalent to 0.0660 gram of nitrogen in 6 kilo 

 of soil before leaching with acid. It will be recalled that 0.1320 

 gram nitrogen dissolved in the 70 per cent alcohol after first leach- 

 ing with 1 per cent hydrochloric acid. 



This would indicate that many of the organic nitrogenous 

 compounds are in combination with the lime or other bases present 

 in the soil, and that this combination is broken up when leached 

 with 1 per cent hydrochloric acid. 



c. Extraction with 10 per cent sodium chloride. After com- 

 pletion of the alcoholic extraction, the soil residue was dried in an 

 air o.ven at about 65 C. and placed in a 20 liter bottle. To this 

 was added 2000 cc. of 10 per cent sodium chloride solution for 

 each kilo of dry soil. The bottle was shaken repeatedly and allowed 

 to settle over night. The presence of an electrolyte caused the 

 clay to settle rapidly, so that a clear solution could be withdrawn. 

 After the soil had been in contact with the salt solution 20 hours, 

 two 100 cc. portions were withdrawn and analyzed for nitrogen. 

 The results showed that 0.1350 gram nitrogen was contained in .5 

 liters of the supernatant liquid. After shaking and standing for 

 three days duplicate determinations were again made on 100 cc 

 portions with the result that 0.1600 gram nitrogen was present in 

 the corresponding solution. This indicates that the longer the soil 

 is in contact with the sodium chloride solution the greater the 

 amount of organic nitrogen extracted. 



Two 500 cc. portions of the salt extract were used for precipi- 

 tation with phosphotungstic acid. After the addition of 45 cc. of 

 concentrated hydrochloric acid, the phosphotungstic acid was 

 added. The gelatinous precipitates formed were filtered on an 

 ordinary funnel and washed with the filtrate, and then used for 

 the determination of nitrogen by the usual method. The duplicates 

 averaged 0.0028 gram nitrogen, thus making the total nitrogen 

 precipitated by phosphotungstic acid 0.0280 gram in the 5 liters of 

 supernatant liquid. This shows that 17.50 per cent of the nitrogen 

 extracted from the residual soil was precipitated by phosphotung- 

 stic acid. This represented the maximum protein nitrogen in the 

 10 per cent sodium chloride solution. 



