41 



2. Calcareous black grass-peat. Duplicate samples of 15 

 grams were hydrolyzed for 48 hours in the presence of 100 cc. con- 

 stant boiling hydrochloric acid, and the analysis conducted as de- 

 scribed under the method for a peat soil. 



In the precipitation of the phosphotungstic acid with barium 

 chloride, it was difficult to determine when the precipitation was 

 complete. On addition of barium chloride a precipitate formed and 

 the pink color slowly disappeared. Both sodium hydroxide and 

 barium chloride were repeatedly added. The change in color oc- 

 curred several times during a half-hour. At all times test portions 

 gave immediate granular precipitates with both sodium sulfate 

 and barium chloride. This indicated that we could not depend 

 upon the test with sodium sulfate to determine when all the 

 phosphotungstic acid was precipitated. After the addition of a 

 large amount of barium chloride the solution was allowed to stand 

 several hours in order to allow equilibrium to be established. At 

 the end of this time test portions gave a heavy precipitate with 

 sodium sulfate, but no action with barium chloride. In all subse- 

 quent work, both with peat and mineral soils, the addition of barium 

 chloride to the solution of the phosphotungstates was extended 

 over an hour or more and the precipitate then allowecl to settle 

 over night. 



This barium phosphotungstate precipitate was washed thor- 

 oughly by decantation with hot water until free of chlorides. This 

 operation was carried out in the original beaker, and in the case of 

 many mineral soils required from 500 to 1000 cc. to remove all 

 chlorides. The washed precipitate of barium phosphotungstate and 

 filter on kjeldahling gave 0.0021 gram nitrogen retained by Sample 

 I and 0.0055 gram by Sample II. 



The experimental data showing the grams of nitrogen and 

 per cent of tgtal nitrogen are given in Table V. 



Table V . Nitrogen distribution in calcareous black grass-peat. 



Grams nitrogen | Per cent of total nitrogen 



