34 



The general method employed in this investigation will be dis- 

 cussed in detail for two soils, a peat and a mineral soil, inasmuch as 

 the experimental conditions vary in minor details with the two 

 types. 



1. The method in detail for a peat soil. Duplicate samples 

 of 15 grams were hydrolyzed in the presence of hydrochloric acid 

 for 48 hours. The content of calcium oxide was taken into, account, 

 and corrections made so that the 100 cc. of hydrochloric acid used 

 was of sufficient concentration to neutralize the lime and at the 

 same time furnish a constant boiling acid. The hydrolysis was 

 carried out in 200 cc. long neck, round bottom Kjeldahl flasks, fitted 

 with modified Hopkins condensers made from a test tube which 

 fit rather loosely into the neck of the flask. By means of this device 

 any error due to products extracted from cork or rubber stoppers 

 was obviated. The flasks were heated to gentle boiling on the 

 same sand bath over an Argand burner, so that the rate of hydro- 

 lysis would be as near the same as possible. 



After completion of the 48 hour hydrolysis the mixture was 

 evaporated in a Claissen distilling flask under diminished pressure 

 until all the hydrochloric acid possible was driven off. The residue 

 after this distillation was dissolved in 100-150 cc. of water, 100 cc. 

 of 95 per cent alcohol, and an excess of calcium hydroxide sus- 

 pended in water was added and the ammonia distilled off into 

 standard acid at a temperature of 40-50 C. under a pressure of less 

 than 30 mm., distillation being continued for at least a half hour. 

 The results are listed under "ammonia nitrogen." 



The alkaline mixture in the distilling flask was filtered and 

 the precipitate well washed with hot water until free of chlorides. 

 A Kjeldahl determination was made of the filter and its contents, 

 and the results listed under "humin nitrogen." 



The filtrate and washings from the humin were acidified with 

 hydrochloric acid and concentrated under diminished pressure to 

 less than 200 cc. To this solution was added 18 cc. of concen- 

 trated hydrochloric acid and the whole heated on the water bath 

 until hot. A solution containing 15 grams of phosphotungstic acid 

 was then added and the heating on the water bath continued for 

 an hour. The flask was then set aside in a cool place for 48 hours. 

 The precipitate of the bases was then filtered off and washed as 

 directed by Van Slyke (1911). 



The basic phosphotungstates were suspended in 800 cc. of 

 water and brought into solution by the cautious addition of a 50 

 per cent solution of sodium hydroxide, a few drops of phenolph- 

 thalein being added to guard against too great an excess of alkali. 

 The phophotungstic acid was precipitated by the addition of a 

 slight excess of 20 per cent barium chloride, and the barium phos- 

 photungstate was filtered off and washed free of chlorides with 

 hot water. 



The filtrate and washings were united, acidified with hydro- 

 chloric acid, and concentrated under diminished pressure to a very 

 small volume. After cooling the residue was filtered, washed and 

 made up to 50 cc. volume. 



