62 Journal oj Agricultural Research voi. vi, no. 2 



the Avriters that this would hold for the material precipitated by acid 

 from the alkali extract, but perhaps this would not be true of the organic 

 nitrogen compounds remaining in solution. It has been pointed out by 

 Shorey (7) that many organic compounds have been isolated from the 

 alkali extract of soil, which, though relatively quite soluble in water, can 

 not be detected in or isolated from the water extract of soils. Therefore 

 it has seemed that information might be obtained relative to the degree 

 of decomposition of the organic matter in the soil by determining the 

 proportion of nitrogenous compounds left in solution after the precipita- 

 tion of the proteins by a suitable reagent v/as completed. It was with 

 these problems in mind that the preliminary investigation was carried out. 



EXPERIMENTAL METHOD 



The general procedure followed was to determine the nitrogen in the 

 alkali extract of soil with and without added material and the determina- 

 tion of nitrogen in the filtrate from the precipitate of the proteins in the 

 alkali extract of soil with and without added material. The recent crit- 

 ical examination of a few protein precipitants by Greenwald (3) led us to 

 use trichloracetic acid as our precipitant. 



The detailed procedure was as follows: Soil, ground to pass a sieve of 

 100 meshes to the inch, was extracted with i per cent of hydrochloric acid 

 until no calcium was found in the wash water. After air drying, 100 

 gm. were placed in an 800 c. c. bottle and 500 c. c. of a 1.5 per cent solu- 

 tion of sodium hydroxid added. After shaking the mixture for 2 hours 

 it was centrifuged for 5 minutes in a bowl centrifuge having a speed of 

 18,000 revolutions per minute. Two 25 c. c. portions of the clear but 

 deeply colored extract were analyzed for total nitrogen by the Gunning- 

 Arnold method. Two 25 c. c. portions were neutralized with sulphuric 

 acid, sufficient trichloracetic acid in solution added to give a 2.5 per 

 cent solution of the acid and a total volume of exactly 30 c. c. After 

 centrifuging, 10 c. c. portions were taken from each tube and analyzed 

 for nitrogen by the Bock and Benedict (i) modification of the Folin and 

 Denis method (2). This was called the soluble nonprotein nitrogen. 



The same procedure was used where material was added to the soil. 

 In the case of guanin, hypoxanthin, and glucosamin,* weighed portions 

 of the compounds were added to the soil, which was then shaken with 

 the alkali. The hydrolyzed casein was prepared as directed by Green- 

 wald (3), which consisted, in brief, of boiling the casein for 40 hours with 

 hydrochloric acid, the removal of the acid under diminished pressure, 

 neutralization with sodium hydroxid (NaOH), and filtration. After 

 mixing the filtrate with animal charcoal it was again filtered and final 

 filtration carried out after crystallization of the tyrosin. For all the 

 remaining materials solutions were prepared, sometimes with the aid of 

 a little Nlio acid or Njio alkali. vSuitable amounts of the solutions were 



* We wish to express our thanks to Prof. P. A. Kober for the samples of the hypoxanthin and guanin, 

 «nd to Dr. A. W. Dox for the sample of glucosamin. 



