630 APPENDIX 



metallic mercury added and the contents of the flask digested until color- 

 less. Oxidation is completed by adding, while stjll boiling hot, powdered 

 potassium permanganate until the solution is green. It is then allowed 

 to cool and transferred with 250 cc. of nitrogen-free water to a copper 

 flask of about 700 cc. capacity and enough strong alkali solution l added 

 to more than neutralize the acid. The flask is then immediately con- 

 nected with a still, the ammonia distilled off and collected in a flask 

 containing a measured amount of standard hydrochloric acid. The ex- 

 cess of hydrochloric acid is then titrated back with standard ammonium 

 hydroxid, using lacmoid as indicator, and the amount of nitrogen in the 

 soil calculated. A convenient strength of ammonia solution is one in 

 which i cc. is equivalent to .0032 g. nitrogen. 



Duplicates should check within 0.2 cc. A blank determination must 

 be run, by using approximately .5 g. pure sugar instead of the soil sample, 

 and a correction made for the nitrogen in the reagents used. 



Phosphorus. For the phosphorus determination the soil is decom- 

 posed by heating with sodium peroxid as given on page 145, Bulletin 

 105, Bureau of Chemistry, U. S. Department of Agriculture. 



Five grams of ordinary soil are thoroughly mixed with 10 g. of sodium 

 peroxid in an iron crucible of about no cc. capacity, the flame applied 

 directly to the surface just long enough to start the action, the crucible 

 covered, and the heating continued over a low flame for twenty-five 

 minutes. The tip of the flame should just touch the bottom of the 

 crucible and the heat be kept low enough so the peroxid will not fuse. 

 In decomposing a soil very low in organic matter, such as some subsoils, 

 o.i to 0.5 g. of powdered sugar should be added to favor the reaction. 



Peat soils are usually high in phosphorus, and 2\ g. are sufficient for 

 the determination. Such soils, high in organic matter, will not fuse 

 slowly when heated with peroxid, but by moistening the sample with 5 cc. 

 of calcium acetate of sufficient strength to fix the phosphorus, the organic 

 matter can be safely burned off, and after cooling, enough sugar added to 

 effect decomposition with sodium peroxid in the usual way. 



A f ter decomposition, the sample is washed into a beaker, the coarser 

 particles broken up, then transferred to a 500 cc. flask acidified with 

 hydrochloric acid and boiled for five minutes. A little strong nitric acid 

 is added to insure complete oxidation of the iron to the ferric condition. 

 It is then allowed to cool and made up to volume. There should be no 

 undecomposed soil in the bottom of the flask. The silica is allowed to 



1 Containing 60 Ib. Greenbank's alkali and 800 g. potassium sulfid for each 30 

 litres of water. 



