II. METHODS FOR THE ANALYSIS OF SOILS. 



Total Organic Carbon. Optional Official. 



[Page 14, paragraph 4.] 



Thoroughly mix 2 grams of soil (1 gram of soils high in organic matter), 0.75 gram of 

 magnesium powder, and 10 grams of sodium peroxid, in a closed dry calorimeter 

 bomb, by shaking the bomb back and forth. Explode the charge by means of elec- 

 tricity or by dropping a red-hot plug into the bomb through a valve which closes 

 automatically as soon as the plug enters. Remove the fused charge from the bomb, 

 using as small an amount of hot distilled water as possible, bring to a boil, and transfer 

 to a receiving funnel of a Parr's apparatus for total carbon. a 



From the acid funnel run 50 cc of sulphuric acid (1 part concentrated acid to 2 

 parts water) into a 150 cc Erlenmeyer flask. Connect the apparatus and slowly turn 

 in the contents from the receiving funnel. The carbon dioxid generated passes 

 through a capillary tube into a graduated burette. 



Bring the contents of the flask to a boil, then fill the flask with distilled water from 

 the receiving funnel so as to push the gases into the graduated burette. Note the 

 temperature and pressure and the reading on the burette. Absorb the carbon dioxid 

 by passing the gas into an ordinary absorption pipette which contains a 30 per cent 

 potassium hydroxid solution. When a constant reading has been reached note the 

 difference between it and the first reading, which gives the number of cubic centi- 

 meters of carbon dioxid equivalent to the carbon in sample. 



Determine by the usual method the carbon dioxid in the soil as carbonates, using 

 10 grams of soil, and subtract the inorganic carbon from the total to find the organic 

 carbon. 



TOTAL PHOSPHORUS. 

 [Page 16, paragraph (f).] 



(3) SODIUM PEROXID FUSION METHOD. PROVISIONAL. 



Weigh 10 grams of sodium peroxid into an iron or porcelain crucible and thoroughly 

 mix with it 5 grams of the soil. If the soil is very low in organic matter, add a little 

 starch to hasten the action. Heat the mixture carefully by applying the flame of a 

 Bunsen burner directly upon the surface of the charge and the sides of the crucible 

 until the action starts. Cover crucible until reaction is over and keep at a low red 

 heat for fifteen minutes. Do not allow fusion to take place. By means of a largo fun- 

 nel and a stream of hot water, transfer the charge to a 500 cc measuring flask. Acidify 

 with hydrochloric acid and boil. Let cool an<l nuikr up to the mark. If the action 

 has taken place properly there should be no particles of undecomposed soil in the 

 bottom of the flask. Allow the silica to settle and draw off 200 cc of the clear solut ion. 



Precipitate the iron, alumina, and phosphorus with ammonium hydroxid; filter, 

 wash several times with hot water, return the precipitate to the beaker with a stream 

 of hot water, holding the funnel over the beakor, and dissolve the precipitate in hot 

 hydrochloric acid, pouring the acid upon the filter to dissolve any precipitate remain- 



a J. Amer. Chem. Soc., 1904, 26: 294, 1640. 



