154 CHEMISTRY OF FARM PRACTICE 



tilled water or rain water. At the end of an hour examine the paper 

 by looking at the bottom of the tumbler. If both papers are red, 

 the soil is acid; if both are blue, it is alkaline, and, if unchanged, the 

 soil is neutral. 



(c) Phosphorus. The following provisional method for determining 

 the phosphorus present is given together with some explanation on 

 page 234, Bulletin 107 (revised) Bureau of Chemistry. Weigh 10 

 grams of sodium peroxide into an iron or porcelain crucible and thor- 

 oughly mix with it 5 grams of the soil. If the soil is very low in organic 

 matter, add a little starch to hasten the oxidation 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. Quickly cover the crucible until the reaction is over 

 and keep at a low red heat for fifteen minutes. Do not allow fusion 

 to take place. By means of a large funnel and a stream of hot water, 

 transfer the charge now free from organic matter to a 500 cubic centi- 

 meter graduated flask. Acidify with hydrochloric acid and boil. Let 

 cool and make up to the mark with distilled water. If the action has 

 taken place properly, there should be no particles of undecomposed 

 or colored soil in the bottom of the flask. Allow the silica to settle 

 and draw off 200 cubic centimeters of the clear solution. 



Precipitate the iron, alumina, and phosphorus with ammonium 

 hydroxide added in slight excess to the warm solution, heat, stir, 

 filter and wash several times with hot water, discarding the filtrate. 

 Return the precipitate to the beaker with a stream of hot water, hold- 

 ing the inverted funnel over the beaker, retaining the filter paper in 

 the funnel, and dissolve the precipitate in hot hydrochloric acid, pour- 

 ing acid upon the filter to dissolve any precipitate remaining and add 

 this acid washing to the dissolved precipitate. Evaporate the solu- 

 tion and washings to complete dryness on a water bath to dehydrate 

 the silica. Take up with dilute hydrochloric acid, heating if necessary, 

 and filter out the silica. Evaporate the filtrate and washings to about 

 10 cubic centimeters, add 2 cubic centimeters of concentrated nitric 

 acid, and just neutralize with ammonium hydroxide. Clear up with 

 nitric acid, avoiding an excess. Heat at 40 to 50 on a water bath, 

 add 15 cubic centimeters of molybdic solution, keeping at this temper- 

 ature for from one to two hours. The molybdic solution is made as 

 follows: Dissolve 100 grams of molybdic acid in 417 cubic centimeters 

 of ammonia sp. gr. .96 and pour the solution slowly into 1250 cubic 

 centimeters of nitric acid sp. gr. 1.20, keep the mixture in warm place 

 for several days or until a portion heated to 40 C. deposits no yellow 

 precipitate. Decant the solution for any sediment. Let stand 

 over night, filter, and wash free of acid with a ^ per cent solution of 



