26 METHODS OF ANALYSIS [Chap. 



24 Sodium Peroxid Method. — Official. 



Place 10 grams of sodium peroxid in an iron or porcelain crucible and thoroughly 

 mix with 5 grams of the soil as prepared under 2. If the soil has very little 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 the crucible until the re- 

 action is over and keep at a low red heat for 15 minutes. Do not allow fusion to 

 take place. By means of a large funnel and a stream of hot water, wash the charge 

 into a beaker, acidify with hydrochloric acid and boil. Transfer to a 500 cc. gradu- 

 ated flask, cool and fill to the mark. If the action has taken place properly there 

 should be no undecomposed soil in the bottom of the flask. Allow the silica to 

 settle and draw off 200 cc. of the clear solution. 



Precipitate the iron, aluminium, and phosphorus with ammonium hydroxid; 

 filter, wash several times with hot water, wash the precipitate back into the beaker 

 with a stream of hot water, and dissolve the precipitate in hot hydrochloric acid, 

 pouring the acid upon the filter to dissolve any precipitate adhering to it. Evapo- 

 rate the solution and washings to dryness on a water bath. Treat with dilute hy- 

 drochloric acid, heating if necessary, and remove the silica by filtration. Con- 

 centrate the filtrate and washings to about 10 cc, add 2 cc. of strong nitric acid, 

 and make alkaline with ammonium hydroxid. Add nitric acid very slowly and with 

 constant stirring until the solution is clear, avoiding an excess. Heat at 40°-50°C. 

 on a water bath, add 15 cc. of molybdate solution, [I, 7 (a) ], and maintain this tem- 

 perature for 1-2 hours. Let stand overnight, filter, and wash free from acid with 

 0.1% solution of ammonium nitrate, and, finally, once or twice with cold water. 

 Transfer the filter and precipitate to the same beaker and determine phosphorus 

 volumetrically as directed under 19. 



25 TOTAL POTASSroM.-OFFICIAL. 



Decompose the soil by the J. L. Smith method^ as follows: Triturate gently 

 0.5 or 1 gram of the finely ground soil with 1 gram of dry ammonium chlorid in a 

 smooth mortar, then add 8 parts of calcium carbonate and mix intimately. Trans- 

 fer the mixture to a platinum crucible, rinsing the mortar with a little calcium car- 

 bonate. Heat the crucible gradually until fumes of ammonium salts no longer 

 appear, and continue until the lower Ihree-fourths only of the crucible are brought 

 to a red heat. Maintain this temperature 40-60 minutes. The temperature should 

 be sufficient to keep the calcium chlorid formed by the reaction of ammonium chlo- 

 rid with calcium carbonate in a state of fusion. The mass, however, does not be- 

 come liquid since the fused calcium chlorid is absorbed by the large quantity of 

 calcium carbonate present. If the silicate "s fused by the application of too strong 

 heat, disintegration of the mass at the end of the operation with water cannot be 

 effected. Moreover, too high a temperature causes volatilization of alkali chlorids. 

 The mass contracts in volume during the ignition, and is usually easily detached 

 from the crucible. Transfer the fused mass to a porcelain dish, thoroughly slake 

 with hot water, and grind thoroughly with an agate pestle. After washing 5 times 

 by decantation with hot water, transfer to a filter and wash well, 300 cc. of wash 

 water being sufficient. To the filtrate add 10 cc. of concentrated hydrochloric 

 acid, and evaporate nearly to dryness in a porcelain dish. Treat with hot water 

 and 2 cc. of hydrochloric acid and filter by means of suction through a small filter 

 into a 150 cc. Jena beaker. Concentrate the solution to 30 cc, add 1.5 cc. of platinic 

 chlorid solution [I. 40 (b) ], evaporate to a sirupy consistency, and add 15 cc. of 

 2.25 N/1 acidulated alcohol (prepared by passing hydrochloric acid gas into a mix- 



