SOILS. 1 7 



(g) SULPHURIC ACID. OFFICIAL. 



Evaporate 100 or 200 cc of Solution A nearly to dryness on a water bath to 

 expel the excess of acid; then add 50 cc of distilled water; heat to boiling ami 

 Mid drop by drop a 10 per cent barium chlorid solution until no further precipi- 

 tation occurs. Continue the boiling for about 5 minutes ; allow to stand for 5 

 hours or longer in a warm place, pour the liquid on a tared gooch or on an 

 ashloss filter, treat the precipitate with from 15 to 20 cc of boiling water, trans- 

 fer to the filter and wash with boiling water until the nitrate is free from 

 chlorids. Dry the filter, ignite over a Bunsen burner, and weigh as barium 

 sulphate, which multiplied by 0.34293 gives the sulphur trioxid. 



(h) POTASSIUM AND SODIUM. 



(1) OFFICIAL METHOD. 



Treat the filtrate from the sulphuric acid determination (g) with ammonium 

 hydroxid exactly as in 5 (I), page 15. Evaporate the filtrate and washings to 

 dryness, heat below redness until ammonium salts are expelled, dissolve in 

 hot water, add 5 cc of barium hydroxid solution, and heat to boiling ; let 

 settle for a few minutes, and test a little of the clear liquid with more 

 barium hydroxid solution to be sure that enough has been added. When 

 no further precipitate is produced, filter and wash thoroughly with hot water. 

 Heat the filtrate to boiling, add ammonium hydroxid and ammonium carbonate 

 to complete precipitation of the barium, calcium, etc., let stand a short time on 

 the water bath, filter, and wash the precipitate thoroughly with hot water; 

 evaporate filtrate and washings to complete drjness, expel ammonium salts 

 by heat below redness, take up with a little hot water, add a few drops of 

 ammonium hydroxid, a drop or two of ammonium carbonate, and a few drops 

 of ammonium oxalate ; let stand a few minutes on the water bath, set aside for 

 a few hours, filter, evaporate to complete dryness on the water bath, and heat to 

 dull redness until all ammonium salts are expelled and the residue is nearly 

 or quite white. Dissolve in a minimum amount of water, filter into a tared 

 platinum dish, add a few drops of hydrochloric acid, evaporate to dryness on 

 the water bath, heat to dull redness, cool in a desiccator, and weigh as potas- 

 sium and sodium chlorids. Repeat heating until constant weight is obtained. 

 Dissolve in a small amount of water; if any residue remains, the separation 

 must be repeated until the residue of potassium and sodium chlorids is entirely 

 soluble. Dissolve the residue with water, add an excess of platinum chlorid, 

 and proceed as directed under "I. Fertilizers," (3) (a), page 11. 



Or, instead of the foregoing, evaporate to dryness a fresh aliquot of solu- 

 tion A, redissolve in water, treat directly with barium hydroxid, and from this 

 point proceed as above directed. 



(2) PROVISIONAL METHOD. 



Proceed as in the official method (1) through " let stand a short time on the 

 1 water bath " and complete as follows : 



Filter into a beaker, add a drop or two of hydrochloric acid and 1 cc of am- 

 monium sulphate (75 grams to 1 liter), digest several hours on water bath, and 

 filter into a tared platinum dish. Evaporate to complete dryness, heat to full 

 redness, add 1 gram of powdered ammonium carbonate, expel by heating, cool, 

 and weigh the sulphates of sodium and potassium. Determine potassium in the 

 usual manner. 



