II] SOILS 27 



ture of 2000 cc. of 95% alcohol and 152 cc. of hydrochloric acid, sp. gr. 1.20). Fil- 

 ter by means of suction through a small filter, wash with 80% alcohol, then with 

 ammonium chlorid solution [I, 40 (a) ], and finally with 80% alcohol. Dry the 

 precipitate on the filter and wash the precipitate with hot water into a weighed 

 platinum dish, using suction. Evaporate to dryness, heat in a drying oven for 

 an hour at 120°C., cool in a desiccator, weigh and calculate to potassium oxid (KjO). 



TOTAL ALKALIES. 



26 /. Lawrence Smith Method.* — Official. 



(1) Proceed as directed under 25 to the point indicated by the phrase "300 cc. of 

 wash water being sufficient" (the point at which the ignited mass has been 

 disintegrated and thoroughly washed with water). The filtrate contains the sili- 

 cate alkalies in the form of chlorids together with calcium chlorid and hydroxid. 

 Precipitate the calcium at once with ammonium carbonate solution; allow to settle, 

 decant the supernatant liquid into a porcelain (or platinum) dish, concentrate and 

 finally transfer the precipitate to the dish. When the volume is reduced to about 

 30 cc, add a little ammonium carbonate solution and ammonium hydroxid, heat 

 and filter into a porcelain (or platinum) dish, evaporate the filtrate to dryness on 

 a water bath and expel ammonium salts by ignition. Dissolve the residual alkali 

 chlorids in 3-5 cc. of water; a little black or dark brown flocculent matter usually 

 remains undissolved, while the solution may also contain traces of calcium. Add 

 2-3 drops of ammonium carbonate and ammonium hydroxid, warm gently, and fil- 

 ter through a very small filter into a weighed platinum vessel. Evaporate to dry- 

 ness on a water bath, heat the alkali chlorids to incipient fusion, cool, and weigh 

 as sodium and potassium chlorids; or, 



(2) Determine, by the above method, the quantity of alkalies in the insoluble 

 residue, 12, and add that obtained under 21 or 22. 



27 PHOSPHORUS SOLUBLE IN N/5 NITRIC ACID.— TENTATIVE. 



Digest 10 grams of air-dried soil in a stoppered flask, with 100 cc. of N/5 nitric 

 acid, for exactly 5 hours in a water bath kept at a temperature of 40°C. Filter the 

 solution through a dry paper, cool to room temperature, and titrate 20 cc. of the 

 filtrate with standard potassium hydroxid solution (carbonate-free), using phenol- 

 phthalein as indicator. From the data thus secured calculate the number of cc. 

 of N/1 acid and of water to make exactly 1 or 2 liters of acid of N/5 strength after 

 allowing for the quantity neutralized by the amount of soil to be used in the fol- 

 lowing procedure: 



Place 200 grams of the air-dried soil in a large, dry, glass-stoppered bottle and 

 add exactly 2000 cc. of N/5 nitric acid corrected for neutralization as above de- 

 scribed. With soils rich in available phosphoric acid, 100 grams of soil and 1000 cc. 

 of acid will be sufficient. Digest in a large water bath at a temperature of 40°C. 

 for exactly 5 hours, shaking thoroughly each half hour. At the end of the digestion 

 shake the contents of the bottle well and pour quickly upon a large, dry, ribbed fil- 

 ter of 2 thicknesses of paper and of sufficient size to receive the entire contents of 

 the bottle. Collect the filtrate in a dry vessel, pouring back on the filter until the 

 filtrate becomes clear. Evaporate 1000 or 500 cc. of the filtrate, according to the 

 quantity of soil used, to dryness in a porcelain dish; add a few cc. of nitric acid to 

 oxidize organic matter, etc., moisten the residue with hydrochloric acid, digest 

 with water, and filter into a 500 cc. flask. Add a solution containing 15 grams of 

 ammonium nitrate; then strong ammonium hydroxid until a permanent precipitate 

 forms, and then concentrated nitric acid slowly until the precipitate dissolves. 



