Feb. II, 1918 Effect of Season and Crop Growth on Soil Extract 329 



extracts may be decolorized with carbon-black. Take up with 20 c. c. of hot distilled 

 water acidified with hydrochloric acid diluted i to i. Digest for a short time on the 

 steam bath to insure total solution. Filter and wash the dish and the fimnel with 

 hot water. Do not permit the total volume of solution to exceed 50 c. c. Make 

 faintly alkaline with ammonia, heat to boiling, add 5 c. c. of 10 per cent ammonium 

 chlorid and 5 c. c. of saturated ammonium oxalate. Cover solutions with watch 

 glasses, place on steam bath at moderate temperatiue (about 60° C), and allow to 

 stand overnight to insure complete precipitation. Filter on quantitative filter paper. 

 Wash till free from chlorids, using successive small portions of hot water. Dissolve 

 the precipitate in 50 c. c. of hot sulphuric acid diluted i to 4, receiving the acid and 

 hot water subsequently used for washing the filter paper in the beakers used for 

 precipitation. Titrate the hot solution with N 1I200 potassium permanganate, i c. c. 

 of which is equivalent to o.i mgm. of calcium. 



Potash. — Measure 200 c. c. of water extract into a 200-c. c. casserole, acidify with 

 0.5 c. c. of sulphuric acid diluted i to i, and evaporate to dryness on the steam bath. 

 Heat gently on an asbestos hot plate and keep the casserole constantly in motion to 

 prevent spattering imtil the excess of sulphuric acid has volatilized. Then ignite 

 over a Meeker burner until a white or gra^dsh white residue is obtained. Cool and 

 take up the residue in successive small portions of hot distilled water. Filter through 

 5.5 cm. quantitative filter paper, using 30 to 40 c. c. of water. Acidify with three or 

 four drops of hydrochloric acid diluted i to i. Add 8 to 12 drops of platinic-chlorid 

 solution and evaporate to a pasty consistency on the water bath ; care shoxild be exer- 

 cised to avoid overheating. Cool. Take up the residue in 5 c. c. of 95 per cent 

 alcohol, observe that an excess of platinic chlorid is present. Tritiu-ate the precipitate 

 carefully with a rubber "policeman" and filter at once on a carefully prepared and 

 weighed Gooch crucible. Wash with 95 per cent alcohol till the filtrate is colorless, 

 then with 30 to 40 c. c. of ammonium chlorid, 100 gm. to 500 c. c. of water, which 

 has been saturated with potassium platinic chlorid. Wash once with 80 per cent 

 alcohol and then thoroughly with 95 per cent alcohol. Dry in an oven at 100° C. 

 and weigh. Calculate the weight of potassium. 



With the use of the known solutions previously prepared and the 

 above methods, the following results (Table IV) are typical of the ac- 

 curacy obtained. 



27809°— 18 3 



