62 F. B. GUTHRIE AND L. COHEN. 



Clay. Loam. Sand. 



Soluble in 1* citric acid {££ ;0115 ... ;«*... ;0055 



Soluble in distilled ( K 2 '0057 ... '0061 ... '0027 

 water \ P 2 5 '0027 ... '0026 ... '0019 



After the pots had stood a month, the soil in each pot 

 was well mixed and all lumps broken up, after which a 

 fair sample was taken without sifting, and dried at air 

 temperature. 



For the citric soluble determinations 100 grams of air- 

 dried soil were placed in a Winchester with a litre of one 

 per cent, solution of pure citric acid, the bottle being then 

 fixed in a mechanical shaking apparatus (end over end 

 motion) making approximately 50 revolutions per minute, 

 and shaken continuously for 20 hours. With this solvent 

 it has been shown by A. D. Hall that no further quantity 

 of phosphoric acid or potash goes into solution after that 

 time. The shaking being completed, the Winchester was 

 allowed to stand in an upright position for some hours, 

 after which the clear supernatant liquid was syphoned off 

 and filtered through a dry paper. 



Of the clear filtrate 500 cc. were taken and evaporated to 

 dryness with about 50 cc. of nitric acid. The residue was 

 then ignited gently at a low heat, and on cooling taken up 

 with hydrochloric acid, using the molybdate method for 

 PoOo, and the platinic chloride method for K 2 0. 



To obtain the water-soluble extract, 200 grams air-dried 

 soil were shaken in a Winchester with a litre of distilled 

 water for 20 hours in the above described apparatus. After 

 standing for about 6 hours, the clayey liquid was syphoned 

 off and filtered under pressure through a Pasteur filter 

 candle by means of a force pump. 500 cc. of the clear 

 filtrate were evaporated to dryness with a few drops of 

 HN0 3 , proceeding in the same manner as for citric soluble. 

 The results of the analyses are given as follows: — 



