PRACTICE XXXI 



SOIL ANALYSIS ; DETERMINATION OF THE PLANT FOOD 

 SOLUBLE IN STRONG HYDROCHLORIC ACID* 



Place 10 g. of the air-dried soil in a 200-cc. Erlenmeyer flask, add 

 100 cc. of hydrochloric acid (sp. gr. 1.115), close with a rubber stop- 

 per in which is a glass tube 18 inches long, and digest for ten hours 

 on a water bath, at the temperature of boiling water, shaking once 

 every hour. Dilute, filter through a 15-cm. filter, wash free of chlo- 

 rids with hot water, and evaporate filtrate and washings to complete 

 dryness after adding 5 cc. of nitric acid to destroy organic matter. 

 Take up with about 10 cc. hydrochloric acid and about 25 cc. of 

 water, heat thirty minutes, filter, and wash with hot water. Cool, 

 make filtrate and washings up to exactly 500 cc., mix thoroughly, 

 and put in dry stoppered bottle. Label it Solution A. 



1. Phosphorus. 



Precipitate phosphorus, iron, and aluminum in 200 cc. of Solution A 

 with ammonium hydroxid, filter, dissolve precipitate in nitric acid, 

 and determine phosphorus in the solution as directed in Practice 

 XX, omitting running to dryness to remove silica. 



cc. HXO 3 cc. KOH to mg. P % P P in 



used dissolve 2 million 



ppt. of soil 



Av 



1 This is the official method of the Association of Official Agricultural Chemists, 

 and is similar to the methods used in other countries. 



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