ON THE EXAMINATION OF SOILS 143 



solution to a proportionately larger volume. 

 In very sandy soils, where the proportion of in- 

 soluble matter is 90 per cent or more, 20 gms. 

 of soil are to be digested with 100 cubic centi- 

 meters of acid and the solution made up to 500 

 cc.; or a larger quantity may be used, preserving 

 the same proportions. It is very important that 

 the analyst assure himself of the purity of all 

 the reagents to be used in the analysis of soils 

 before beginning the work. 



In a flask of 200 cc. capacity place 10 gms. 

 of air-dried soil and 100 cc. of hydrochloric acid. 

 Close flask with cork, carrying a glass tube 

 about 2 ft. in length to act as reflux condenser. 

 Place flask in water-bath and keep at boiling 

 temperature for ten hours with occasional shak- 

 ing. Transfer contents of flask to a beaker, and 

 bring residue on to filter and wash with distilled 

 water; dry residue and weigh as insoluble ma- 

 terial. Make solutions and washings up to 500 

 cc. with distilled water. 



Iron and Alumina. 100 cc. of above solution 

 are made slightly alkaline with ammonia, then 

 boiled to expel excess of ammonia, filtered, 

 and well washed with hot distilled water. The 

 precipitate is iron, alumina and phosphates. 

 After drjdng, igniting in tared crucible, and 

 weighing the desiccated product, the iron and 

 alumina may be separated as follows: Bring 

 residue of iron and alumina into a beaker, add 15 

 cc. of dilute sulphuric acid (1 of acid and 4 of 



