226 SOILS. 



tracted with water, the filtered solution evaporated to 

 a small bulk, and the reactions made, given under 

 nitric acid, No. 116. 



V. The constituents soluble in water. A large quan- 

 tity of the air-dried soil, from 1000 to 2000 grammes, is 

 heated nearly to ebullition, with water, for a consider- 

 able time; the residue is filtered off and thoroughly 

 washed with hot water. The whole liquid is evaporated 

 to about its original volume, carefully weighed or 

 measured, and separate portions of it, weighed or 

 measured off, are employed for the determination of 

 the following constituents. 



a. The total weight of the portion soluble in water 

 is ascertained by evaporation to dry ness. 



b. Sulphuric acid is precipitated by chloride of 

 barium from the solution acidified with hydrochloric 

 acid. 



c. Chlorine is precipitated by nitrate of silver, after 

 acidification with nitric acid. 



d. Silicic acid. The solution is mixed with hydro- 

 chloric acid, evaporated to dryness, the residue ex- 

 tracted with dilute hydrochloric acid, and the silica 

 filtered off. 



e. Lime, magnesia, alumina, protoxide of iron, andprot- 

 oxide of manganese may be contained in the filtrate from 

 d; they may be separated as in No. 81. 



/. Potassa and soda. The solution is mixed with 

 hydrochloric acid, evaporated to dryness, the residue 

 dissolved in a little water, baryta- water added in excess, 

 the mixture digested for some time, filtered off, and 

 the baryta and lime precipitated from the filtrate by 

 carbonate of ammonia. The solution filtered from 

 these can contain only potassa and soda, which are es- 

 timated as chlorides, and are separated as usual. 



g. Phosphoric acid, which can only be present if the 

 solution contain no lime, &c., is precipitated as phos- 

 phate of magnesia-ammonia. 



