SOILS. 



VI. Constituents insoluble in water, but soluble in 

 dilute hydrochloric acid. From 50 to 100 grms. of the 

 residue obtained in V. (previously washed, dried, 

 and uniformly mixed), are weighed off, mixed with 

 water, in a flask, to a thin paste, heatejd, and hydro- 

 chloric acid gradually added until the effervescence 

 ceases ; the mixture is then heated for some time, with 

 frequent agitation, the insoluble residue filtered off 

 and well washed. The solution is concentrated by 

 evaporation, weighed or measured, and divided into 

 separate portions for the different determinations. If 

 the soil contain much organic matter, it must be feebly 

 ignited with access of air previously to the extraction 

 with hydrochloric acid. 



a. Silicic acid. The solution is evaporated to dry- 

 ness with addition of some nitric acid. 



b. Sulphuric acid. From a weighed portion of the 

 acid solution, filtered from the silica, the sulphuric 

 acid is precipitated by chloride of barium. 



c. Alkalies. Another portion of this solution is 

 treated as in V.,/, with baryta- water. 



d. Phosphoric acid, lime, magnesia, alumina, protoxide 

 of manganese, and protoxide of iron, are separated and 

 determined in the greater portion of the solution 

 filtered from the silica ; according to the method given 

 in No. 26. 



e. The carbonic acid, may be determined in a separate 

 portion of the washed soil, as in alkalimetrical exa- 

 minations. 



/. A small quantity of copper and arsenic some- 

 times contained in the soil may be determined by a 

 special experiment. (See No. 26.) 



VII. Constituents insoluble in dilute hydrochloric acid. 

 A small quantity (about 5 or 10 grms.) of the 

 residue obtained in VI., is heated with several times its 

 weight of concentrated sulphuric acid, until the 

 greater part of the acid has been expelled. By this 



