226 Analysis of Soils. [Oct., 



Amount brought up, _ _ _ 98.8 



Substances not yet determined, - - 1.2 



100.0 



We shall describe the method of separating the alkalies after 

 completing the description of other parts of this analysis. 



Let us return to the examination of the insoluble silicates and 

 examine the nature of the bases which are united with the silicic 

 acid. The weight was 84 grains. In order to effect this analysis 

 we have to render the silicates soluble in acids. This is done by 

 melting them in a platina crucible, with thrice their weight of 

 pure carbonate of soda. Soluble alkaline silicates being produced 

 we have no difficulty in dissolving the whole in water and chlo- 

 rohydric acid. The solution is to be made entire, and is to be 

 rendered acid. Then it is to be evaporated to entire dryness, in 

 a porcelain capsule, and the heat is kept up so long as any vapor 

 and fumes are given off. Then allow the capsule to cool, and 

 moisten the whole of the dry mass with chlorohydric acid, and 

 dissolve the soluble matters in distilled water. By this process 

 the silicic acid is rendered insoluble, and the bases which were 

 united with it are readily soluble in acid. Collect the silica on 

 double filters as before described, wash so long as any acidity 

 remains; and then dry and burn the filters separately, and weigh 

 the silicic acid while it is still warm. The weight we will sup- 

 pose to be 78 grains; then 6 grains of the bases has been sepa- 

 rated and is in the solution Avhich we have filtered. This solu- 

 tion is to be treated with a little nitric acid, and boiled to per- 

 oxidize the oxide of iron, so that it may be precipitated entirely 

 by ammonia. Aqua ammonia is then added to the solution in 

 excess beyond saturation, and all the alumina and per-oxide of 

 iron will be separated in the form of a gelatinous precipitate. 

 This is to be collected on a filter, and must be washed with boil- 

 ino- water for some time. Then the precipitate may be removed 

 from the filter with a silver or platina spatula, and is to be placed 

 in a large silver crucible and boiled with an excess of pure pot- 

 ash (potass a I'alcohol) until all the alumina is dissolved by the 



