106 AGRICULTURAL CHEMISTRY 



capable of being acted upon by decaying animal and 

 vegetable matter and undergoing chemical changes which 

 prepare them for plant food. Since silicon forms the 

 principal acid element which enters into the composition 

 of rocks, soils, building stones, glass, brick, and porcelain, 

 and is associated with the elements in the soil which serve 

 as plant food, it follows that it is an important element in 

 industrial operations and in agriculture. 



Experiment 23. To about 5 cc. of sodium silicate in a test-tube 

 add a few drops of HC1 and observe the result. Then add NaOH 

 and observe the result. Add more HC1, and evaporate the ma- 

 terial to dryness in the evaporating dish. When cool, test the 

 solubility of the residue in water. 



Questions, (i) What was formed when HC1 was added to 

 sodium silicate ? Write the reaction . ( 2 ) What was the appearance 

 of the above product? (3) What effect did the NaOH have, and 

 what was formed ? (4) What was formed when the material was 

 evaporated to dryness? (5) What can you say as to the solubility 

 of the product ? 



Problem /.What per cent, of SiO 2 in clay, Al 4 (SiO 4 ) 3 .H 2 O? 



Problem 2. How much silicic acid is formed when 10 grams of 

 HC1 act upon K 4 SiO 4 ? 



