128 CHEMISTR V FOR A GRICUL TURAL STUDENTS 



151. In what proportions does silica exist in its compounds with bases? 



Compare phosphoric anhydride with silica in this respect. 



152. How may silicate of aluminium (clay) be artificially produced? 



What is the distinctive character of the precipitate obtained, and 

 what is the effect (i) of lime upon it, and (2) of heating it ? 



153. What silicates are fusible and what infusible? How may the 



properties of the silicates in this respect be utilised in pottery 

 making? From what are bricks made, and how does the 

 material used differ from that required for tile-making ? 



154. Of what is glass composed ? What silicates render glass " soft" or 



fusible, and what silicates render it "hard" or infusible? To 

 what is the green colour of bottle glass due ? 



155. Of what does soil consist, and how may the proportions of gravel, 



sand, and clay be determined ? 



156. Upon what does the wetness of a soil depend? State what is 



meant by the "capillarity" of a soil. By what means may the 

 porosity of a heavy soil be increased ? 

 *I57. Examine the tap water for dissolved silicates. 



Carbon : Marsh Gas. 



158. How are animal and vegetable charcoal prepared, and of what do 



they consist? Describe the process of " charcoal burning." 



159. Name the three allotropic modifications of carbon. Name three 



other elements already studied which exist in allotropic forms. 

 Which modification of carbon exists in lamp-black, coke, and 

 gas carbon, and how is each of these substances produced ? 



160. Upon what does the use of " bone-black " as a decoloriser depend ? 



What is the purpose of the block of animal charcoal used in a 

 charcoal filter? 



161. Explain the power possessed by wood charcoal of absorbing gases. 



Describe experiments which show its porosity and absorptive 

 power. How does this explain the use of charcoal as a deodoriser 

 and disinfectant? What relation exists between the condensibility 

 of gases, their solubility, and their absorption by charcoal ? 



162. What is marsh gas, and how is it produced in nature? Explain the 



danger of "fire-damp" in coal mines. What is meant by 



"destructive distillation," and from what substances can impure 



marsh gas be produced by this means ? 

 *i63. Determine the percentage of ash in the charcoal. 

 *i64. Determine the percentage increase of weight of wood charcoal 



(previously heated to redness in a tube) on exposure to air. 



