122 CHEMISTR V FOR A GRIC UL TURAL STUDENTS 



The Sulphates. 



66. What are Glauber's salt, Epsom salt, gypsum, selenite, potash alum, 

 white vitriol, green vitriol, and blue vitriol ? Give a general 

 method by which they can all be produced. 



6*]. What is meant by the ''efflorescence" of a salt, and to what is it 

 due ? At what temperature is the water of crystallisation of a salt 

 usually given off? What is meant by an "amorphous" substance? 



68. In what respect does plaster of Paris differ from gypsum ? Explain its 



use as a plaster. When is plaster of Paris said to be " dead burnt " ? 



69. In order to obtain a salt in a well-crystallised state, how would you 



proceed? In what form does alum crystallise? Draw a perfect 

 alum crystal. 



70. Name the groups, the metals of which are attacked by dilute sulphuric 



acid. Give one reason why zinc and iron are more easily attacked 

 by dilute sulphuric acid than they are by water. 



71. With what metallic sulphate are the crystals of zinc sulphate iso- 



morphous? In what other respects do the two metals resemble 

 each other ? 



72. What is the action of metals upon strong sulphuric acid when heated ? 



What is meant by an "oxidising" and a "reducing" agent? 

 Give examples. 

 *]2f. Discuss the use of the terms "sulphuric acid" and "sulphate of 

 hydrogen," "sulphate of soda" and "sulphate of sodium." In 

 what respects is the term "sulphate of sodium" preferable? 



74. What is meant by "equilibrium" in solution. State what changes 



might take place when the solutions (i) of a base and a salt, (2) 

 of an acid and a salt, and (3) of two salts, are respectively mixed 

 together, and point out what are the circumstances under which there 

 will be no equilibrium, but complete reaction between the mixed sub- 

 stances. Give examples to illustrate each of the six possible cases. 



75. Describe a method for preparing oxide of magnesium from Epsom 



salt ; also for preparing sulphurous anhydride from sulphite of 

 sodium ; also for preparing sulphate of barium and caustic soda 

 from sulphate of sodium and baryta. Give equations. To prepare 

 I gram of copper oxide, how much blue vitrol must be used ? 



^76. Which of the salts contains water of crystallisation? (Sulphate of 

 calcium and sulphate of barium.) 



^77. Identify the salts. (Sodium sulphite and ferric sulphate.) 



^78. Prepare a specimen of magnesia from the Epsom salt. 



*79. From the copper and sulphuric acid prepare a well - crystallised 

 specimen of copper sulphate. 



