394 SMITH'S INTERMEDIATE CHEMISTRY 



used as ingredients in fireworks and signal lights. Barium 

 sulphate is used in making white paint (" permanent white "). 



Exercises. 1. Why can not lime-water be kept in an open 

 bottle? 



2. Why does whitewash become so firmly attached to the wall? 



3. What is the percentage of nitrogen in nitro-lime, assuming 

 100 per cent efficiency of conversion? 



4. Make equations for the action of sodium palmitate: (a) 

 upon calcium bicarbonate; (b) upon magnesium sulphate. 



5. In softening water: (a) what would be the objection to 

 using an excess of milk of lime; (b) why is prolonged stirring 

 required (p. 389); (c) why must the precipitate be removed by 

 filtration? 



6. Explain why wood ashes are sometimes used to soften water, 

 and how they act. 



7. Make equations for the action of chlorine upon quicklime- 



8. Why does fluorite lower the melting-point of a slag? 



