284 ELEMENTARY GENERAL SCIENCE or. xx 



3. What are phosphates, and how may they be obtained ? 



4. How is ordinary phosphoric acid obtained ? What is its effect 

 upon caustic soda ? 



5. Give an account of the preparation and characteristic properties 

 of phosphoretted hydrogen. What precautions have to be strictly 

 observed in its preparation ? 



6. Describe, with diagram, an experiment to find the relative 

 weights of phosphorus and oxygen which combine during the com- 

 bustion of phosphorus. 



7. When phosphorus has been kept for some time it maj 7 not 

 have the appearance and properties which are usually ascribed to it. 

 Why is this ? 



8. W T hat oxides of phosphorus are there '? How are they obtained 

 and how do they differ ? 



9. For what purposes may the higher oxide of phosphorus be used 

 in chemical work, and to what property is its use due Y 



10. Give a short account of the mode of production of phos- 

 phorus. For what purposes is phosphorus chiefly employed ? 



11. How is it that whereas only one salt is obtained by the action 

 of caustic soda upon hydrochloric acid, three salts are obtainable 

 from phosphoric acid ? 



12. Phosphoretted hydrogen as ordinarily prepared is spon- 

 taneously inflammable. It may however be so prepared that it is 

 not spontaneously inflammable. To what is the difference due, and 

 how may the first gas be converted into the second ? 



