PHYSICO-CHEMICAL PROCESSES 155 



9. What is filtration? Has it any industrial importance? 



10. Name the three methods by which substances are purified. 



11. Explain crystallization. 



12. Explain how large crystals may be obtained; "mealy" 

 crystals. 



13. What is the meaning of the term " water of 'crystallization "? 



14. Give the percentage of water of crystallization in "washing 

 soda," Na 2 C0 3 .10H 2 0. (Refer to table of atomic weights in 

 Chapter XL) 



15. What is the meaning of sublimation? 



16. What are the two kinds of coal? 



17. Explain the meaning of rancidity; putrefaction; fermen- 

 tation. 



18. What are germs? 



19. Explain why metals are sometimes found as oxides; sul- 

 phides. 



20. What is the difference between granite, sandstone, and 

 marble? 



21. Name the different classes of lubricants. State the advan- 

 tages and disadvantages of each class. 



22. Explain the difference between crystalline and amorphous. 



