WATER 17 



An ion exchange resin that removes anions can be synthesized by con- 

 densing a phenol amine, e.g., CcH4(OH)CHoNHCH3 and formaldehyde. 

 Amberlite IR4B is a commercial product of this type. The removal of 

 anions may be represented by the equation 



CaS04 + 2R0H = Ca(OH). + R0SO4 



The alkalinity thus produced may be neutralized by using the anion 

 exchanger in series with an acid form of cation exchanger (HR), in which 

 case the water is completely demincralized, thus 



Ca(0H)2 + 2HR = CaRo + 2H2O 



The anion exchanger can be regenerated with sodium hydroxide, and the 

 cation exchanger with sulfuric acid. 



A desalting kit for the production of potable water in case of forced 

 landings in overseas flying consists of silver zeolites (AgZ), silver oxide, 

 and barium hydroxide compressed into briquets and placed in a suitable 

 container for filtering sea water. The reactions involved are as follows: 



AgZ + NaCl = NaZ + AgCl 

 Ba(OH)o + MgS04 = Mg(0H)2 + BaS04 



The sodium, chloride, magnesium, and sulfate ions, the chief constituents 

 of sea water, are removed as the insoluble compounds NaZ, AgCl, 

 Mg(0H)2, and BaS04. The capacity of the zeolite material is about ten 

 times its volume of sea water. 



The above discussion of ion exchangers is merely a bare outline of the 

 subject, and the interested student is referred to the books listed at the 

 end of the chapter for complete information on this complex and rapidly 

 developing field of work. 



REVIEW QUESTIONS ON WATER 



1. Would you expect the young leaves of a growing plant to be higher or lower 

 in water content than the fully developed leaves? Explain. 



2. Arrange these materials in ascending order of water content: milk, blood, cab- 

 bage, saliva, strawberries, fish. (Consult Tables 2-1 and A-1.) 



3. Explain the terms "bound water" and "free water." 



4. Explain the term hydrogen bond. With which other elements is it associated? 

 Consult the index. 



5. What changes in composition would you expect to find in wheat plants ana- 

 lyzed in September and again in December? 



6. What is the daily water requirement of an adult? Name some of the chief 

 functions of water in the body. 



7. Explain how clothes moth lar\ae get their water. Can you name another 

 insect or living organism that gets its water in the same way? 



8. What is meant by "metabolic water"? What is the approximate contribution 

 of this Vv'ater to the total intake? 



