9 AN8WE&8 TO PRACTICAL QUESTIONS 



12. What weight of water in a ton of alum (KA1,2SO 4 , 

 i2H 2 O)? 



iaH 2 O : KA1, 2 SO, i2H 2 O : : x : 2000 Ibs. 

 216 : 474-5 '. : x \ 2000 Ibs. 



474.5 x = 432000 Ibs. 



x 910.4 Ibs. (H a O). 



13. How much water would it require to furjiish enough 

 H to change 5 Ibs. of nitric anhydride to nitric acid? 



Find (i) how much HNO 3 could be made from 5 Ibs. 

 of N 2 O 5 (see Chemistry, page 44, note); (2) how much 

 H 2 O is contained in that amount of HNO 3 . The differ- 

 ence between the weight of the nitric anhydride and that 

 of the nitric acid will show the amount of water required 

 to furnish the H. 



(i). N 2 O 5 : 2 (HNO.) : : 5 Ibs. : x. 

 108 : 126 : : 5 Ibs. : x. 

 108 x 630 Ibs. 



x = 5.833 Ibs. (HNO 3 ). 



(i). 5-833 Ibs. (HNO 3 ) - 5 Ibs. (N a O.) = .833 Ib. (H a O). 



14. How does the air purify running water? 



The O contained in the air absorbed by the H 2 O 

 oxidizes the organic substances, which are the most 

 dangerous impurities. 



15. What is the action of potassium permanganate as a 

 disinfectant ? 



It gives up its O to oxidize the organic impurities. 



1 6. Why does lime sometimes soften hard water when 

 added to it ? 



(See Key^ page 50, Question 4.) 



17. What weight of H can be obtained from a gallon 

 of water 1 



