72 ANSWERS TO PRACTICAL QUESTIONS. 



7. Since " all the rivers flow to the sea/' ivliy is it not 

 full? 



Because of the constant evaporation from its surface. 



8. What is the cause of the tonic influence of the sea- 

 breeze? 



There are traces of certain minerals which probably give to 

 the sea-breeze a bracing influence. The air from the ocean is 

 also, doubtless, highly ozonized. It is free from the contamina- 

 tions that so often make the atmosphere of the cities and parts 

 of the country unhealthy. 



9. When fish are taJcen out of the water, and thus 

 brought into a more abundant atmosphere, ivhy do they 

 die? 



Fish inhale O through the fine, silky filaments of their gills. 

 When a fish is drawn out of H 2 O, these dry up, and it is un- 

 able to breathe, although it is in a more plentiful atmosphere 

 than it is accustomed to enjoy. 



1 0. Do all fish die ivhen brought on land ? 



No. Some fish have an apparatus for moistening their gills. 

 They can therefore crawl about in the grass, and even migrate 

 from one stream to another. 



1 /. What weight of water is there in 1OO Ibs. of sodium 

 sulphate (Na 2 SO 4 , 1OH 2 O), or Glauber 9 s salt? 



10H 2 O : Na s SO 4 , 10H,O : : x : 100 Ibs. 

 180 : 322 : : x : 100 Ibs. 



322 x = 18,000 Ibs. 



a = 55.9 Ibs. (H 2 O). 



J2. Wliat weight of water in a ton of alum (KA1 9 

 12H 2 O}? 



12H 3 O : KA1, 2SO 4 , 12H 2 O : : x : 2,000 Ibs. 

 216: 474.5 : : x : 2,000 Ibs. 



474.5 x = 432,000 Ibs. 



x = 910.4 Ibs. (H 2 O). 



13. How does the air purify running water? 



