120 QUESTIONS ON THE 



199. What part of the earth's surface does the ocean 

 cover ? 



200. Is there any air in water ? 



201. What part of the ocean is the saltest, and why ? 



202. What causes the impurity of rain water ? 



203. Why is the Thames water preferred for long 

 voyages ? 



204. Which putrefies soonest, spring water or river 

 water ? 



205. What causes the hardness of spring water? 



206. Where have springs of fresh water been disco- 

 vered in the sea ? 



207. Which is most capable of being confined, water 

 or air ? 



20S; What is the boiling point of water when the ba- 

 rometer is at 29 inches, and when at 31 inches, and what 

 is the cause of the difference ? 



209. Where are the chief hot springs ? 



210. What is the mean specific gravity of water? 



2 11. What causes the specific gravity of water to 

 vary? 



212. To what cause may Earthquakes and Volcanic 

 eruptions be often assigned ? 



213. Which may be made to displace the greater 

 weight, a pound of gunpowder, or a pound of water ? 



214. What causes that motion of water called boiling ? 



215. Give an example of the surprising power of steam- 

 engines.. 



216. How much rarer than water is steam at 212 ? 



21 7. Explain the theory of boiling. 



218. How many balls in a day of 16 hours would 

 Perkins's steam-gun discharge, if it could continue with 

 the same rapidity that it does in the first four seconds 

 of its action ? 



219. Required the weight of a tun of water. 



220. Required the weight of a cube of three feet of 

 water. 



221. What quantity of water might be thrown up by 

 St. Winifred's Well in a day of 24 hours ? 



