120. , GENERAL SCIENCE 



5. A block of wood 8 inches high sinks 4 inches in water. 

 What is the density of the wood? 



6. Suppose the above block of wood sinks 5 inches in alcohol, 

 what is the density of the alcohol? 



7. A stone weighs, 15 pounds in air and 10 pounds in water. 

 What is the density of the stone? 



8. Why does a stone seem lighter under water? 



9. Explain the principle of the hydraulic press. 



10. Would a piece of iron float in melted copper? 



11. What solids sink in mercury? 



12. A solid weighs 25 grams in air and 20 grams in water. 

 What does an equal volume of water weigh? What is the density 

 of the solid? 



13. How much water does a floating piece of wood displace? 



14. An iron weight weighs 10 pounds in air and 140 ounces in 

 water. What is its density? 



15. A fresh egg sinks in pure water. Why ? Why does it not 

 sink in strong brine? How can you find the density of an egg? 



16. How may you determine the density of a piece of butter? 



17. How could Archimedes tell whether or not Hiero's crown was 

 pure gold? 



Common Uses of Water. Great quantities of water 

 are used daily in our large cities, and the problem of 

 supplying pure and wholesome water for the people of a 

 great city like New York is by no means a small one. 

 Each city has a different problem, depending upon its 

 location, the nature of the underlying soil and rock, and 

 the amount of water needed. Many cities pump the 

 water from deep wells near by ; others carry the water in 

 immense tubes for miles from some source which has a 

 higher altitude than the city to be supplied ; other cities 

 like Chicago or Cleveland take the water from the lakes 

 near by; still others use the rivers (Figure 107). 



Hardness of Water. Water is usually spoken of as 

 hard or soft. Hardness of water may be measured by its 

 soap-consuming power. The hardness of water depends 



