268 GENERAL SCIENCE 



11. How many cubic feet of water do you displace when you dive? 



12. How many times heavier is gold than water? 



13. How could you tell whether your gold ring is pure or not? 



14. Try to find out. 



15. Why will a submarine float? 



16. What must be done to make it sink? 



17. What would be about the pressure per square inch of the 

 water at the faucet in the sink, if the water tank is 12 feet above the 

 faucet and nearly empty? What would be the pressure if there were 

 7 feet of water in the tank? 



18. Why will a board enable a person to walk over a swampy place? 



19. Why is a drowning person more likely to sink if he throws 

 up his arms? 



20. Why is a fish with a swimming bladder able to rise and 

 sink in water? 



CLEANING OF FABRICS 



Water as a Solvent. Water is a solvent for many things, but for 

 such substances as grease, oil, fat, tar, etc., ether, gasoline, and ben- 

 zine are often used because they dissolve fats or oils which water 

 will not. Whenever oil is shaken with water it breaks up into 

 little fine bubbles (globules)' which give the water a -turbid appear- 

 ance. Soon, however, the water and oil will separate. If a substance 

 had been added to the water to prevent the oil and water sep- 

 arating when the oil and water were mixed, the result would be 

 called an emulsion. Soap is one of the best emulsifying agents. 

 Dirt or spots on clothing which cannot be taken off with water 

 usually are of a fatty or oily nature. When soap is added to the 

 water the fat emulsifies into fine drops which are carried out of 

 the cloth. 



Cleaning of Fabrics. Many people use ether, benzine, gaso- 

 line, turpentine, and other dangerous liquids for cleaning. Carbon 

 tetrachloride is the safest solvent, since it is non-inflammable. 

 A good combination for removing fats and oils from clothing is a 

 mixture of carbon tetrachloride with turkey red. It may be used 

 with cold water in the laundry as a substitute for soap. It readily 

 removes grease from the hands when used with cold water. 



