278 SCIENCE OF HOME AND COMMUNITY 



there is danger that water will freeze. On the whole, how- 

 ever, the air system is much less effective than the water 

 system. To avoid the danger of overheating, nearly all 

 makes of cars use the water system. 



In the water system of cooling, the cylinder is surrounded 

 by a jacket kept filled with water. The circulation of this 

 water is maintained in either of two ways, the natural system 

 or the pump system. In the natural system, the water 

 circulates as in a hot- water heating system, described on 

 page 7, the hot water rising and the cold water flowing in 

 to take its place. In the other system, the water is forced 

 around through the tubes by means of pumps operated 

 automatically by connection with some part of the engine. 

 The water is cooled by passing through radiators exposed 

 to air and containing many tubes which give a large cooling 

 surface. The air is forced against these radiators by means 

 of fans. In winter alcohol is added to the water to prevent 

 freezing. 



DEMONSTRATION 20 



Purpose. To show how the gas engine works. 



Apparatus. Two large-mouth bottles, pan, coffee pot, 

 Bunsen burners, small gas engine or model of one, induction 

 coil, cells. 



Directions. I. To show the need of a mixture of gases to cause 

 an explosion. Fill an ordinary pan about a third full of water. 

 Fill one large-mouth bottle with water and another half full. 

 Invert them both in the pan of water. Connect a piece 

 of rubber tubing with the gas jet. Put the other end over the 

 edge of the pan and under the mouth of the bottles. Then turn 

 on the gas till the water is forced out of the bottles. Then 

 turn off the gas. Take out the bottles and put a piece of card- 

 board over the mouth of each. Bring a lighted match to the 

 mouth of the bottles after taking off the covers. What is the 

 difference in the action of the two? What does this show? 

 Partially fill the bottles again with water to see what propor- 

 tion of air and gas give the loudest explosion. If illuminating 



