26 



condensing ? Explain how steam may be used to heat a 

 building. 



EXPERIMENT 15. SOLUTIONS 



(a) Place a small deep beaker half full of water in 

 a larger vessel and pack crushed ice or snow around it 



(Fig. 19). With a thermometer 

 note the temperature of the 

 water every minute until twelve 

 or fifteen readings have been 

 obtained. 



(d) Place a second beaker of 

 water in a similar vessel and 

 pack around it a mixture of ice 

 and salt which consists of one 

 part of salt and three parts of 

 ice. Again note the tempera- 

 ture every minute until twelve or 

 fifteen readings have been taken. 

 Does the temperature change 

 with the same rapidity in (a) 

 and (b) ? Why ? 



From your results, tell why salt 



FIG. 19. The water in the inner < 



vessel freezes. is put on ICQ in ice-cream freezers. 



EXPERIMENT 16. NEED OF OXYGEN FOR COMBUSTION 



Mix carefully a small quantity of potassium chlorate and 

 an equal amount of manganese dioxide, and place the mix- 

 ture in a large test tube. Close the mouth of the tube with 

 a one-hole rubber stopper in which is fitted the delivery- 



