134 GENERAL SCIENCE 



Experiment 37. Fill an ordinary large-mouthed bottle with 

 water and fit it with a one-hole rubber stopper. Insert a glass tube 

 in the stopper and crowd the stopper down until the water fills the 

 tube. Now place the bottle in a freezing mixture of ice and salt 

 and watch the contraction and expansion of the water. What is 

 the first change noticed? At what temperature does water cease 

 to contract and begin to expand ? Watch the experiment until the 

 whole mass of water in the bottle is frozen. 



Vaporization. - - The changing of a liquid to a gas is 

 called vaporization. Slow vaporization is called evapora- 

 tion. It takes place at all temperatures below the boiling 

 point. Ebullition or boiling takes place at a definite tem- 

 perature, and if the pressure on the liquid does not change, 

 the temperature will remain constant until the liquid 

 is completely vaporized. 



Boiling. While evaporation takes place only at the 

 surface of the liquid, boiling takes place throughout the 

 entire mass. It is interesting to watch the water in a 

 beaker as it approaches the boiling point. From where 

 do the air bubbles come that gather on the walls of the 

 beaker? Do the first bubbles of steam get smaller or 

 larger as they rise in the liquid? What causes the agi- 

 tation of the liquid? What becomes of the water that 

 disappears? If a thermometer is placed in the liquid it 

 will probably read less than 100. Why? 



Determine the boiling point of alcohol. 



Boiling Points at Standard Pressure 



Ether . . . ... . .". 38 Water ... . . . 100 



Chloroform ....... 60 Mercury ....... 350 



Alcohol 78 Sulphur 440 



Benzine ........ 80 Zinc 1050 



Relation of Boiling Point to Pressure. Of course the 

 atmosphere is exerting a pressure on the surface of a 



