52 FIRST YEAR SCIENCE 



gas. Examples of these are : the solid metal ball, the 

 liquid water, the liquid metal mercury, and the gaseous air. 

 These have already been dealt with experimentally. Al- 

 most every one knows that water is a liquid, or a solid, 

 ice, or a gas, steam, depending only on the temperature to 

 which it is subjected. It is not so generally known that 

 the state of all other substances depends also upon their 

 temperature. 



Many substances are capable of existing in all three 

 states. Iron, for instance, may be solid as we ordinarily 

 see it, or liquid as it comes from a blast furnace, or a gas, 

 as it exists in the tremendously hot atmosphere of the 

 sun. Substances usually expand in volume as they change 

 from the solid to the liquid state and they always do as they 

 change from the liquid to the gaseous. Ice is a notable 

 exception to the general rule, since when water freezes its 

 volume increases. If it were not for this, ice would not 

 float. Metals that are suitable for casting must have the 

 property of expanding when cooling or at least of shrink- 

 ing but a trifling amount. This is a most valuable prop- 

 erty of type metal and cast iron. 



27. The Transference of Heat. Experiment 23. Cut off 



15 cm. of No. 10 copper and No. 10 iron wire and the same length of 



glass rod of about the same diameter. Holding each of these by one 



end place the opposite end in the flame of a Bunsen burner. Which 



of the three conducts the heat to the hand first? 



Experiment 24. Fill a test tube about f full of 

 cold water. Holding the tube by the bottom carefully 

 heat the top part of the water until it boils. Be sure 

 that the flame does not strike the tube above the water, 

 Fig 27 else *he -tube wi U break. A little piece of ice in the 

 bottom of the test tube makes the action more apparent. 

 A bit of wire gauze or a wire stuifed into the test tube will prevent the' 

 ice from coming to the surface. Water conducts heat poorly. The 

 hot water does not sink. It must be lighter than the colder water. 



