178 SCIENCE OF COMMON THINGS. 



Force of expansion. Ice, why lighter than water. 



If we take the exact dimensions in length, breadth, 

 and thickness of any substance when cold, and measure 

 it again when strongly heated, it will be found to have 

 increased in every direction. 



117*O Do bodies expand with the increase of heat, and contract upon its 

 withdrawal, with any degree of force f 



Yes ; the force with which bodies contract and ex- 

 pand under the influence of heat is apparently iwesist- 

 ible, and is recognised as one of the greatest forces in 

 nature. 



117*1 What peculiarity exists in the effect of heat upon the bulk of so^* 

 fluids ? 



That at a certain temperature increase of heat causes 

 them to contract, and its diminution makes them ex- 

 pand. 



117*3 What classes of liquids exhibit this peculiarity f 



Those only which increase in bulk in passing from 

 the liquid to the solid state^ and this change is remarked 

 only within a few degrees of temperature above their 

 point of congelation. 



117*3 What is a noted example of this exception to the general laios of 

 Jieat? 



Water / ice swims upon the surface of water, and 

 therefore must be lighter, a convincing proof that wa- 

 ter in the act of freezing must expand. 



117*4 Why is the ice produced ly the freezing of sea water ahvays 

 fresh and free from salt ? 



Because water, in freezing, if in sufficient quantity 

 to allow freedom of motion to its particles, expels all 

 impurities and coloring matters. 



117*5 If a solution of indigo be frozen, why will the ice formed be clear 

 and colorless f 



Because the water in which the indigo was dissolved 

 expels all the blue coloring matter while freezing. 



117*6 Why are blocks of ice generally filled with air-bubbles f 



Because the water, during the act of freezing, expels 

 the air contained in it, and many of the liberated bub- 

 bles become lodged and imbedded in the thickening 

 fluid. 



