62 SCIENCE OF COMMON THINGS. 



Why 1ce floats and iron sinks in water. Platinum and hydrogen. 



CHAPTER II. 



SPECIFIC GRAVITY". 



373 Why does ice float upon water f 



Because it is lighter than water. 



374 Why does iron sink in water f 



Because it is heavier than water. 



37*5 If we put a piece of ice in alcohol, it sinks ; if we put a piece, of 

 iron upon quicksilver, it floats : why is this f 



Because the ice is heavier than the alcohol, and the 

 iron is lighter than the quicksilver. 



37*6 What do we mean, when we say that ice is lighter than iron ? 



We mean that, taking equal bulks of each, the former 

 weighs less than the latter ; and when we say that 

 quicksilver is heavier than water, we mean that, in 

 equal volumes, as a pint, for instance, the quicksilver 

 has a greater weight than the water. 



377 What, then, is specific gravity f 



It is the weight of a body compared with the weight 

 of an equal bulk of water. 



378 How does it differ from ordinary or absolute weight f 



In absolute weight no regard is paid to the volume or 

 bulk of substances. In specific weight, a given bulk 

 or volume is compared with an equal volume or bulk 

 of water. 



379 What body has the greatest specific weight f 



Purified platina, which is 22 times heavier than an 

 equal bulk of water. 



380 What substance has tlie smallest specific weight f 



Hydrogen gas, which is 12,000 times lighter than an 

 equal bulk of water. 



381 Why will an egg float in strong brine, and not in fresh water f 



Because the solution of a solid in any liquid increases 

 its density, or its specific gravity : the addition of salt 



