62 



SEA-WATER. 



is the great promoter of combustion, forms water, a 

 compound which we always regard as the greatest 

 enemy to fire or combustion. 



71. The purest kind of water which occurs naturally 

 is rain-water, for all others, such as spring, river, or 

 sea-water, are more or less contaminated or rendered 

 impure by substances dissolved in them. Thus sea- 

 water contains, along with other matters, a large 

 quantity of common salt, which in some places is pro- 

 cured from it by exposing it in shallow pits to the heat 

 of the sun: this causes the water to evaporate, and 

 leaves the salt behind. 



72. The composition of sea-water from different 

 parts of the world is found to vary slightly. The 

 following table shows the composition of 100,000 parts 

 of sea-water from the English Channel. (Schweit- 

 zer.) 



100,000 



73. Water may be artificially purified by distil- 

 lation; when heated and raised into vapor, all the 



