LIQUIDS AND THEIR PROPERTIES 83 



the solvent. The substance has dissolved and is thus shown 

 to be soluble. 



Water is a solvent for many substances, but not for others, 

 such as fat, wax, and gum. Alcohol dissolves many solids 

 which are not soluble in water. Benzine is another 

 solvent. It is their ability to dissolve grease, gums, and 

 such substances that makes alcohol and benzine useful as 

 cleansers. 



Metals are not soluble in water or in alcohol, but dis- 

 appear after a time in acids. In such a case the product is 

 not a mixture, as in the case of sugar and water, but a new 

 compound. If a solution of sugar and water is boiled until 

 the water has all evaporated, sugar will remain in solid form. 

 But the liquid formed by the action of the acid upon the 

 metal, on being evaporated, will not leave the original metal 

 but a very different solid in the form of crystals. 



89. Natural Waters. Raindrops are nearly pure water; 

 but while the rain water soaks through the ground, various 

 minerals become dissolved in it. These minerals in very small 

 quantities are found in the water of wells, springs, and rivers. 

 Water also dissolves gases and some organic matter from the 

 ground. Many of these dissolved impurities are harmless, 

 but some are sources of disease. It is best, therefore, not 

 to drink well-water or brook-water which has passed near 

 houses and barns. Such water can be made safe for drinking 

 by boiling it for ten minutes or more and then cooling it. 

 Injurious organisms, such as disease germs, are destroyed by 

 long continued heat. 



Natural waters are not pure, though they may be harm- 

 less. Nearly pure water can be obtained by distilling the 

 water of springs, rivers, and even the sea. The dissolved 

 mineral matter does not vaporize but remains as a solid 

 after all the water has evaporated. The distillate may 

 contain some of the gases which were dissolved in the 

 water, and so it is not perfectly pure. 



