180 THE LUKE OF THE LAND 



THE ROLE OF WATER IN SOIL, MAKING. 



" Attention has also been called to the solvent action 

 of water. It is well to consider in this respect the fact 

 that pure water is not, as a rule, so good a solvent as 

 impure. Water especially which contains carbon di- 

 oxid in solution, or traces of organic acids, or traces of 

 phosphoric and nitric acids, acts much more vigorously 

 on many rock materials than pure water could possibly 

 do. The water of springs and wells is not pure. It 

 contains in solution mineral matters and often a trace 

 of organic matter. The organic matter comes from 

 contact with vegetable matter and other organic ma- 

 terials near the surface of the earth. The mineral 

 matter is derived from the solvent action of the water 

 and its contents on the soil and rocks. 



" The expression ' hard ' or ' soft ' applied to water 

 indicates that it has much or little carbonate of lime 

 and magnesia or sulfates of the same bases in solution. 

 Water containing much carbonate of lime (or lime and 

 magnesia) in solution is usually more or less charged 

 with carbon dioxid. When boiled this gas is driven 

 off and the carbonates precipitated. This kind of hard- 

 ness is called temporary. When surface and spring 

 waters are collected into streams and rivers they still 

 contain in solution the greater part of the mineral mat- 

 ters which they at first carried. 



" When waters have more than 600 parts of mineral 

 matter per million they are not deemed suitable for 

 drinking waters. Mineral waters, so called, are those 

 which carry large quantities of mineral matter, or 

 which contain certain comparatively rare mineral sub- 

 stances which are valued for their medicinal effects. 



" The analysis of spring, well, or river waters will 



