MINERAL WATERS 63 



rain in districts where much coal is burnt is of gi-eat impor- 

 tance as affecting the growth of plants, particularly of the 

 grasses and certain trees. In addition to its direct injurious 

 effect upon the foliage, it exerts a deleterious action upon the 

 soil, tending to remove the calcium carbonate or other basic 

 material, to interfere with the growth of micro-organisms, e.g.y 

 those of nitrification, and to promote " sourness," so unfavour- 

 able to the growth of most useful plants. Grass land under 

 such circumstances often becomes almost sterile, the last plants 

 to succumb to the unfavourable conditions being the " sorrel " 

 or Kour dock." 



The combined nitrogen brought down by the rain has been 

 already referred to (see Chap. II. p. 30). 



Spring* Water. — The water issuing from springs varies 

 greatly in the amount and nature of the dissolved matter 

 which it contains. If this be small, and not possessed of strong 

 taste or odour, the water is described as fresh water ; but if a 

 large quantity of dissolved matter be present, or if the water 

 possess pronounced taste, odour, or medicinal properties, it is 

 known as a mineral water. 



Most spring-waters contain the following substances, but in 

 very varying amounts : 



(1) Calcium and magnesium carbonates dissolved in excess 

 of carbon dioxide. 



(2) Calcium or magnesium sulphate. 



(3) Sodium or potassium chloride. 



(4) Alkaline silicates. 



(5) Dissolved gases — oxygen, nitrogen, and especially carbon 

 dioxide. 



Calcium and magnesium carbonates are almost insoluble in 

 water, but if the water contain carbon dioxide the readily 

 soluble bicarbonates are formed : 



CaCO, + H,0 + CO, = Ca(HC03V 



Calcium bicarbonate 



Such action occurs largely in all limestone or chalk districts. 



