NATURAL WATERS 67 



By hardness is meant the number of grains of calcium 

 carbonate equivalent to the total amount of calcium and 

 magnesium salts present in one gallon of the water. The 

 meanings attached to " temporary " and " permanent " have 

 already been given. Numerically they too are expressed in 

 terms of the equivalent amount of calcium carbonate in grains 

 ^er gallon. 



By albuminoid ammonia in the above table is meant the 

 quantity of ammonia which is evolved from the water by the 

 decomposition of organic nitrogenous substances by distillation 

 with an alkaline solution of potassium permanganate. 



River Water. — Most rivers originate in springs, so that 

 at first their water resembles that of their source. A con- 

 siderable influx of surface-water, however, generally enters 

 the river and alters its composition. The surface-water usually 

 contains less dissolved matter than spring water, but often 

 more organic matter and suspended particles. The composi- 

 tion of the river water greatly depends upon the character of 

 the rocks from which it is collected. When the surface con- 

 sists of igneous rocks or of sandstones the water is usually 

 soft, while in chalk or limestone districts it will be hard. 

 Some rivers — e.g.^ the Trent— are very rich in calcium sul- 

 phate, and to this fact the excellence of the Burton ales has 

 been ascribed. 



The table on page 68 is given by Roscoe and Schorlemmer as 

 representing the average composition of the waters of several 

 well-known rivers. The remarkable softness of the water of the 

 Dee, collected from the granite district in Aberdeenshire, will 

 be noted. 



River water rarely contains excessively large quantities of 

 calcium carbonate, such as occur in some springs, since, owing 

 to its free contact with air, it never retains very large 

 quantities of dissolved carbon dioxide. Calcium sulphate in 

 river water is usually accompanied by sodium chloride and by 

 magnesium salts, 



