92 IRRIGATION PRACTICE 



The first column shows the average composition (rarer 

 elements being excluded) of river waters for the world. 

 All the elements necessary for plant-growth are present. 

 The carbonic acid, combined chiefly with calcium, is in 

 largest abundance. Sulfuric acid, in combination with 

 calcium, magnesium, sodium and possibly potassium, is 

 also present in large abundance. Chlorine is third in 

 abundance. Even nitric acid, vitally important for plant- 

 growth, is present in small quantities. In the three fol- 

 lowing columns are analyses of the waters of three great 

 rivers of western America, used largely for irrigation pur- 

 poses. All the necessary plant-foods are present, but in 

 very different proportions, which, undoubtedly, will 

 affect, differently, the conditions of plant-growth. In 

 column 5 is the average composition of ocean waters as 

 determined by the Challenger expedition. It differs 

 materially from the analysis in column 1 which is a world 

 average for river water. The carbonic acid has practically 

 disappeared, no doubt precipitated by the lime, and the 

 sodium and chlorine have increased tremendously. In 

 column 6 is an analysis of the water of the Great Salt 

 Lake, which is a body of water practically saturated with 

 common salt. It resembles ocean water, but carbonic 

 acid is totally absent; the proportion of calcium and 

 magnesium lower; of potassium higher. 



66. Classification of natural waters. Considering 

 the composition of the soluble materials held by natural 

 waters, especially those used in irrigation, they may be 

 classified as follows: Those rich in chloride of sodium are 

 called chloride waters; those rich in sulfates, especially 

 of sodium and calcium, are sulfate waters; those rich in 

 carbonates, especially of sodium, are carbonate waters; 

 those rich in borates are borate waters; those rich in free 



