8 



value for irrigation purposes. The following analyses show the com- 

 position of the water during three weeks when it was most concentrated' 

 Chemical analyses of drainage ivater from the Toft-Hansen reclamation tract. 



Of the salts shown to be in the drainage water about three-fourth! 

 may be regarded as harmful. The remaining 25 per cent are princi- 

 pally salts of lime and magnesium, which would precipitate out by 

 evaporation as the water concentrates upon a field. Sodium carbonate 

 or black alkali, although the predominating salt found in the surface ol 

 the soil, is not present in any quantity in the drainage water. Sodium 

 carbonate has never been found in the drainage water as it comes from 

 the tile, but after the water stands and aerates this salt forms by the 

 decomposition of the sodium bicarbonate, so that though we have 

 removed large quantities of black alkali from the soil it has never 

 appeared as such in the drainage water. The explanation of this is 

 that the sodium carbonate or black alkali seldom exists as such except 

 in the first few inches of surface soil, and as soon as it is washed into 

 the soil it absorbs carbonic acid gas, with which the soil air is always 

 more strongly charged than is the atmospheric air, and forms the much 

 less harmful sodium bicarbonate. 



Numerous examples can be given where waters of greater concentra- 

 tion than this drainage water are successfully used for irrigation, both 

 in the United States and in other countries, and it can be definitely 

 stated that water of this character can be used for irrigation upon any 

 soil where adequate underdrainage is maintained. If such water were 

 used upon poorly drained soil the inevitable result would be an accum- 1 

 ulation of alkali at the surface. The drainage water from the entire! 



