30 THE ORIGIN OF ALKALI 



the presence of carbon dioxide react with calcium carbonate, 

 with the formation of sodium bicarbonate. The presence 

 of relatively small amounts of calcium nitrate or calcium 

 chloride in this reaction impedes and finally prevents the 

 formation of sodium bicarbonate. The presence of cal- 

 cium sulphate has no effect in preventing the formation 

 of sodium bicarbonate when sodium sulphate, or a mixture 

 containing sodium sulphate, reacts with calcium carbonate. 

 Sodium nitrate, sodium chloride, and sodium sulphate 

 react with calcium carbonate in the soil with the formation 

 of sodium carbonate (black alkali)." 



Nitrate Formation. - - In alkali areas in many parts of 

 several western states, certain brown-colored spots are 

 found to contain large quantities of nitrates. Headden 

 (10, n) and Sackett and Isham (15) believe that these 

 nitrates are formed within the soil by the action of non- 

 symbiotic nitrogen-fixing bacteria. Stewart and Greaves 

 and Stewart and Peterson (17, 16, 18) are convinced, 

 however, that large quantities of nitrates seep into the 

 soil with the other salts from the country rock and that 

 local nitrogen fixation is a minor matter in the accumulation 

 of sodium nitrate in alkali soils. 



Localization mentioned by Headden is claimed by him 

 to preclude the theory of transportation and concentration 

 in some cases. He states that certain of the spots are in 

 the center of the valley the soil of which is so deep as to 

 preclude the theory of transportation. He also says the 

 ground water about and beneath the spots is not high in 

 nitrates, which again apparently contradicts Stewart and 

 Peterson's theory. 



Concentration by Irrigation Water. Whatever the 

 original source of alkali in the soil, one fact has been well 

 demonstrated. The condition may be greatly aggravated 



