562 



Journal of Agricultural Research 



Vol. X, No. II 



Table XXIII. — Reaction between 20 per cent solutions of sodium nitrate and calcium 

 carbonate in the presence of calcium, nitrate and carbon dioxid at atmospheric pressure 



Table XXIV. — Reaction between 10 per cent solutions of sodium chlorid and calcium, 

 carbonate in the presence of calcium chlorid and carbon dioxid at atmospheric pressure 



Unquestionably a great part of the black alkali found in the arid and 

 semiarid West is due to the action of the sodium salts on calcium car- 

 bonate in the presence of more or less carbon dioxid. Sodium bicar- 

 bonate is thus formed and carried to the surface as such and there, upon 

 the evaporation of water, gives up part of its carbon dioxid and becomes 

 the normal carbonate, or black alkali. The wet areas of the lowland, 

 where black alkali is known to be more prevalent, lend themselves very 

 well to its formation. Here we have water which is necessary for bacte- 

 rial action and which tends to hold the carbon in solution and prevent 

 its rapid escape into the atmosphere. 



In the consideration of black alkali its formation under field condi- 

 tions in a practically saturated solution of the sodium salt is not an 

 overdrawn conception. When the sodium salt exists in any appreciable 

 quantity in a soil it will at some time or other, by alternate dilution 

 and evaporation, exist in all the different concentrations, from a dilute 

 solution up to the salt crystal itself. This will happen in a soil that is 

 irrigated regularly, saturated with water, and then allowed to dry down 

 to near the wilting point between irrigations. 



EXPERIMENTS WITH SAND AND SOIL 



A large sample of soil was taken from the grounds of the new Citrus 

 Experiment Station at Riverside, California, sifted through a 2 mm. 

 sieve, mixed and dried in the sun for analysis. This soil, when shaken 



