12 



CHEMICAL COMPOSITION OF THE ALKALI. 



The alkali of this portion of the desert is all of the white kind, 

 principally the chlorid of potassium and sodium. Lime is present 

 both as sulphate and carbonate. No crops except sorghum and millet 

 have as yet been grown, so the exact limitations for the different crops 

 for this area were not established, although they certainly could not 

 withstand a great deal more than the crops elsewhere. If the soils 

 are kept well drained there is enough gypsum in the soil and water 

 to preclude all possibility of there ever being an accumulation of the 

 black alkali. 



As the area is now below sea level, and the soils were most likely 

 deposited in salt or brackish water when this was a part of the sea. 

 and the alkali is principally common salt, the principal salt of the sea, 

 we may directly conclude that the major part of the alkali came from 

 the sea water, this alkali simply staying in the soil because the rainfall 

 was insufficient to wash it out. The floods from the Colorado have 

 brought in other salts, particularly sulphates, and much changed the 

 chemical composition of the salts from their original composition as 

 deposited from the sea. 



The following table shows the results of the analysis of a mixture of 

 eight samples of alkali crust collected from various places in the desert: 



Analysis of mixture of eight samples of alkali crust from Imperial area, California, /<//- 

 liineif by a conventional method. 



Per cent. 



CaSO 4 (calcium sulphate) 9. 91 



MgSO 4 (magnesium sulphate) 9. 02 



Na-^SOj (sodium sulphate) 33 



KC1 (potassium chloride) 30. 02 



NaHCO 3 (sodium bicarbonate) 9. 59 



NaNO 3 (sodium nitrate) 8. 91 



NaCl (sodium chloride) 32. .> 



100 



The alkali exists either in the soil or subsoil throughout the area 

 mapped. In many places where the soil is of open, porous nature this 

 alkali has been washed out of the surface soil down into the subsoil, 

 and in the case of the more sandy soils will very likely stay in the 

 subsoil too deep to damage shallow-rooted crops, unless the soils are 

 so filled up with water that the capillary power of the sandy soils can 

 raise the standing water to the surface. 



