Sept. 10, 1917 



Formation of "Black Alkali" 



549 



On the other hand, there is an appreciable reaction between sodium 

 sulphate and calcium carbonate, even in a saturated solution of calcium 

 sulphate, as is shown in Table VII. The data in Tables V, VI, and VII 

 are shown graphically in figure 2. 



EFFECT OF GYPSUM UPON THE FORMATION OF SODIUM CARBONATE 



As the soils of the West, as well as many of the irrigation waters, 

 frequently contain gypsum in appreciable amounts, the reaction between 

 the alkali salts so- 

 dium nitrate, sodium 

 chlorid, and sodium 

 sulphate with cal- 

 cium carbonate usu- 

 ally takes place in the 

 soil in the presence of 

 more or less calcium 

 sulphate. Tables 

 VIII, IX, and X and 

 figure 3 showtheefifect 

 of this salt upon the 

 formation of black alkali. As outlined in the tables, calcium sulphate was not 

 added in excess, but a saturated solution containing 2.1 gm. per liter was 

 used in preparing the different numbers. This was necessary in order to 

 have a definite amount of calcium sulphate in the solutions, as the solubility 

 of this salt increases very rapidly in the presence of certain sodium salts. 



Table VIII. — Reaction between sodium nitrate and calcium carbonate in the presence of 



calcium sulphate 



I 



(^ O .^ /O /S ^O ^S 30 '3S 'i'O ^O^ so SS GO 



Fig. 3.— Graphs showing the effect of gypsum on the formation of sodium 

 carbonate in the reaction of calciixm carbonate with sodium chlorid, 

 sodium nitrate, or sodum sulphate. 



Table IX.- 



-Reaction between sodium chlorid and calcium carbonate in 0.21 per cent 

 solutions of calcium sulphate 



