Sept. lo, 191 7 



Formation of "Black Alkali" 



561 



ticular type of alkali. It will be noted that the presence of calcium 

 sulphate materially affected the reaction in the case of sodium nitrate 

 and sodium chlorid; but, as might be expected, no effect was in evidence 

 in the case of sodium sulphate or the mixture containing sodium sul- 

 phate, since in the reaction of sodium sulphate and calcium carbonate 

 gypsum (calcium sulphate) is one of the salts formed. Aside from the 

 effect of lime in the role of an antagonistic agent, which will be discussed 

 later, one would predict from these results that an application of gypsum 

 would have little or no effect in overcoming black alkali that is being 

 formed by the action of sodium sulphate or mixtures of alkali containing 

 sodium sulphate upon lime. Furthermore, as many irrigation waters 

 already contain gypsum in appreciable amounts, little or no beneficial 

 effect may be expected from an application of gypsum to soils irrigated 

 with such waters. 



EFFECT OF SOLUBLE LIME SALTS UPON THE FORMATION OF SODIUM 



BICARBONATE 



As has been pointed out before, equilibrium must not necessarily be 

 reached in any of these reactions before the resulting components are 



^ 3000\ 

 f c'SOO 



M /500 

 \ 



.0: /OOO ■ 



b soo- 



^ O -5 /.O /.5 2.0 2'.S 3.0 35 4.0 <>.£ S.O S.5 6.0 6^ 70 7^ &0 



Fig. 13.— Graphs showing the efiect of soluble calcium salts upon the formation of sodium bicarbonate. 



carried away by drainage or the capillary action of the water. However, 

 in case the soluble lime remained in the place where it was formed, the 

 reaction would, of course, grow less with the increasing concentration of 

 lime. In order to determine the effect of these soluble lime salts on the 

 formation of sodium bicarbonate, solutions containing graduated amounts 

 of calcium nitrate in 20 per cent solutions of sodium nitrate, and gradu- 

 ated amounts of calcium chlorid in 10 per cent solutions of sodium 

 chlorid were prepared and brought to equilibrium by bubbling carbon- 

 dioxid gas through them. These results are shown in Tables XXIII and 

 XXIV and in figure 13. 



