Sept. lo, 1917 



Formation of "Black Alkali" 



587 



manner. Suppose sodium chlorid is deposited on the surface in a crys- 

 talline form, and rain or irrigation water dissolves this and carries it 

 down in a fairl)^ concentrated form until the hardpan is reached. Here 

 the evaporation of the water may further increase the concentration of 

 the salt and the action upon the lime carbonate may take place in a 

 rather concentrated solution. The black alkali, together with the solu- 

 ble lime salt formed and the excess of the sodium chlorid is then, or 

 thereafter, brought to the surface by the capillary action of the water. 

 Here the sodium chlorid may again crystallize out upon the surface and 

 be ready for the next rain or irrigation to carry it down through the soil 

 for a further action upon the calcareous hardpan. This phenomenon 

 was strikingly brought out in the experiment, illustrated in Plate 62, C. 

 Two lantern chimneys were filled with pure quartz sand, and during the 



fTft-^O 



Fig. 26. — Graphs showinK the sap>onificaticm of ethyl acetate by sodium carbonate in the presence of sodium 



sulphate. 



filling a thin layer of calcium carbonate was introduced into each. In 

 No. I the bottom was stopped up and the layer of calcium carbonate 

 placed at the lower end of the column; in No. 2 the calcium carbonate 

 was placed about midway, and the bottom of the chimney closed with 

 a strip of hnen. No. i was then kept watered from the top with a 10 

 per cent solution of sodium sulphate, while No. 2 was placed in a large 

 evaporating dish, containing some of the same sodium-sulphate solution. 

 These chimneys illustrated two field conditions: One in which the calca- 

 reous hardpan is at the lower edge of the moisture plane, where under 

 field conditions it would exist, the water having to penetrate the full 

 depth of the soil to reach it; the other where the hardpan lies near the 

 surface, the water, entering below, has to pass through the layer in order 

 to reach the surface. 



After several days sodium carbonate appeared on the surface of both 

 chimneys of sand. In the case of No. i, the sodium sulphate penetrated 

 the sand until the calcium carbonate was reached, the reaction between 



