July 2-Sepi. 24, 191 7 



Illustrations XV 



Page 



Formation op "Black Alkali" (Sodium Carbonate) in Calcareous 



Soils 



Fig. I. Graphs of the sodium carbonate formed from reaction of calcium car- 

 bonate with sodium chlorid, sodium nitrate, or sodium sulphate . . . 544 



2. Graphs showing the depression of sodium carbonate formed by the 



reaction of calcium carbonate with sodium chlorid, sodium nitrate, 

 or sodium sulphate when a soluble calcium salt containing a common 

 anion is added 548 



3 . Graphs showing the effect of gypsum on the formation of sodium carbon- 



ate in the reaction of calcium carbonate with sodium chlorid, sodium 

 nitrate, or sodium sulphate 549 



4. Graphs showing tlie sodium carbonate formed by reaction of calcium 



carbonate (solid phase present) with sodium nitrate. Sodium 

 carbonate titrated out with acetic acid, allowing equilibrium to be 

 established between successive titrations. Numbers refer to titra- 

 tions. Each graph represents the total sodium carbonate neutralized 

 up to and including that titration 550 



5. Graphs showing the sodium carbonate formed b}^ reaction of calcium 



carbonate (solid phase present) with sodium nitrate. Sodium car- 

 bonate titrated out with oxalic acid, allowing equilibrium to be 

 established between successive titrations. Numbers refer to titra- 

 tions. Each graph represents the total sodium carbonate neutralized 

 up to and including that titration 551 



6. Graphs showing the sodium carbonate formed by reaction of calcium 



carbonate and sodium chlorid. Sodium carbonate titrated out with 

 hydrochloric acid, allowing equilibrium to be established between 

 successive titrations 552 



7. Gra.phs showing the sodium carbonate formed by reaction of calcium 



carbonate and sodium sulphate. Sodium carbonate titrated out 

 with sulphuric acid, allowing equilibrium to be established between 

 successive titrations 553 



8. Graph showing the same system as in hgure 5, but titrated with carbon- 



dioxid solution 555 



9. Graph showing the same system as in figure 6, but titrated witli carbon- 



dioxid solution 555 



10. Graph showing the same system as in figure 7, but titrated with carbon- 



dioxid solution 556 



11. Graphs showing the concentration of sodium bicarbonate in the sys- 



tems discussed above when in equilibrium with carbon dioxid at 

 approximately atmospheric pressure 558 



12. Graph showing the same systems as in figure 11, with the addition of 



calcium sulphate in excess 559 



13 . Graphs showing the effect of soluble calcium salts upon the formation of 



sodium bicarbonate 561 



14. Graphs showing the effect of sodium nitrate on the solubility of calcium 



in soil 563 



1 5 . Graphs showing the effect of sodium chlorid on the solubility of calcium 



in soil 563 



16. Graphs showing the effect of sodium sulphate on the solubility of cal- 



cium in soil 564 



1 7 . Graphs showing the effect of mixtures of sodium chlorid and sodium sul- 



phate on the solubility of calcium in soil 5^4 



