Sept. 10, 19x7 



Formation of ''Black Alkali'* 



547 



EFFECT OF SOLUBLE LIME SALTS UPON THE FORMATION OF SODIUM 



CARBONATE 



The quantity of sodium carbonate formed in the reaction of calcium 

 carbonate with sodium sulphate is relatively large in comparison with 

 that formed with sodium nitrate or sodium chlorid. It was suggested that 

 this might be due to the fact that in the reaction with sodium nitrate 

 and sodium chlorid very soluble salts of lime, calcium nitrate, and 

 calcium chlorid are formed, while with sodium sulphate a relatively 

 slightly soluble salt, gypsum, is formed. This has a practical significance 

 from the fact, as first advised by Dr. Hilgard, that the application of 

 gypsum will improve soils containing too much black alkali. This is 

 simply a reversal of the reaction considered above, as follows: Na2C03+ 

 CQ.S,O^T±^a^SO^ + CaCOg. 



The following tables and curves will show the concentration of the 

 soluble salts of lime that are required to stop the reaction at its maximum. 



Table V. — Reaction between 20 per cent solutions of sodium nitrate and calcium carbonate 

 in the presence of calcium nitrate 



Table VI. — Reaction between 10 per cent solutions of sodium chlorid and calcium 

 carbonate in the presence of calcium chlorid 



Table VII. — Reaction between 20 per cent solutions of sodium sulphate and calcium 

 carbonate in the presence of calcium sulphate 



