546 



Journal of Agricultural Research 



\o\. X, No. n 



Table III. — Reaction between sodium sulphate and calcium, carbonate 



Table IV. — Reaction between mixtures of equal parts of sodium, chlorid and sodium 

 sulphate and calcium, carbonate 



In the reaction NaN03+CaC03<=Na2C03 + Ca(N03)2, at a maximum 

 of about 20 per cent of sodium nitrate there is a possibility of a formation 

 of about 58 parts per million of sodium carbonate. 



In the reaction 2NaCl + CaC03<=^Na2C03 + CaCl2, at a maximum con- 

 centration of about ID per cent of sodium chlorid there is a possibility 

 of a formation of about 40 parts per million of sodium carbonate. 



In the reaction Na2S04 + CaC03^Na2C03 + CaS04, at the saturation 

 point of sodium, sulphate there is a possibihty of the formation of about 

 122 parts per million of sodium carbonate under the conditions of this 

 experiment. 



The reactions just described are what might be termed the reverse 

 reactions of those commonly considered when these salts are brought 

 together. With sodium chlorid and calcium carbonate, for example, 

 the reaction might be written CaCl2+Na2C03^CaC03+2NaCl; or cal- 

 cium, chlorid and sodium carbonate in equilibrium with calcium carbonate 

 and sodium chlorid. No matter which combination of salts is used, the 

 resulting system will be exactly the same, and in the reaction last 

 described there would still be about 40 parts per million of sodium 

 carbonate left after the reaction had run to an end. 



The drop in the curves, when sodium nitrate and sodiumi chlorid are 

 used, as the saturation point is approached, is noticeable. This drop 

 will be seen in all the cur^^es outlined in this paper wherever a reaction 

 takes place between calcium carbonate and sodium nitrate or sodium 

 chlorid. This is not the case with sodiu.m sulphate. The curve with 

 this salt rises uniformly until the saturation point is reached. This fact 

 will be explained later. 



