550 



Journal of Agricultural Research 



Vol. X. No. II 



Table X. — Reaction between sodium sulphate and calcitim carbonate in 0.21 per cent 

 solutions of calcium sulphate 



In the case of all three salts, at some concentration there is an appre- 

 ciable formation of sodium carbonate, although gypsum is present in an 

 amount sufficient to saturate distilled water. This is more pronounced 

 with sodium sulphate than with the other salts. 



LIMITS OF THE FORMATION OF SODIUM CARBONATE IN PRESENCE 

 OF SOLUBLE AND INSOLUBLE SALTS OF LIME 



In titrating out the sodium carbonate formed by the action of the 

 sodium salts on calcium carbonate it was noted that the color with 



phenolphthalein soon 

 began to reappear in 

 the solutions when cal- 

 cium carbonate was 

 present after the titra- 

 tion had been finished, 

 indicating the forma- 

 tion of more sodium 

 carbonate. Under field 

 conditions the sodium 

 carbonate formed 

 would tend to be neu- 

 tralized or "titrated 

 out" by reacting with 

 the organic matter or 

 silicates of the soil. 



Acetic acid, repre- 

 senting a weak organic 

 acid and one which 

 gives a very soluble 

 salt of lime, and oxalic 

 acid, another weak 

 acid which gives a very 

 insoluble salt of lime, 

 were taken in stan- 

 dard solutions and 

 used instead of sulphuric acid to titrate out the sodium carbonate formed 

 by the action of sodium nitrate and calcium carbonate. In a rough way 



O S /O /5 20 c-S 30 3S -^^ 'fS SO SS 60 



/=£■/? cr/vr Ae>/\/Oj 



Fig. 4. — Graphs showing the sodium carbonate formed by reaction of 

 calcium carbonate (solid phase present) with sodium nitrate. So- 

 dium carbonate titrated out with acetic acid, allowing equilibrium 

 to be estabhshed between successive titrations. Numbers refer to 

 titrations. Each graph represents the total sodium carbonate neu- 

 tralized up to and including that titration. 



