54 CHEMISTRY OF F.UIM PRACTICE 



TABLE III. EFFICIENCY OF SOAPS IN SOFTENING WATER 



(2) By treating the water with lye, sodium hydroxide, 

 CaH 2 (CO 3 ) 2 +2NaOH = CaCO 3 +Na 2 C0 3 +2H 2 0; 



(3) By treating with milk of lime, 



CaH 2 (CO 3 ) 2 +Ca(OH) 2 = 2CaCO 3 +2H 2 0. 



Permanent hardness is removed by treating the water 

 with sodium carbonate. The following equation may repre- 

 sent the reaction: 



CaSO 4 +Na 2 CO 3 = CaCO 3 +Na 2 SO 4 . 



The calcium carbonate in all these cases, being insoluble, 

 will be precipitated from the water, leaving in the water 

 sodium salts, which are not particularly harmful. 



Magnesium and iron salts react similarly to the cal- 



