108 CHEMICAL EQUILIBRIUM AND ANTAGONISM 



the insolubility of calcium carbonate. The mass law 

 states that at a given temperature 



(NaCl) 2 (CaC0 3 ) 



(Na 2 C0 3 )(CaCl 2 ) 



= a constant, 



where each one of the factors of the equation represents 

 the concentration in moles of that constituent in unit 

 volume. Though the factor (CaCOs) is very small it is 

 not zero and accordingly if water containing a large amount 

 of sodium chloride were passed over limestone there would 

 be a tendency for calcium carbonate to be changed into 

 sodium carbonate and calcium chloride, in order that this 

 equation might be fulfilled. 



This latter condition has been found to exist in certain 

 parts of Egypt where the soil contained excessive quantities 

 of sodium chloride and also contained calcium carbonate. 

 Instead of the reaction being Na 2 C0 3 + CaCl = 2 NaCl 

 + CaCOs, as is generally the case where these substances 

 are brought in contact with each other in somewhat equal 

 molecular concentrations, the reverse reaction took place, 

 forming black alkali and calcium chloride. As seen in 

 the above table of solubilities, calcium chloride is very 

 soluble and might easily be washed from the soil so that 

 the above reaction might under certain conditions result 

 in the formation of considerable black alkali. In like 

 manner, other apparently stable salts might, by changes 

 in molecular concentrations, react to form new substances 

 not possible under ordinary conditions, and in case one or 

 both of the end products were taken from the active mass, 

 there might be a profound change in the composition of 

 the chemical compounds. 



California experiments (4) show that up to a strength 

 of about 4000 parts per million of sodium sulphate, this 



