746 FRANK A. WILDER 



that a maximum solubility for calcium carbonate was reached in 

 a solution holding 50 grams of sodium chloride per liter, when 

 its solubility was 2.36 times greater than in water without sodium 

 chloride, but in equilibrium with air. In view of these experi- 

 ments, which were conducted with great care, the experiments 

 of Thoulet and the conclusions based on them must be ques- 

 tioned. 



It is possible also to assume that chemical reactions took 

 place between the salts in solution, which resulted in the elimi- 

 nation of this lime carbonate, by converting it either into gypsum 

 or into a salt that is more soluble than gypsum, thus keeping it 

 in solution until after the gypsum was deposited. It is well 

 known that reactions between various salts contained in sea water 

 may causes divergence from the series which results from evapo- 

 ration alone. According to Usiglio, sea water deposits limestone 

 abundantly when the density reaches 1.0506, and again at 1.1304. 

 The last deposit he ascribes to the decomposition of sodium 

 carbonate and gypsum with the formation of sodium sulphate 

 and calcium carbonate.^ Oschenius holds that sudden and well- 

 marked deposits of gypsum may be caused by the addition of 

 sodium or calcium chloride. 



The solubility of gypsum in a sodium-chloride solution 

 increases with the strength of the solution, as shown in the fol- 

 lowing table by Cameron :^ 



NaCl AND CaS04 in Water at 150° C. 



Grams NaCI per Liter Grains CaSOi per Liter 



0.6 2.3 



I.I 2.5 



5.1 3-1 



10.6 3.7 



31. I 4.8 



51.4 5.6 



139-9 7.4 



So when the solution contains 140 grams of the NaCl per liter, 

 the solubility of CaSO^ is more than three times as great as in 

 water without sodium chloride. In solutions containing less than 



' Hubbard, Geological Survey of Michigan, Vol. V, Part II, pp. 1-33. 

 ^Journal of Physical Chemistry, Vol. V, No. 8, p. 559. 



