THE LIME CARBONATE PROBLEM 387 



tween carbon dioxide in the atmosphere and the calcium sulphate, calcium 

 carbonate, and calcium bicarbonate of water solutions in contact with it,* 

 makes it plain that : 



1. If the natural waters of the earth were supposed to contain only 

 lime salts — that is, the sulphate, carbonate, and bicarbonate in equilib- 

 rium with the carbon dioxide of the atmosphere^— and if the average par- 

 tial pressure of carbon dioxide in the atmosphere were the same as at 

 present (0.0003 atmosphere), by evaporation the gypsum would be pre- 

 cipitated with contamination of .9 per cent of calcium carbonate. If the 

 carbon dioxide were reduced to 1/10 the amount in the present atmos- 

 phere — a condition hardly conceivable — the gypsum would still be pre- 

 cipitated with contamination of calcium carbonate, though the amount 

 would be reduced to .3 per cent. If the carbon dioxide were increased to 

 10 times the amount in the present atmosphere, the calcium carbonate 

 contamination would increase to 2.85 per cent. 



3. The presence of other sulphates which might be found in sea-water 

 would increase the calcium carbonate contamination of the gypsum. 



3. An increase of temperature by decreasing the coefficient of absorp- 

 tion of carbon dioxide would jDossibly be a favorable factor in the forma- 

 tion of pure gypsum by evaporation of sea-water. Such increase in tem- 

 perature, however, would probably come with an increase in the amount 

 of carbon dioxide in the atmosphere, and, as has been noted, an increase 

 in the carbon dioxide content of the atmosphere means a rapid increase 

 in calcium carbonate contamination of the gypsum. 



4. The presence of very large amounts of sodium chloride (about 8 to 

 25 per cent) would have a tendency to reduce the calcium carbonate con- 

 tamination. 



Stieglitz calls attention to IJsiglio's work on mediterranean water, 

 where calcium sulphate began to be deposited when the water reached the 

 density of 1.13, which corresponds to a chloride content of 17 per cent. 

 This concentration, Stieglitz states,^ was reached in Cameron's experi- 

 ments for solution 7, from which, going to solution 8, gypsum would be 

 obtained with about .8 per cent of carbonate. 



5. "Even if tlie great mass of au excess of caloium carbonate in a solution 

 were deposited first in some other locality before tlae point of saturation for 

 gypsum were reached, the requirements for equilibrium would be such as to 

 hold carbonate in solution and to make the (juestion of the place of deposit of 

 the excess of carbonate in the (ii'st instance one of no moment." 



■'The tidal and other problems. Published by the Carnegie Institution of Washington, 

 1909. 



= The tidal and other problems. Carnegie In.stitution of Washington, I'.inO, p. 262. 



