236 EQUILIBRIUM BETWEEN CARBON DIOXIDE OF ATMOSPHERE 



Considerations of this nature led the author in 1903/ in the course of a 

 conversation with Dr. T. C. Chamberlin on the remarkable freedom from 

 calcium carbonate of a deposit of gypsum,^ to suggest that possibly there 

 might be some connection between the purity of the gypsum and the carbon 

 dioxide content of the air at the period of the gypsum formation, since the 

 carbon dioxide in the atmosphere is one of the most important factors 

 influencing the solubility of calcium carbonate. 



Inasmuch as climatic conditions, according to recent theories enter- 

 tained quahfiedly by Dr. Chamberlin, are also dependent to a certain degree 

 on the carbon dioxide in the atmosphere, it seemed possible that a study 

 of the precipitation of calcium sulphate and calcium carbonate from the 

 point of view of the laws of equihbrium might lead to conclusions which 

 would be of some use as a further source of information relative to condi- 

 tions existing at a remote period. 



Partly on account of the possibility of obtaining results of some such 

 specific geological value for the work on the cHmates of the earth; chiefly, 

 however, in order to test the possibility of exploiting this method of investi- 

 gation for geological purposes, Dr. Chamberlin asked me to undertake, in 

 collaboration with himself, the work of making the necessary calculations 

 on the conditions of equihbrium determining the precipitation of calcium 

 sulphate and calcium carbonate.^ 



As is usual in these cases, it was decided to consider first the ideal case 

 of solutions containing only the two salts in question. But the work has 

 been extended to estimate proximately the influence of the presence of 

 other sulphates in the solutions in the proportions found in ocean waters of 

 the present day; and finally an attempt has been made to consider the 

 effect of concentrated salt (sodium chloride) solutions on the conditions 

 studied. The results obtained for the simpler case of equilibrium for dilute 

 solutions in the presence of sulphates and moderate amounts of sodium 

 chloride may, it is hoped, also prove useful in connection with present-day 

 problems on the calcium carbonate content of the oceans and of fresh waters. 



The study of the equilibrium conditions controlling the precipitation of 

 calcium carbonate and sulphate falls naturally into two parts — a study, on 

 the one hand, of their relative solubilities, and the consideration, on the 

 other hand, of the conditions of equihbrium for saturated solutions of cal- 

 cium carbonate, calcium bicarbonate, and carbonic acid in equihbrium with 

 an atmosphere of some given content of carbon dioxide, the latter being a 

 determining factor in the total solubiHty of carbonate. This second and 

 more complex part of the study will be taken up first. 



» Year Book No. 2, Carnegie Institution of Washington, p. 269. 



» The observation was made by Mr. F. A. Wilder in the course of an investigation for 

 a doctor's thesis submitted to Professor Cham.berlin. 



' Pressure of other work made it necessary to postpone the calculations to the year 1907 



