56 GEOLOGICAL MEMOIRS. 



rating nearly to dryness a mixture of carbonated lime-water and sea- 

 water at a temperature of 90° Centig. and washing the precipitate, 

 a proportion of 



Carbonate of lime. ..... 98-51 T loo-oo^ib yto- 



Carbonate 01 magnesia. . 1'49 j r i? ,, 



This explains why the roe-stones contain nearly pure carbonate of 

 lime, for the chemical action must in their formation have been ex- 

 tended over a long time ; and hence it follows that this carbonated 

 lime-water at the boiling-point of water can only deposit a quantity 

 of magnesia below 1 3 per cent, of the whole compound precipitate : 

 this is my reason for fixing the limit of the *' dolomitic limestone." 



The next series of experiments relate to the action of the carbo- 

 nated aqueous solution of lime and soda [natron] on sea-water. This 

 solution was prepared by adding as much carbonate of soda to the usual 

 carbonated lime-water as it could bear without becoming clouded. 



In three experiments I obtained, under different degrees of heat be- 

 tween 50° and 100° C, 13-10, 14-85, 27-93 per cent, of carbonate of 

 magnesia. In these also there occurred the same uncertainty of re- 

 sults as in the experiments with the pure carbonated lime-water, 

 evidently occasioned by certain conditions as yet unrecognized. This 

 much, however, results from these experiments, that the carbonated 

 natron-lime-water deposits a greater proportion of the carbonate of 

 magnesia than the pure carbonated lime-water ; and whilst the latter 

 precipitates " dolomitic limestone " from sea-water, the former sepa- 

 rates "dolomite." 



The third series of experiments will serve to determine how some 

 of the best-known mineral springs will act upon sea-water when 

 brought into chemical relation with it. The decompositions were 

 made with the aid of boiling. 



Selters-dolomite was composed of — 



Carbonate of lime 86*55 



Carbonate of magnesia . . 13*45 



Pyrmont-dolomite, calculated after the double iron-salt proportion 

 was separated from the carbonated salts — 



Carbonate of lime 84*38 "1 



Carbonate of magnesia . . 5*12 > 100*00 

 Iron 10*50 J 



Wildung- dolomitic limestone is composed of 



Carbonate of lime 92*12 



Carbonate of magnesia . 



I have never obtained in my experiments dolomites that were as 

 rich in magnesia as they frequently occur in nature ; but I also freely 

 acknowledge that my experiments are very imperfect imitations of 

 nature ; and with regard to the temperature, it plainly results from 

 the theory, that the springs that now issue out with a heat of 1 00° 

 Centig. would have a higher temperature if the pressure of the air were 

 stronger, or if they came out under considerable pressure of water. 



I 100*00 



%ll} 100-00 



