FORCHHAMMER ON THE FORMATION OF DOLOMITE. 55 



a small quantity of magnesia. There is deposited, on the other hand, 

 a mixture of carbonate of lime and carbonate of magnesia where the 

 spring-water has come into contact with the sea- water. We can 

 scarcely doubt that the carbonate of magnesia is precipitated by the 

 action of the water of these springs upon the magnesia- salts of the 

 sea-water. To confirm this theory, I have examined into the manner 

 in which mineral springs act upon sea-water. This examination is 

 not finished, and several points remain that are not yet satisfactorily 

 elucidated ; but the results already arrived at are quite sufficient to 

 show that the dolomitic limestones and dolomites are formed by this 

 mutual action of the springs and the sea-water. 



My first series of experiments relate to the mutual reaction of sea- 

 water and a solution of pure carbonate of lime in water charged with 

 carbonic acid, under different temperatures. The carbonate of lime 

 solution I call, for the sake of brevity, '' carbonated lime-water." 



1 . Carbonated lime-water mixed with sea-water was set in a frigo- 

 rific mixture until it was all frozen. After thawing, the deposit con- 

 sisted of — 



Carbonate of lime 92*45 1 i AA.nn 



Carbonate of magnesia .... 7" 55 J 



2. Sea-water mixed with carbonated lime-water stood for eight days 

 in a temperature of between 15° and 20° C. (determined by a ther- 

 mometrograph) ; the deposit was composed of — 



Carbonate of lime 97*81 1 iriA.An 



Carbonate of magnesia .... 2*19 

 3. The same mixture at 50° C. — 



} 



Carbonate of lime 96*22 1 i nn.nn 



Carbonate of magnesia .... 3*78 j 



*o" 



4. The same mixture at 87° C, in the vapour bath — 



Carbonate of lime 87*36 "1 inn.n/^ 



Carbonate of magnesia 12*64 j 



5. Sea-water was brought to ebullition, and carbonated lime-water 

 poured into it in a fine stream, so as not to be lost by the boiling : — 



Carbonate of lime 87*75 1 i nn rj^^ 



Carbonate of magnesia .... 12*25 J ^^^'^^ 



6. A similar experiment — 



Carbonate of lime 89*64 1 , nn-oo 



Carbonate of magnesia .... 10*36 J 



The above experiments are those of a series, in which the greatest 

 quantity of magnesia was precipitated under the given temperatures ; 

 but I obtained many less proportions, and these seem partially to be 

 dependent upon the variation of mutual action ; insomuch that the 

 longer the inter-action is continued, the less magnesia is proportion- 

 ally present in the precipitate. In like manner I obtained by evapo- 



