FOREIGN CORRESPONDENCE. 



397 



of the sulphur, and a small proportion of the carbon. This is ex- 

 empli ded in the composition of sea- water, for the salts it coutains it 

 has obtained whilst hltering through the strata of the earth. 



It was the action of these solnble salts upon the three categories of 

 sedimentary strata, that the author deemed it necessary to investigate. 



The following results have been obtained : — 



Limestones. — Alany experimentalists,^ acting upon ideas enunciated 

 by Leop. von Buch, that dolomite resulted from the substitution of one 

 equivalent of magnesia for one equivalent of lime, in limestones, have 

 obtained a mixture containing magnesia and lime, in the proportion of 

 dolomite, by heating to 200° (centigrade), and at a pressure of 15 

 atmospheres, carbonate of lime with sulphate of magnesia or chloride of 

 magnesium. IT. Ch. Deville has shown that the same re-action can take 

 place at 100^ (centigrade) — boiling- water point — and at- the ordinary 

 pressure of the atmosphere. He steeped a fragment of chalk in a solution 

 of chloride of magnesium, until it had absorbed as much as possible of 

 the liquid, and then heated it to 100^ in a crucible. He observed what 

 Dulong, when studying the action of soluble salts upon insoluble ones, 

 had remarked before, namely, that the re-action takes place, but is very 

 limited. Thus, by one operation, six or seven per cent, of lime only is 

 replaced by magnesia. But, if the piece of chalk be washed so as to 

 eliminate the chloride of calcium formed, steeped again into the chloride 

 of magnesium, and a second operation effected, more lime is replaced 

 by magnesia ; and, after the eighth experiment, the two bases are in 

 the proportion 1 : 2 or 1 •: To, that is, as they are found in dolomite. 



What takes place in these experiments may be clearly seen by the 

 following formula : — 



Insoluble. Soluble. Insoluble. Soluble. 



2 Ca C + Mg CI = (Ca C + Mg C) + Ca CI 



2 equiv. of Carb. + Chloride of = Dolomite. + Chloride of 

 Lime Magnesium. Calcium. 



Fragments of coral, &c,, were treated in the same manner, and 

 transformed into dolomite (after a succession of imbibitions with chloride 

 of magnesium and calcination to 100*^ C), without losing their organic 

 structure or their external appearance. These experiments call to mind 



* Haidinger, de Morlot, Mariguac, Durocher, &c. — T. L. Pi 



