FOREIGN CORRESPONDENCE. 
397 
of the sulphur, and a small proportion of the carbon. This is ox- 
einpUtied in the compositioa of sea- water, for the salts it coutaias it 
has obtained whilst tilteriug through the strata of the earth. 
It was the action of these soluble salts upon the three categories of 
sedimentary strata, that the author deemed it necessary to investigate. 
The following results have been obtained : — 
Limestones. — Many 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. M. Oh. 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 oue operation, six or seven per ctnt. 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 elfected, 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. 
AVhat takes place in these experiments may be clearly seen by thd 
following forujula :■ — 
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 miud 
* Haidinger, de Morlot, Marignac, 'Durocher, &c. — T. L. P. 
