SKEATS: CHEMICAL COMPOSITION OF LIMESTONES. [2 
results of the earlier workers on the question of dolomite, and made 
many experiments himself. He showed : — 
(1) By dissolving mixtures of calcium and magnesium carbonates in 
water containing carbon dioxide, and then evaporating the solution at 
122° F., that under these conditions the calcium carbonate was com- 
pletely precipitated, while most of the magnesium carbonate remained 
in solution. 
Hence dolomite could not be formed under ordinary conditions by the 
evaporation of water containing the two carbonates in solution. 
(2) That the amount of carbon dioxide present in meteoric water 
sufficed for the production of a saturated solution of calcium carbonate. 
(3) That in limestones containing magnesium, water saturated with 
carbon dioxide dissolved out only the calcium carbonate. Even when 
11.5 % of magnesium carbonate was present only a trace of it was 
removed. 
He quoted also examples of limestones containing up to 68 % of 
magnesium carbonate. In these cases the carbonates were not chemi- 
cally combined, since dilute acetic acid dissolved out calcium carbonate 
alone. With true dolomite, the carbonates, when attacked, were dis- 
solved out in molecular proportions. 
The association of the dolomites of the Tyrol, with volcanic rocks rich 
in magnesia, led Von Buch? to suggest that the formation of dolomite 
was due to the eruption of volcanic rocks into a limestone, and that the 
change was brought about by the vapor of magnesium chloride. 
Haidinger? attributed its formation to the action of magnesium 
sulphate on a limestone, under great heat and pressure. 
Von Morlot * held a similar view to Haidinger, and by heating magne- 
sium sulphate and calcium carbonate in a sealed tube to a temperature 
of 392° F., succeeded in forming a double carbonate. 
Marignac * obtained a like result by substituting magnesium chloride 
for magnesium sulphate. 
All these writers assumed that the formation of dolomite is connected 
with the intrusion of igneous rocks. 
Later, Forchammer ® suggested the reaction of spring-water, contain- 
ing much calcium carbonate, with sea-water at a high temperature, as a 
possible cause of the precipitation of the double carbonate of calcium 
and magnesium. 
1 Ann. de Chim. et Phys., XXIIL., p. 296. 
2 Poggend Annal., LXXIV,, p. 591. 3 N. Jahrb. fiir Min., 1847, p. 862. 
4 N. Jahrb. fiir Min., 1849, p. 742. 5 Ann. de Chim. et de Phys. XXIII. 
