712 Proceedings of the Royal Irish Academy. 



nearly as possible akin to that which goes on in nature, that more- 

 carbonate of lime is dissolved than carbonate of magnesia by a weakly 

 carbonated solution, it avouM go far towards solving the question, as. 

 to the formation of some dolomites. 



The process I adopted was very simple. A limestone was selected 

 which contained a fair percentage of magnesia, it was analysed, and 

 the proportions noted. A portion of the rock was then broken up into 

 small fragments, somewhat less than half-an-inch across. These were 

 placed in a jar open to the atmosphere, with distilled water, and car- 

 bonic acid was passed in. A piece of litmus paper was placed in the 

 jar, and the flow of gas was stopped as soon as this became reddened. 

 Whenever the paper showed any indication of returning to its original 

 tint, the solution was again saturated with the acid, and so on. In this 

 way an over saturation with acid (which might have had too energetic 

 an effect on the rock) was prevented, and the whole experiment brought 

 as near to nature as is possible in a laboratory, in having a mildly car- 

 bonated solution acting on surfaces of the rock, and not on minute 

 particles. 



With the process carried on in this manner, I found the action oi 

 the carbonic acid to be extremely slow, compared with the results ob- 

 tained from powdered rock by other experimenters, several days being 

 required to dissolve sufficient of the carbonates for estimation ; but in 

 every case the carbonate of lime was much in excess. Some of my 

 experiments were merely tentative, and are not worth recording ; but 

 I shall now mention the details of some of the more important ones. 



No. I. — Limestone from the interior of the Cave of Dunmore, Co. 

 Kilkenny. A light grey compact magncsian limestone. 



Analysis. 



Mean of two specimens. 



Carbonate of lime, 68-21 



Carbonate of magnesia, 24-00 



Peroxide of iron, . . / . on 



1 ' . \ . . . . 4-32 



,, alumina, \ 



Silica, 1-92 



Carbonate of iron, 0-90 



99-35 



It will be observed that this is a remarkably pure limestone, the- 

 amount of silicates, &c., being very small. The rock is evidently be- 

 coming dolomitic, for the limestone above and around the cave is not 

 by any means highly magnesian. 



Exp. 1. — A quantity of the limestone was broken up small. 110 

 grains were taken and placed in a jar with distilled water, and car- 

 bonic acid gas was passed in almost continuously for 72 hours. At 



