Hardman. — On tJie Carhoiiiferous Dolomites of Ireland. 713 



the expiration of that time the solution was carefully filtered off and 

 examined. It contained both carbonate of lime and of magnesia, but 

 in extremely small quantity, viz. : — 



Carbonate of lime, .... 0-05 grains. 

 Carbonate of magnesia, . . . 0'007 ,, 



Calculated now according to the percentage of carbonate of lime 

 in the rock, i. e., 68-21, the above gives the respective proportions dis- 

 solved to be — 



Carbonate of lime, ...... 68-21 



,, magnesia, . . . 9-32 only, 



or less than half the proportion of carbonate of magnesia actually in 

 the rock. It is clear, therefore, that this operation, continued suffi- 

 ciently long, must result in a dolomite. 



£xp, 2. — About the same quantity of the Dunmore limestone was 

 taken — 110 grains, and placed in a jar with water as before. Carbonic 

 acid gas was then passed in, nearly continuously for 44 days. Tor 

 about a week or so of that time no gas was passed in, but for the most 

 part of this experiment the water was supersaturated with the acid, 

 the result of which will be presently seen. 



The liquid, having been carefully filtered off, evaporated to dryness, 

 and the residue examined yielded the following result : — 



Carbonate of lime, 1-04 grains. 



,, magnesia, . . . 0-306 ,, 

 ,, iron, a trace. 



Total dissolved, . . 1-346 



Calculating again according to the proportion of carbonate of lime 

 in the rock, we have — 



Carbonate of lime, 68-21 



,, magnesia, 20-06 



I attribute the high percentage of magnesia carbonate dissolved in 

 this instance to the supersaturated condition of the carbonic acid solu- 

 tion, which was allowed to become quite in excess of anythiug that 

 could occur in nature. ^Nevertheless, it is evident that the carbonate 

 of lime was the most rapidly dissolved in this case also. 



It seems remarkable also that so small a portion of the limestone 

 was dissolved after such long continued action. However, this was 

 confirmed in other experiments, and I apprehend it is due to the mag- 

 nesian character of this rock. It is certain that the action of small 

 quantities of carbonic acid on limestones is in an inverse ratio to the 



