Haudmax — On the Carhoniferons Dolomites of Ireland. 709 



to subjected to the action of carbonated •water, assuming this to be 

 capable of remoying a greater quantity of carbonate of lime than of 

 carbonate of magnesia — m proportion to tJw.t in tlte roch — it is clear 

 that in the 'process of time we should have the percentage of mag- 

 nesia becoming greater and greater, until at last the rock approached 

 in chemical composition to a time dolomite. Horeover, the removal 

 of carbonate of lime Tvould give rise to a cayernous or porous con- 

 dition of the rock, and the calcareous water trickKng over the sides or 

 into these cavities Tvould result in a deposit of crystals of more or less 

 pure carbonate of lime therein. Every one who has paid any attention 

 to this subject is, no doubt, aware that the above are characteristics 

 of dolomite limestone. 



Upon the above assumption, which I have now good reason to 

 believe a certainty, I based a number of experiments with the view to 

 ascertain whether, when placed under conditions as near as possible 

 to those obtaining in nature, limestone does not yield more lime than 

 magnesia, when submitted to the action of carbonic acid in water. 



At the time I had not Bisehof's book at hand, and all the statements 

 I had seen gave just the opposite opinion. I was subsequently much 

 pleased to find that Bisehof's two experiments'^-' are confirmatory of my 

 results, and they being unknown to me then could have had no bias- 

 ing effect. 



It is without exception received, I believe, that carbonate of mag- 

 nesia is much more soluble than carbonate of lime ; but the few expe- 

 riments I have made on this point do not appear to show any great 

 difference ; and I have been led to imagine, therefore, that its be- 

 haviour in the presence of ammonia salts may have been taken by some 

 to represent its character under other circumstances. In the process 

 of chemical analysis, when it is desired to separate magnesia from 

 lime, a little chloride of ammonia is added to the solution, and an 

 alkaline carbonate then precipitates the lime with just a trace of mag- 

 nesia. If, however, ammonia is not previously added, both salts are 

 almost instantly precipitated by carbonate of soda. 



But, even admitting that carbonate of magnesia is per se a trifle 

 more soluble than carbonate of lime, it is certain that, when both are 

 mingled together in a limestone rock, just the reverse takes place when 

 they are subjected to the action of carbonated water. My experi- 

 ments will show this. Before proceeding to refer to them, however, I 

 should like to mention the results obtained by previous experimenters. 



Professors W. B. and K. E. Eogers, at the lleeting of the British 

 Association at Birmingham, in the year 1849, read a paper on some 

 experiments as to the solvent power of carbonated water on various 

 minerals. f In the course of their experiments they were led to inves- 



* See post. 



t " On the Decomposition and Partial Sohition of Minerals, Eocks, &c., by pure 

 ■vratcr, and -water charged Avith Carbonic Acid." By Prof. "W. B. Rogers, and 

 Prof. R. E. Rogers. Rep. Brit. Assoc. 1819 ; Trans. cJf Ser-tions, p. 40. 



