714 Proceedings of the Royal Irish Academy. 



amount of magnesia in them — dolomites being almost -unassailable. 

 Experiments 4 and 5 will show how well this is borne out. 



JSxp. 3. — As the limestone used in the last was hardly diminished 

 at all, it was again covered with distilled water, and carbonic acid 

 passed in. Care was taken to keep the solution just slightly acid, and 

 to avoid the error of Experiment 2. The action was continued for 20 

 days. The solution was then filtered oil, evaporated, and examined as 

 before, with the following result : — 



Carbonate of lime, .... 0-55 grains. 

 ,, magnesia, . . . 0'07 ,, 



,, iron, ..... a trace. 



Total dissolved, . . 0-62 



This experiment bears out the second very well, as to the total 

 qiiantity of substance dissolved, the time occupied being half of that, 

 and the total dissolved about half also. The proportion of magnesia is 

 less, however, no doubt owing to the precaution of using a weak solu- 

 tion of acid. The proportion calculated as before would give — 



Carbonate of lime, 68"21 



,, magnesia, . . . 9-04 



This agrees almost exactly with the proportions determined in 

 Experiment 1. 



1^0. II. — Limestonefrom the breccia of the roof of the Shandon Cave, 

 Dungarvan, Co. Waterford. A bluish-grey fossiliferous limestone, 

 apparently not very magnesian. It turns out, however, to contain 

 a rather large proportion of carbonate of magnesia. 



AXALYSIS. 



79-89 

 12-71 

 trace. 



Carbonate of lime, 



,, magnesia 



,, iron, . 



Peroxide of iron, . 

 Alumina, .... 

 Silica and insoluble residue, . 3-40 



J 4-08 



100-00 



JExp.A. — 187 grains of the limestone, broken in small pieces as 

 "before, were placed in a large jar with distilled water,* and carbonic 



* It should be noted that in all the experiments except No. 1 , the same quan- 

 tity of water was used, viz., about 20 oz. ; care being taken to sujjply loss l)y 

 ■evaporation. 



