On the Potash and Soda Felspars of the Dublin Mountains. 365 



water, and after soaking for some time, the contents dug out, 

 gently crushed in a mortar, and washed by decantation. Two 

 or three globules of aluminium, tolerably large considering the 

 scale of the experiment, were obtained along with a great num- 

 ber of very small ones. The larger ones were melted together 

 under chloride of potassium. 



Some experiments made in iron crucibles were not attended 

 with the same results as those of Rose. No globules of any 

 considerable size remained in the melted fluorides; the metal 

 seemed to alloy with the sides of the crucibles, which acquired a 

 colour like zinc. It is possible that this difference may have 

 arisen from using a higher temperature than Rose, as these ex- 

 pei-iments were made in the furnace, not over the air-blowpipe. 



Porcelain and clay crucibles were also tried, but laid aside after 

 a few experiments owing to the action of the fluorides upon them, 

 which in most cases was sufficient to perforate them completely. 



These remarks, it is hoped, may tend to ch-aw the attciition of 

 experimenters still further to kryolite as a source of this interest- 

 ing metal; although the experiments which led to them were 

 carried only a short way towards the perfection which practice 

 would probably confer. 



Metalhirgical Laboratory, School of Mines, 

 October 26, 1855. 



L. On the Potash and Soda Felspars of the Dublin Mountains. 

 By Francis M. Jennings, M.R.I. A., F.G.S. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



THE paper of the Rev. Prof. Galbraith in the August Number 

 of your Journal, relative to the composition of the fel- 

 spars of the Dublin Mountains, shows that he entirely mistakes 

 the object of my remarks, which were to this effect : that when 

 an inference as to the composition of the felspar of a granite 

 mountain is to be made, the specimen analysed should par- 

 take as closely as possible of the general lithological character of 

 the mountain. Now the specimen selected by Mr. AV. Wilson of 

 the Geological Survey, and carefully analysed by Mr. Dugald 

 Campl;el), is very similar in its composition to those examined 

 by Prof. England and Mr. Foster (see Proc. Royal Irish Acad. 

 Feb. 28, 1H."j3), whilst the analyses of the Rev. Prof. Galbraith 

 are very different ; he, therefore, is not in a position to charge 

 others with want of care in the analyses, nor is he correct 

 in saying, that to estimate the quantities of potash or soda in 

 felspar it is necessary to determine the quantities of silica, &c. 



