62 Scientific Proceedings, Royal Dublin Society. 



Neglecting the influence of the small quantity of iolite present, 

 and also the influence of the chloritic mineral, this gives a percen- 

 tage composition — 



Beryl, . . . 54-4 



Orthoclase, . . 45-6 



2. It is evident from the figures previously given that the 

 specific heats will not enable a direct percentage estimation to be 

 made. Thus the specific heat of Glencullen beryl was found to be 

 0*2140 ; of the mixed crystal (the same used in investigation by 

 specific gravity), 0-2156 ; while the following results were obtained 

 for Grlencullen orthoclase : — 



(a) . . . 0-1982 

 (&) ... . 0-1976 



giving a mean of 0-1979. Hence, a specific heat lower, and not 

 one higher, than that of beryl was to be expected. In fact, calcu- 

 lating it in the percentages obtained above by specific gravity, the 

 specific heat of such a mixture would be about 0-207. It is re- 

 markable that the large percentage of water (T4) revealed in the 

 analysis of this specimen will just account for the discrepancy. 

 Beryl normally contains no water, and this orthoclase, by Gral- 

 braith's analyses, 0-58 per cent. only. Assuming this as high as 

 0*3 per cent, of the whole, an abnormal quantity of water, equal to 

 over one per cent., is present. Taking it as low as one per cent., 

 and re-calculating, the theoretical specific heat is found to be 

 0-2150. 



3. According to microscopical examination, orthoclase is the only 

 mineral present which is known to contain an appreciable amount 

 of potash. Analysis shows that there is 5-11 per cent, of K 3 in 

 the mixed mineral, the same specimen being used that had served 

 for the previous investigations. Now, as the result of Prof. 

 Galbraith's seven analyses, 1 the felspar of this granite contains 

 12-2 per cent, of potash. On these data we find orthoclase 42 per 

 cent. 



If, however, we calculate the percentage of beryl by the per- 

 centage of BeO given below, and by the result of Mallet's analysis 

 of Killiney beryl (he obtained 13'09 per cent of BeO — Dana), so 



1 Journal of the Geological Society of Ireland, yol. vi., p. 226, 



