51 



April 10. 



Rev, B. LLOYD, D. D., Provost T. C. D., President, 

 in the Chair. 



Rev. Charles William Wall, D. D., F. T. C. D., Robert 

 William Smith, M. D., and William Armstrong, Esq., were 

 elected Members of the Academy, 



A paper was read " On a new variety of Alumn," by 

 James Apjohn, M. D., M. R. I. A., Professor of Chemistry 

 in the Royal College of Surgeons, Ireland. 



This paper commenced with a brief description of the 

 physical characters and chemical properties of the mineral 

 in question, which was found about 600 miles to the north 

 of the Cape of Good Hope, near Algoa Bay, where it occurs 

 in strata whose aggregate thickness is about twenty feet. 

 The specimen described is composed of transparent threads 

 or fibres, exhibiting a beautiful silky lustre, and in appear- 

 ance closely resembling satin-spar or the finer forms of ami- 

 anthus. In taste, solubility in water, and other properties, it 

 corresponded with ordinary alumn. It was also easily shown 

 to contain sulphuric acid and alumina, but in addition it 

 contained a base which, though precipitated like alumina 

 by potash, was not redissolved by an excess of the alkali. 

 This, upon examination, turned out to be protoxide of man- 

 ganese. There was no alkali, but about one per cent, of 

 sulphate of magnesia. 



In the first attempt at effecting the analysis of the mine- 

 ral it was found that alumen and protoxide of manganese 

 could not be separated perfectly by potash, as some of the 

 oxide was taken up by the alkali, while a considerable quan- 

 tity of alumen was left behind with the oxide. The author 

 explained a method of overcoming this difficulty, the parti* 

 culars of which are given in detail in the paper. The fol- 



e2 



