254 Dr T. THOMSON'S Account of the 



or it consists of 



2 atoms bisilicate of alumina. 



1 atom tersilicate of lime, with some tersilicate of potash. 



3 atoms water. 



{Tjj ". 



Mr MITCHELL, at my request, tested the alkali for soda in the 

 following manner : The alkaline solution in muriatic acid was 

 mixed with an excess of muriate of platinum, and the mixture 

 was evaporated to dryness on the sand-bath, by a gentle heat. 

 The dry mass was digested in spirits, and the liquid, holding in 

 solution muriate of platinum, was evaporated to dryness in a pla- 

 tinum crucible, having been previously mixed with some sulphu- 

 ric acid. The dry mass was ignited to reduce the platinum to 

 the metallic state. The matter in the crucible was now digested 

 in water. This liquid being slowly evaporated to dryness, no 

 sulphate of soda appeared ; nothing indeed was found but a trace 

 of sulphate of lime, too small to admit of being weighed. Thus 

 it appears that Brewsterite contains no soda. 



7. Amianthus from Sardinia. 



The beautiful white amianthus from Sardinia, composed of 

 threads, which can be easily teazed from each other, and admit 

 of being spun, is well known to mineralogists. As it possesses 

 no marked characters, it is only by analysis that we can form an 

 opinion of the mineral species with which it is connected. I 

 therefore requested Mr RICHARD MITCHELL to analyse a spe- 

 cimen of this beautiful amianthus, for which I was indebted to 

 my friend CHARLES MACINTOSH, Esq. of Crossbasket. Its spe- 

 cific gravity was 1.551. 



