Vol. 56.] OF MINEKALS CONTAINING KARE ELEMENTS. 529 



«ome into the possession of Thomas Allan, the Scottish mineralogist, 

 after whom the cerium-bearing mineral all an it e (which also 

 •occurs abundantly in Sweden and Norway) has been named. Erom 

 Scotland Gieseeke repaired to Dublin, where he became Professor of 

 Mineralogy to the Eoyal Dublin Society ; he was subsequently 

 knighted, and a medal was struck in his memory. 



Gieseeke's long stay and extensive travels with the Eskimaux in 

 Greenland produced important results from a mineralogical point of 

 view ; he discovered a great number of interesting localities rich in 

 minerals new to science. 



During the latter half of the nineteenth century several new, 

 unexpectedly rich finds of minerals have also been made in these 

 distant regions: thus, in 1853 and 1854 by Director H. Rink; 

 in 1870 by the Swedish Expedition to Greenland ; in 1876 by 

 Prof. K. J. V. Steen strap as a member of a Danish expedition to 

 Greenland ; and in 1897 by Dr. G. Elink. 



One of the minerals collected by Gieseeke was described under 

 the name of fergusonite in the Transactions of the Royal Society 

 of Edinburgh for 1826 by Haidinger. The first analysis of the 

 mineral was made two years later in the laboratory of Berzelius by 

 Victor Hartvall, Professor of Chemistry at the University of Hel- 

 singfors. Eergusonite attracted the attention of specialists on 

 account of its composition (it consists of gadolinite-earths combined 

 with tantalic and niobic acids) and certain peculiarities in its 

 crystalline form. But it remained an extremely rare mineral, 

 represented even in rich collections only by small fragments of 

 crystals, until I found, on examining the different ' varieties ' of 

 yttrotantalite from Ytterby, that one of them consisted of true 

 fergusonite, with the same composition and unusual crystalline form 

 as the mineral from Greenland. Moreover fergusonite had already 

 been found in 1855 in Norway, but the Norwegian fergusonite had 

 been described by David Eorbes and Tellef Dahll as new minerals 

 under the names of tyrite and bragite. During the later years 

 of the nineteenth century the same mineral has also been found at 

 several localities in the United States, and has been obtained in 

 fairly large quantity from Ytterby, as well as from various new 

 Norwegian localities. 



Fergusonite has lately become of special interest from a chemical 

 point of view, through the discovery that it contains a considerable 

 amount of inert gases. "When heated to 500° the mineral suddenly 

 begins to ignite, and yields, according to Prof. W. Ramsay, 

 1*43 cubic centimetres of inert gases per gramme of the mineral. 

 Erom this feebly ignited mineral 1-215 cubic centimetres of gas 

 could further be driven off by fusion with potassium-bisulphate. 

 About two-thirds of this gas, corresponding, at normal temperature 

 and normal pressure, to about 10 times the volume of the mineral, 

 •consists of helium. Thus fergusonite affords one of the richest 

 materials hitherto known for obtaining this mysterious gas (or 

 mixture of gases) which on our planet seems to be almost exclusively 

 •confined to minerals containing rare earths; and just as the earth 



