592 Mr. Alexander Siemens [April 23, 



Treated in a similar manner, the niobium filament gave some- 

 what better resiilts, but still its melting-point, estimated at 1950° C, 

 was too low for practical purposes. 



In this connection it should not be forgotten that, at a tem- 

 perature considerably below their melting-point, all these metals 

 begin either to soften or to disintegrate, so that their " working " 

 temperature is not identical with their melting temperature. 



Turning his attention to tantalum, which has an atomic weight 

 of 181, Dr. von Bolton experimented with the black metallic powder 

 produced by the method of Berzelius and Rose, and found that it 

 could be rolled into a fairly coherent mass in the form of ribbons. 



Alternative experiments, conducted on the lines by which vana- 

 dium and niobium had been obtained, resulted in the production of 

 pure tantalum in the form of a metallic button, which was found to 

 be tough and malleable hke steel. 



These and other qualities convinced Dr. von Bolton that nobody 

 before him had handled pure tantalum, although Berzelius had first 

 obtained the metal by a chemical process in 1824, and later Moissan 

 succeeded, in 1902, in producing it in his electric furnace. 



The latter describes tantalum as a hard brittle metal of the 

 specific gravity of 12*8 and a non-conductor of electricity, but he 

 adds that the substance obtained by him contained about a half per 

 cent, of carbon. 



Considering the high atomic weight of tantalum, this admixture 

 of carbon evidently exercises a great influence on the physical 

 qualities of tantalum, and explains the differences between the 

 observations of Dr. von Bolton and those of his predecessors. 



In nature ores containing tantalum are found in many places, 

 principally in Scandinavia, North America, South-west Africa, and 

 Western AustraUa. 



A specimen of columbite from South Dakota and another of 

 tantalite from Western Australia are exhibited. 



The columbite contains from 10 to 40 per cent, of tantalum 

 pentoxide (Ta205), and a good deal of niobium combined with iron 

 and manganese in various proportions. 



As the separation of tantalum and niobium is somewhat trouble- 

 some, it is preferable to utilise the tantalite, which consists almost 

 entirely of iron and manganese combined with tantalum pentoxide. 



From these ores tantalum is separated in the form of a fluoride 

 in combination with potassium (KgTa Fl^), and subsequently reduced 

 by metallic potassium to the black powder already mentioned, which, 

 however, still contains some oxide and some hydrogen. 



In order further to purify the product, the powder is pressed into 

 the form of small cyhnders (one of which is on the table), which are 

 melted in a vacuum by an electric current under certain precautions 

 into small buttons of pure tantalum such as are exhibited. 



Since the production of tantalum has been carried out on a com- 



