1909] on Tantalum and its Industrial Applications. 591 



in shortening its life, and destroying thereby its power of competing 

 with gas lighting. 



An improvement on this result was introduced by Prof. Nernst, 

 of Gottingen, who suggested, as the source of light, refractory earths, 

 similar in character to those used for gas mantles, which, however, 

 conduct electricity only when they are hot. 



Lamps constructed on Prof. Nernst's principle have, therefore, to 

 be fitted with contrivances for heating their filaments when starting, 

 which complicate the construction of the lamp. 



x\nother step forward was made by the invention of the osmium 

 lamp, which is produced in a somewhat similar manner to the carbon 

 lamp, by squirting a plastic mixture of metallic oxide and a reducing 

 agent into the shape of a filament, which is gradually heated in a 

 glass bulb by the passage of an electric current, while the bulb is 

 being exhausted by an air pump, or an equivalent device. 



As far as utilisation of energy goes, these lamps are a great im- 

 provement on carbon lamps, but their filaments are very brittle ; and 

 the total production of osmium per year is only about 8 kg. for the 

 whole world, of which 5 kg. are wanted for medical purposes. 



In January 1905 Dr. W. von Bolton, the head of the chemical 

 laboratory of the firm of Siemens and Halske, announced in a lecture 

 to the Elektrotechnische Verein of Berlin that he had succeeded in 

 producing pure tantalum, and his discourse was followed by Dr. 0. 

 Feuerlein, describing how tantalum had been utilised for filaments in 

 the lamp works of the firm. 



These discourses presented the result of long years of research 

 work, based on the general principle already alluded to, that that 

 filament would give the best economical results which could be 

 maintained for the longest time at the highest temperature. 



The number of substances capable of conducting electricity and 

 of sustaining such high temperatures is very limited, and platinum, 

 the most refractory of the well-known metals, had been tried and 

 found wanting. 



It became, therefore, necessary to start the research by devising 

 methods for producing the rare metals in a commercially possible 

 manner, and then try one after the other as filaments of incandescent 

 lamps. 



While working on these lines. Dr. von Bolton succeeded, in the 

 first instance, in producing a vanadium filament by heating a mixture 

 of vanadium pentoxide and paraffin to 1700° C, and thereby pro- 

 ducing sticks of vanadium trioxide, which in their turn were heated 

 by electric currents in a glass bulb exhausted by an air-pump, and so 

 converted into metallic filaments. 



As it was found that vanadium melts at about 1680° C, such 

 filaments were no improvement on carbon filaments ; and the next 

 substance to be investigated was niobium, which belongs to the same 

 group of elements, but has nearly double the atomic weight. 



