1909] on Tantalum and its Industrial Applications. 595 



one of them has been heated in an atmosphere of nitrogen, the other 

 in hydrogen, and the third has not been interfered with. The 

 consequence is that the latter has retained its strength, while the 

 former have become brittle and useless. 



On heating tantalum in air, it shows first a yellow and then a 

 blue tint like steel, but when the heating is continued it burns to 

 pentoxide. 



The black powder and thin wires can even be lighted by applying 

 a match to them, as the experiment shows. 



Its melting-point, in vacuo, lies between 2250° C. and 2300° 

 Celsius, which makes it particularly suitable for electrodes in vacuum- 

 tubes, especially as it does not disintegrate — for example, Ta electrodes 

 are extensively used in Roentgen tubes —and its specific weight is 16 * 6. 



Turning now to the electrical qualities of tantalum, its specific 

 resistance was stated by Dr. von Bolton, in 1905, to be on the 

 average 0*165, with a temperature coefficient of 3 per cent, between 

 0° and 100° Celsius. 



Further experiments conducted by Dr. Pirani in the laboratory 

 of Siemens and Halske revealed the fact that wires of various thick- 

 nesses varied in their specific resistance from 0*173 to 0*188 ; but 

 after they had been heated to 1900° Celsius in a high vacuum for 

 from 100 to 200 hours, they all possessed the same specific resistance, 

 viz. ; 0*146, and their temperature coefficient between 0° and 100° 

 Celsius had risen to 0*33 per cent. 



As a temperature of the tantalum filament, when consuming 

 1*5 watt per candle-power, is about 1850° C, and its resistance about 

 six times its resistance at 100° C, the temperature coefficient between 

 100° and 1850° C. may be taken, on the average, as 0* 29 per cent. 



No doubt the difference between these results is caused by altera- 

 tions in the structure of the wires during their manufacture, and the 

 heating in vacuo served a similar purpose to the annealing of steel, so 

 that Dr. Pirani's results published in 1907 may be taken as standards. 



At present, the most important industrial application of tantalum 

 is its use for the filaments of incandescent lamps, which may be said 

 to date from July 1903, when Dr. Feuerlein had succeeded in pro- 

 ducing a tantalum wire one-twentieth of a milHmetre in diameter. 

 Of this wire he made a glow lamp with a filament 54 mm. long, using 

 a current of 9 volts * 58 amps., and giving a light of 3*5 candles 

 (Hefner), at the rate of 1 * 5 watt per candle power. 



A simple calculation shows that for a current of 110 volts, 660 mm. 

 of the same wire would be required giving at the same rate of con- 

 sumption of energy a light of 43 candles. 



In carbon lamps for 220 volts the length of filament is only 

 400 mm., and the filaments remain hard until they disintegrate. 

 Tantalum filaments, like other metallic filaments, soften, however, to 

 such a degree that they cannot be used in the same shape as carbon 

 filaments. 



