Following closely upon the development of the tantalum lamp came the tungsten lamp. Tungsten possesses a very high melting point and an indirect method is employed in forming filaments for incandescent lamps. There are several of these methods in use. In one method a fine carbon filament is flashed in an atmosphere of tungsten oxychloride mixed with just the proper proportion of hydrogen, in which case the filament gradually changes to one of tungsten. A second method consists of the use of powdered tungsten and some binding material, sometimes organic and in other cases metallic. The powdered tungsten is mixed with the binding material, the paste squirted into filaments, and the binding material is then expelled, usually by the aid of heat. Another method of manufacture consists of securing tungsten in colloidal form, squirting it into filaments, and then changing them to the metallic form by passing electric current through the filaments.

Fit. 14. Distribution Curves for Tantalum Lamp. No. 1, 40 Watts; No. 2, 80 Watts.

Fit. 14. Distribution Curves for Tantalum Lamp. No. 1, 40 Watts; No. 2, 80 Watts.

The tungsten lamp has the highest efficiency of an of the oommercial forms of metallic filament lamps now in use, about 1.25 watts per candle-power when operated so as to give a normal life, and lamps for 110-volt service and consuming but 40watts have recently been put on the market. A 25-watt lamp for this same voltage appears to be a possibility. The units introduced at first were of high candlepower because of the difficulty of manufacturing the slender filaments required for the low candle-power lamps.

The advantages of these metals, tantalum and tungsten, for incandescent lamps are in the improved efficiency of the lamps and the good quality of the light, white or nearly white in both cases. In either case the change in candle-power with change in voltage is less than the corresponding change in an ordinary carbon lamp. The disadvantage lies in the fact that the filaments must be made long and slender, and hence are fragile, for low candle-power units to be used on commercial voltages. In some cases tungsten lamps are constructed for lower voltages and are used on commercial circuits through the agency of small step-down transformers. Improvements in the process of manufacture of filaments and of the method of their support have resulted in the construction of 110-volt lamps for candle-powers lower than was once thought possible. Figs. 15 and 16 show the appearance of the tungsten lamp, and Figs. 17 and 18 give some typical distribution curves. Table V and VI give data on this lamp as it is manufactured at present. One very considerable application

Fig. 15. Multiple Tungsten Lamp.

Fig. 15. Multiple Tungsten Lamp.

Fig. 1 6. Series Tungsten Lamp.

Fig. 1 6. Series Tungsten Lamp.

Fig. 17. C. P. Distribution Curves of 100 watt Gen. Elec. Tungsten

Fig. 17. C. P. Distribution Curves of 100-watt Gen. Elec. Tungsten.

Incandescent Units with B-3, C-3, and D-3 Holophanes of the tungsten lamp is to incandescent street lighting on series circuits, in which case the lamp may be made for a low voltage across its terminals and the filament may be made comparatively short and

FIG. 18. Candle Power Distribution Given with 40 c. p.

FIG. 18. Candle-Power Distribution Given with 40 c. p.

Gen. Elec. Tungsten Series Lamp and Radial Wave Reflector heavy. The tungsten lamp is also being introduced as a low voltage battery lamp.

The Just lamp, the Z lamp, the Osram lamp, the Zircon-Wolfram lamp, the Osmin lamp, etc., are all tungsten lamps, the filaments being prepared by some of the general methods already described or modifications of them.

Table V. Tungsten Lamps

MULTIPLE

Watts

Volts

Candle-Power

Watts

PER

C. P.

Tip Candle-Power

Spherical

Reduction

Factor

40

100

32

1.25

5

76.3

60

125

40

1.25

5.6

76.3

Table VI. Tungsten Lamps

SERIES

Amperes

VOLTS

Candle-Power

Watts per C. P.

4

13.5

40

1.35

20.25

60

5.5

9.8

40

1.35

14.7

60

6.6

8.2

40

1.35

12.3

60

7.5

7.2

40

1 35

10.8

60