Lamp, Incandescent

a refractory conductor by the pa age of a current of electricity. It is distinguished from an arc lamp (which etymologically is also an incandescent lamp) by the absence of any break in the continuity of its refractory conductor. Many different forms and methods of construction have been tried, but now all have settled into approximately the same type. The incandescent lamp consists of a small gla bulb, called the lamp-chamber, which is exhausted of air and hermetically sealed. It contains a filament of carbon, bent into a loop of more or le simple shape. This shape prevents any tensile strain upon the loop and also approximates to the outline of a regular flame. IMG:8956969607833025625_321F212.jpg: Fig. 212. INCANDESCENT ELECTRIC LAMP. 322   STANDARD ELECTRICAL DICTIONARY. The loop is attached at its ends to two short pieces of platinum wire, which pa through the gla of the bulb and around which the gla is fused. As platinum has almost exactly the same coefficient of heat-expansion as gla , the wires do not cause the gla to crack. The proce of manufacture includes the preparation of the filament. This is made from paper, silk, bamboo fibre, tamidine, q. v., or other material. After shaping into the form of the filament the material is carbonized at a high heat, while embedded in charcoal, or otherwise protected from the air. The flashing proce (see Flashing of incandescent Lamp Carbons) may also be applied. The attachment to the platinum wires is effected by a minute clamp or by electric soldering. The loop is inserted and secured within the open globe, which the gla blower nearly closes, leaving one opening for exhaustion. The air is pumped out, perhaps first by a piston pump, but always at the end by a mercurial air pump. (See Pump, Gei ler--and others.) As the exhaustion becomes high a current is pa ed through the carbons heating them eventually to white heat so as to expel occluded gas. The occluded gases are exhausted by the pump and the lamp is sealed by melting the gla with a blowpipe or blast-lamp flame. For the exhaustion several lamps are usually fastened together by branching gla tubes, and are sealed off one by one. The incandescent lamps require about 3.5 watts to the candle power, or give about 12 sixteen-candle lamps to the horse power expended on them. Generally incandescent lamps are run in parallel or on multiple arc circuits. All that is nece ary in such distribution systems is to maintain a proper potential difference between the two leads acro which the lamps are connected. In the manufacture of lamps they are brought to an even resistance and the proper voltage at which they should be run is often marked upon them. This may be fifty volts and upward. One hundred and ten volts is a very usual figure. As current one ampere for a fifty-volt, or about one-half an ampere for a one hundred and ten volt lamp is employed.