Electrical Illuminating Engineering

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1908 Excerpt: ...are placed horizontally above the glower which is itself also in a horizontal position. These heaters are in the circuit when the lamp is turned on, but as the glower heats up, the current through it actuates an electromagnet which is connected in series with the glower and which opens the heater circuit. The difficulties experienced from the leakage of electricity through the porcelain and the unequal expansion of the platinum and porcelain are overcome by using only a pure and soft grade of porcelain. The guaranteed life of the heater tube is 2500 hours. Numerous attempts have been made to do away with the matter of preliminary heating, but the fact remains and is the chief drawback to the universal adoption of the lamp. In some cases as on ship-board where there might be uncertainty in the action of an automatic device, the heaters are connected by means of a third wire and switch in such a manner that after the lamp is lighted the switch can be opened and the heaters cut out, thus eliminating the necessity of an automatic cut-out. The peculiar characteristic of the glower, which is shared to some extent by nearly all electrolytes, namely, a decided negative temperature coefficient of resistivity, necessitates the introduction of a compensating resistance which should have a large positive temperature coefficient of resistivity and thus prevent an excess of current from passing through the glower, fusing and destroying it. Pure iron wire was found best adapted for the material of this resistance and it is mounted in a glass tube filled with an inert gas, preferably hydrogen, to prevent rust and deterioration. Since the temperature of this wire when in service, depends on the rate at which heat is conducted away from it, the final adjustment of the ballas...