The Moore vapor tube glow lamp is manu factured in various forms, and is much valued for matching colors, owing to its close ap proximation to daylight conditions. By the em ployment of different vapors it can be made to yield blue, white, yellow or rose light. It re quires renewal of carbon dioxide after 1,000 hours' use, but the tubes will last four or five thousand hours. It is run on 110-volt circuits at 23 amperet.
The Incandescent The great attending the use of the arc system of lighting was that the light was too intense for most purposes required. inside. It could not be readily subdivided. From the earliest days of electric lighting, various inventors endeav ored to subdivide the light. The idea of using continuous conductors, instead of the discon tinuous as in arc lighting, was tried in almost every conceivable form. These conductors were to be heated to a white heat and rendered in candescent by the passage through them of an electric current. The great difficulty arose from the fact that to give useful results, the working temperature of the material was so near its melting point, that any slight increase in the current would destroy the conductor. In 1878 a great improvement was effected in the platinum filament incandescent lamp, which was obtained in a condition safely to withstand a much greater current strength. The filament was placed in a vacuum, and slowly heated therein. The occluded gases were slowly liberated, and it was discovered that if a high vacuum were maintained and the wire raised to a point just below its melting point, the point of fusion was raised, and the physical character of the metal was considerably changed. This lamp, how ever, was never a commercial success.
Various inventors experimented with the platinum lamp, enclosed in vacuo, but the great est improvement was made by the substitution of carbon filaments for platinum. This was done by an American, J. W. Starr, who em ployed plates inside a glass vessel containing a Torricellian vacuum. Many patents were taken out in all countries for lamps of various types, but none were commercially successful; many, perhaps, for the want of a cheap method of generating the electrical energy, as well as through fault of the lamp itself.
The advent of the first successful incandes cent lamp dates from about 1879, when Edison gave us the carbon incandescent lamp, and from that time the growth of the incandescent electric lighting industry has been extremely rapid.
Every such incandescent lamp consists of a carbon filament attached to two platinum wires, a glass bulb in which a vacuum is formed, and finally a threaded base attached to the bulb, and designed to hold the lamp in its socket.
The following is in a general way the method by which the lamps are made. The bulbs are blown at the glass factory whence the manu facturers obtain them directly. The first ma nipulation consists of preparing them for the filament. The nature of the filament varies with different systems. There are three kinds employed. Some (Swan) employ cotton threads; others gelatine or vitrified cellulose (Khotinski Lave-Fox) ; and others use vegetable fibres (Edison-Siemens). Finally, some employ a natural fibre submitted to a chemical process (Langhans Cruto Seel). Form is given to the filament according to its nature, either by means of a die, or between cylinders, or by cutting it out while in a plastic mass. The fibre thus obtained is transformed into compact carbon by prolonged baking at a high temperature in a crucible or by heating with the electric current itself. To give the filament homogeneity and the desired resistance a layer of carbon should be deposited on its surface. This deposit is affected in many ways. A very simple method termed Mashing') consists in immersing the fila ment in petroleum and raising it to a red 'heat in that liquid. The filament being cut to the desired length, Edison clamps the carbon with platinum wires and covers the points of attach ment with a layer of electrolytic copper ; Lave, Fox and Swan deposit a greater quantity of carbon there, while other manufacturers employ a special cement or solder. The filaments may be fixed in the bulb in two ways: either the two wires are fused into a piece of glass called the budge, which is next fused into the neck of the bulb • or else the wires are fixed sep arately on the edges of a glass socket, which is then fused into the bulb. A small tube is also fused to the top of the bulb in order to provide for the production of a vacuum. The exhaustion of the lamps takes place by means of mercury pumps. The vacuum obtained, the lamp is tested. Then the luminous intensity and the resistance when cold are measured. The dimensions of the filaments vary with the luminous intensity of the lamp; they should be proportionately greater as the normal intensity of the lamp is higher. These dimensions depend also upon the specific resistance of the carbon ized substance. As to the form of the section of the filament, the circular one is preferable because it presents the minimum resistance for a given surface.