Henry Schroeder

“ The rate of electrical energy (electric power) is therefore proportional to the square of current multiplied by the resistance. The electrical unit of power is now called the Watt, named in honor of James Watt, the Englishman, who made great improvements to the steam engine about a century ago. Thus, watts = C2R and substituting the value of R from Ohm’s law, C = E/R, we get
Watts = Volts × Amperes
The watt is a small unit of electric power, as can be seen from the fact that 746 watts are equal to one horsepower. The kilowatt, kilo being the Greek word for thousand, is 1000 watts. ”

“ The use of argon gas, which has a poorer heat conductivity than nitrogen, made it possible to produce smaller lamps, 50-watt gas-filled lamps for 110-volt circuits now being the smallest available. In the present state of the art, a vacuum lamp is more efficient than a gas-filled lamp having a filament smaller than one consuming about half an ampere. Thus gas-filled lamps are not now practicable much below 100 watts for 220 volts, 50 watts for 110 volts, 25 watts for 60 volts, 15 watts for 30 volts, etc. ”

“ The first problem was therefore to design a dynamo that would give a constant pressure instead of constant current. He therefore reasoned that the internal resistance of the armature must be very low or the voltage would fall as current was taken from the dynamo. Scientists had shown that the most economical use of electricity from a primary battery was where the external resistance of the load was the same as the internal resistance of the battery, or in other words, 50 per cent was the maximum possible efficiency. ”

“ Convinced of the seeming impossibility of carbon, he turned his attention to platinum as a light giving element. Realizing the importance of operating platinum close to its melting temperature, he designed a lamp which had a thermostatic arrangement so that the burner would be automatically short circuited the moment its temperature became dangerously close to melting. The burner consisted of a double helix of platinum wire within which was a rod.44 When the temperature of the platinum became too high, the rod in expanding would short circuit the platinum. ”

“ The average candlepower of standard lighting lamps has increased from 16, which prevailed during the period prior to 1905, to over 60. The average wattage has not varied much during the past twenty-odd years, the average lamp now consuming about 55 watts. This indicates that the public is utilizing the improvement in lamp efficiency by increased illumination. The present most popular lamp is the 40-watt size which represents 20 per cent of the total demand. Second in demand is the 25-watt at 18 per cent and third, the 50-watt at 15 per cent of the total in numbers. ”

“ The object of all collections in the Divisions is to visualize broadly the steps by which advances have been made in each field of engineering; to show the layman the fundamental and general principles which are the basis for the developments; and to familiarize the engineer with branches of engineering other than his own. Normally when a subject is completely covered by a collection of objects, a paper is prepared and published describing the collection and the story it portrays. ”

“ Its light is very diffused and is practically devoid of red rays, so that red objects appear black in its light. The lamp consumes 31⁄2 amperes at 110 volts direct current (385 watts) having an efficiency of about 121⁄2 lumens per watt.
The mercury arc is peculiar in that it acts as an electric valve tending to let current flow through it only in one direction. Thus on alternating current, the current impulses will readily go through it in one direction, but the arc will go out in the other half cycle unless means are taken to prevent this. ”

“ In 1860 Way discovered that if an electric circuit was opened between mercury contacts a brilliant greenish colored arc was produced. Mercury was an expensive metal and as the carbon arc seemed to give the most desirable results, nothing further was done for many years until Dr. Peter Cooper Hewitt, an American, began experimenting73 with it. He finally produced an arc in vacuum in a one-inch glass tube about 50 inches long for 110 volts direct current circuits, which was commercialized in 1901. ”

“ Georg Simon Ohm was born in Bavaria, the oldest son of a poor blacksmith. With the aid of friends he went to college and became a teacher. It had been shown that the rate of transfer of heat from one end to the other of a metal bar is proportional to the difference of temperature between the ends. About 1825, Ohm, by analogy and experiment, found that the current in a conductor is proportional to the difference of electric pressure (voltage) between its ends. ”

“ The cost has gradually come down and the general average rate for which current is sold for lighting purposes is now about 41⁄2 cents. During the period 1880 to 1905 the average efficiency of carbon lamps throughout their life increased from about one to over 23⁄4 lumens per watt and their list price decreased from one dollar to twenty cents. The average amount of light obtained for one cent at first was about five candlepower hours and in 1904 it was increased to over thirty-six at the average rate then in effect. ”

“ While the aggregate demand of all the gas-filled tungsten lamps is a little over 20 per cent in numbers, they represent, on account of their greater efficiency and wattage, over half the amount of total candlepower used. In the United States about 85 per cent of all lamps are for the 110-volt range. About 5 per cent for 220 volts, 2 per cent for street series lighting, 3 per cent for street railway and 5 per cent for trainlighting and miscellaneous classes of service. ”

“ Edward Weston of Newark, New Jersey, also developed an arc lighting system. His commercial lamp had carbon rods, one above the other, and the arc was also differentially controlled. An oil dash pot prevented undue pumping of the carbons. His dynamo had a drum-wound armature, and had several horizontal field coils on each side of one pair of poles between which the armature revolved. The system was designed for about 20 amperes, each are taking about 35 volts. ”

“ Nollet’s original design was of a dynamo having several rows of permanent magnets mounted radially on a stationary frame, with an equal number of bobbins mounted on a shaft which rotated and had a commutator so direct current could be obtained. A company was formed to sell hydrogen gas for illuminating purposes, the gas to be made by the decomposition of water with current from this machine. Nollet died and the company failed, but it was reorganized as the Alliance Company a few years later to exploit the arc lamp. ”

“ When the lamp burned out the entire 1200 volts was impressed across this piece of paper, puncturing it and so short circuiting the base terminals. Should one or more lamps go out on a circuit, the increase in current above the normal 3 amperes was prevented by an adjustable resistance, or an extra lot of lamps which could be turned on one at a time, connected to each circuit and located in the power station under the control of the operator. This system disappeared from use with the advent of the constant current transformer. ”

“ All his lamps had a thick carbon burner operating in nitrogen gas. They had a long glass tube closed at one end and the other cemented to a brass base through which the gas was put in. Heavy fluted wires connected the burner with the base to radiate the heat, in order to keep the joint in the base cool. The burner was renewable by opening the cemented joint. Farmer’s lamp consisted of a pair of heavy copper rods mounted on a rubber cork, between which a graphite rod was mounted. This was inserted in a glass bulb and operated in nitrogen gas. ”

“ The reason for the big difference in efficiency between the series and multiple direct-current arc is that in the latter a large amount of electrical energy (watts) is lost in the ballast resistance. While there is a considerable difference between the inherent efficiencies of the D. C. and A. C. arcs themselves, this difference is reduced in the67 multiple D. C. and A. C. arc lamps as more watts are lost in the resistance ballast of the multiple D. C. lamp than are lost in the reactance ballast of the multiple A. C. lamp.
This reactance gives the A. C. lamp what is called a “power-factor.” ”

“ Furthermore, as the voltage on street railway systems is subject to great changes, the candlepower of the tungsten filament has the advantage of varying but about half as much as that of the carbon lamp on fluctuating voltage.
Quartz Mercury Vapor Lamp, 1912.
The mercury arc if enclosed in quartz glass can be operated at much higher temperature and therefore greater efficiency. The light is still deficient in red but gives a considerable amount of ultra-violet rays which kill bacteria and are very dangerous to the eye. They can, however, be absorbed by a glass globe. ”

“ The peculiarities of the arc are such that Halvorson invented an entirely new principle of control. The electrodes are normally apart. In starting, they are drawn together by a starting magnet with sufficient force to dislodge the slag which forms on the negative electrode and which becomes an insulator when cold. Current then flows through the electrodes and through a series magnet which pulls up a solenoid breaking the circuit through the starting magnet. ”

“ Among his various83 experiments, he heated some carbon filaments and found that the high temperature changed their resistance “characteristic” from negative to positive. The ordinary carbon filament has a resistance when hot that is less than when it is cold, which was reversed after heating it to the high temperature Dr. Whitney was able to obtain. These filaments were made into lamps for 110-volt service and it was found that they could be operated at an efficiency of 4 lumens per watt. The lamps also blackened less than the regular carbon lamp throughout their life. ”

“ As the air pressure became low, an increased current would flow through the tube, the normal being about a tenth of an ampere. This accordingly increased the current flowing through the primary coil of the transformer. In series with the primary coil was an electro-magnet which lifted, as the current increased, a bundle of iron wires mounted in a glass tube which floated in mercury. The glass tube, rising, lowered the height of the mercury, uncovering a carbon rod cemented in a tube connecting the main tube with the open air. ”

“ With the development of a waterproof base in 1900, by the use of a waterproof cement instead of plaster of Paris to fasten the base to the bulb, porcelain at first and later glass being used to insulate the terminals of the base from each other, lamps could be exposed to the weather and give good results. Electric sign lighting therefore received a great stimulus, and lamps as low as 2 candlepower for 110 volts were designed for this purpose. Carbon lamps with concentrated filaments were also made for stereoptican and other focussing purposes. ”

“ The carbon series incandescent lamp, however, was more efficient if made for lower currents, so 31⁄2-, 4- and 51⁄2-ampere constant current transformers were made for incandescent lamps designed for these amperes. Later, however, with the advent of the tungsten filament, the 6.6-ampere series tungsten lamp was made the standard, as it was slightly more efficient than the lower current lamps, and was made in sizes from 32 to 400 cp. When the more efficient gas-filled tungsten lamps were developed, the sizes were further increased ”

“ This lamp is in the exhibit of Edison lamps in the Smithsonian Institution.
THE GAS-FILLED TUNGSTEN LAMP
The higher the temperature at which an incandescent lamp filament can be operated, the more efficient it becomes. The limit in temperature is reached when the material begins to evaporate rapidly, which blackens the bulb. The filament becoming thinner more quickly, thus rupturing sooner, shortens the life. If, therefore, the evaporating temperature can by some means be slightly raised, the efficiency will be greatly improved. ”

“ Dr. Walther Nernst, of Germany, investigating the rare earths used in the Welsbach mantle, developed an electric lamp having a burner, or “glower” as it was called, consisting of a mixture of these oxides. ”

“ One is of passing interest only. It consisted of a strip of platinum, the active length of which could be adjusted to fit the battery strength used, and was covered by a glass globe to protect it from draughts of air. The other, a carbon lamp, was the first real contribution to the art. It consisted of a rod of carbon operating in the vacuum above a column of mercury (Torrecellium vacuum) as in a barometer. A heavy platinum wire18 was sealed in the upper closed end of a large glass tube, and connected to the carbon rod by an iron clamp. ”

“ For 220-volt service lamps are made in sizes of from 25 to 1000 watts. For sign lighting service, 5-watt lamps of low voltage are made for use on a transformer located near the sign to reduce the 110 volts alternating current to that required by the lamps. Lamps are made from 5 to 100 watts for 30-volt service, such as is found in train lighting and in gas engine driven dynamo sets used in rural homes beyond the reach of central station systems. ”

“ He used his diaphragm thermostat to protect the platinum from melting, and, as now seems obvious but was not to all so-called electricians at that time, the thermostat was arranged to open circuit instead of short circuit the burner when it became too hot. This lamp apparently solved the problem, and, in order to protect the platinum from the47 oxygen of the air, he coated it with oxide of zirconium. Unfortunately zirconia, while an insulator at ordinary temperatures, becomes, as is now known, a conductor of electricity when heated, so that the lamp short circuited itself when it was lighted. ”