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. This is accomplished by having
two terminals at one end of the tube, which are connected to choke
coils, which in turn are connected to a single coil (auto) transformer.
The alternating current supply mains are connected to wires tapping
different parts of the coil of the auto transformer. The center of
the coil of the auto transformer is connected through an induction
coil to the other end of the tube. By this means the alternating
current impulses are sent through the tube in one direction, one half
cycle from one of the pairs of terminals of the tube, the other half
cycle from the other terminal. Thus pulsating direct current, kept
constant by the induction coil, flows through the tube, the pulsations
overlapping each other by the magnetic action of the choke coils. This
alternating current lamp is started by the high voltage discharge
method. It has a 50-inch length of tube, consuming about 400 watts on
110 volts. Its efficiency is a little less than that of the direct
current lamp.
[Illustration: DIAGRAM OF COOPER-HEWITT LAMP FOR USE ON ALTERNATING
CURRENT.
The mercury arc is inherently for use on direct current, but by means
of reactance coils, it can be operated on alternating current.]
THE LUMINOUS OR MAGNETITE ARC LAMP
About 1901 Dr. Charles P. Steinmetz, Schenectady, N. Y., studied the
effect of metallic salts in the arc flame. Dr. Willis R. Whitney,
also of Schenectady, and director of the research laboratory of the
organization of which Dr. Steinmetz is the consulting engineer,
followed with some further work along this line. The results of this
work were incorporated in a commercial lamp called the magnetite arc
lamp, through the efforts of C. A. B. Halvorson, Jr., at Lynn, Mass.
The negative electrode consists of a pulverized mixture of magnetite
(a variety of iron ore) and other substances packed tightly in an iron
tube. The positive electrode is a piece of copper sheathed in iron to
prevent oxidization of the copper. The arc flame gives a brilliant
white light, and, similar to the mercury arc, is inherently limited to
direct current. It burns in the open air at about 75 volts. The lamp is
made for 4-ampere direct current series circuits and consumes about 310
watts and has an efficiency of about 11½ lumens per watt.
[Illustration: LUMINOUS OR MAGNETITE ARC LAMP, 1902.
This has a negative electrode containing magnetite which produces a
very luminous white flame in the arc stream.]
The negative (iron tube) electrode now has a life of about 350 hours.
Later, a higher efficiency, 4-ampere electrode was made which has
a shorter life but gives an efficiency of about 17 l-p-w, and a
6.6-ampere lamp was also made giving an efficiency of about 18 l-p-w
using the regular electrode. This electrode in being consumed gives
off fumes, so the lamp has a chimney through its body to carry them
off. Some of the fumes condense, leaving a fine powder, iron oxide, in
the form of rust. The consumption of the positive (copper) electrode
is very slow, which is opposite to that of carbon arc lamps on direct
current. The arc flame is brightest near the negative (iron tube)
electrode and decreases in brilliancy and volume as it nears the
positive (copper) electrode.
[Illustration: DIAGRAM OF SERIES MAGNETITE ARC LAMP.
The method of control, entirely different from that of other arc lamps,
was invented by Halvorson to meet the peculiarities of this arc.]
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. This allows
the lower electrode to fall a fixed distance, about seven-eighths of
an inch, drawing the arc, whose voltage is then about 72 volts. As the
negative electrode is consumed, the length and voltage of the arc
increases when a magnet, in shunt with the arc, becomes sufficiently
energized to close the contacts in the circuit of the starting magnet
causing the electrode to pick up and start off again.
MERCURY ARC RECTIFIER FOR MAGNETITE ARC LAMPS
[Illustration: MERCURY ARC RECTIFIER TUBE FOR SERIES MAGNETITE ARC
LAMPS, 1902.
The mercury arc converted the alternating constant current into direct
current required by the magnetite lamp.]
As the magnetite arc requires direct current for its operation, the
obvious way to supply a direct constant current for series circuits
is to rectify, by means of the mercury arc, the alternating current
obtained from a constant current transformer. The terminals of the
movable secondary coil of the constant current transformer are
connected to the two arms of the rectifier tube. One end of the series
circuit is connected to the center of the secondary coil. The other
end of the series circuit is connected to a reactance which in turn
is connected to the pool of mercury in the bottom of the rectifier
tube. One-half of the cycle of the alternating current goes from the
secondary coil to one arm of the rectifier tube through the mercury
vapor, the mercury arc having already been started by a separate
starting electrode. It then goes to the pool of mercury, through
the reactance and through the series circuit. The other half cycle
of alternating current goes to the other arm of the rectifier tube,
through the mercury vapor, etc., and through the series circuit. Thus a
pulsating direct current flows through the series circuit, the magnetic
action of the reactance coil making the pulsations of current overlap
each other, which prevents the mercury arc from going out.
[Illustration: EARLY MERCURY ARC RECTIFIER INSTALLATION.]
INCANDESCENT LAMP DEVELOPMENTS, 1894–1904
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.
These lamps were made in sizes from 20 to 100 candlepower. The arc lamp
was more desirable for larger units.
The dry battery was made in small units of 2, 3 and 5 cells, so that
lamps of about ⅛ to 1 candlepower were made for 2½, 3½ and 6½ volts,
for portable flashlights. It was not however until the tungsten
filament was developed in 1907 that these flashlights became as popular
as they now are. For ornamental lighting, lamps were supplied in round
and tubular bulbs, usually frosted to soften the light.
[Illustration: THE MOORE TUBE LIGHT, 1904.
This consisted of a tube about 1¾ inches in diameter and having a
length up to 200 feet, in which air at about one thousandth part
of atmospheric pressure was made to glow by a very high voltage
alternating current.]
THE MOORE TUBE LIGHT
Geissler, a German, discovered sixty odd years ago, that a high voltage
alternating current would cause a vacuum tube to glow. This light
was similar to that obtained by Hawksbee over two hundred years ago.
Geissler obtained his high voltage alternating current by a spark
coil, which consisted of two coils of wire mounted on an iron core.
Current from a primary battery passed through the primary coil, and
this current was rapidly interrupted by a vibrator on the principle of
an electric bell. This induced an alternating current of high voltage
in the secondary coil as this coil had a great many more turns than
the primary coil had. Scientists found that about 70 per cent of the
electrical energy put into the Geissler tube was converted into the
actual energy in the light given out.
In 1891 Mr. D. McFarlan Moore, an American, impressed with the fact
that only one-half of one per cent of the electrical energy put into
the carbon-incandescent lamp came out in the form of light, decided to
investigate the possibilities of the vacuum tube. After several years
of experiments and the making of many trial lamps, he finally, in 1904,
made a lamp that was commercially used in considerable numbers.
[Illustration: DIAGRAM OF FEEDER VALVE OF MOORE TUBE.
As the carbon terminals inside the tube absorbed the very slight
amount of gas in the tube, a feeder valve allowed gas to flow in the
tube, regulating the pressure to within one ten thousandth part of
an atmosphere above and below the normal extremely slight pressure
required.]
The first installation of this form of lamp was in a hardware store
in Newark, N. J. It consisted of a glass tube 1¾ inches in diameter
and 180 feet long. Air, at a pressure of about one-thousand part of
an atmosphere, was in the tube, from which was obtained a pale pink
color. High voltage (about 16,000 volts) alternating current was
supplied by a transformer to two carbon electrodes inside the ends of
the tube. The air had to be maintained within one ten-thousandth part
of atmospheric pressure above and below the normal of one-thousandth,
and as the rarefied air in the tube combined chemically with the carbon
electrodes, means had to be devised to maintain the air in the tube at
this slight pressure as well as within the narrow limits required.
This was accomplished by a piece of carbon through which the air could
seep, but if covered with mercury would make a tight seal. 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. Thus air could seep through this carbon rod
until the proper amount was fed into the main tube. When the current
came back to normal the electro-magnet lowered the floating glass tube
which raised the height of the mercury and covered the carbon rod, thus
shutting off the further supply of air.
As there was a constant loss of about 400 watts in the transformer,
and an additional loss of about 250 watts in the two electrodes, the
total consumption of the 180-foot tube was about 2250 watts. Nitrogen
gas gave a yellow light, which was more efficient and so was later
used. On account of the fixed losses in the transformer and electrodes
the longer tubes were more efficient, though they were made in various
sizes of from 40 to 200 feet. The 200-foot tube, with nitrogen, had an
efficiency of about 10 lumens per watt. Nitrogen gas was supplied to the
tube by removing the oxygen from the air used. This was accomplished by
passing the air over phosphorous which absorbed the oxygen.
Carbon dioxide gas (CO_{2}) gave a pure white light but at about
half the efficiency of nitrogen. The gas was obtained by allowing
hydrochloric acid to come in contact with lumps of marble (calcium
carbonate) which set free carbon dioxide and water vapor. The latter
was absorbed by passing the gas through lumps of calcium chloride. The
carbon dioxide tube on account of its daylight color value, made an
excellent light under which accurate color matching could be done. A
short tube is made for this purpose and this is the only use which the
Moore tube now has, owing to the more efficient and simpler tungsten
filament incandescent lamp.
THE OSMIUM LAMP
Dr. Auer von Welsbach, the German scientist who had produced the
Welsbach gas mantle, invented an incandescent electric lamp having a
filament of the metal osmium. It was commercially introduced in Europe
in 1905 and a few were sold, but it was never marketed in this country.
It was generally made for 55 volts, two lamps to burn in series on
110-volt circuits, gave about 25 candlepower and had an initial
efficiency of about 5½ lumens per watt. It had a very fair maintenance
of candlepower during its life, having an average efficiency of about
5 l-p-w. Osmium is a very rare and expensive metal, usually found
associated with platinum, and is therefore very difficult to obtain.
Burnt out lamps were therefore bought back in order to obtain a supply
of osmium. It is also a very brittle metal, so that the lamps were
extremely fragile.
[Illustration: OSMIUM LAMP, 1905.
This incandescent lamp was used in Europe for a few years, but was
impractical to manufacture in large quantities as osmium is rarer and
more expensive than platinum.]
THE GEM LAMP
Dr. Willis R. Whitney, of Schenectady, N. Y., had invented an
electrical resistance furnace. This consisted of a hollow carbon tube,
packed in sand, through which a very heavy current could be passed.
This heated the tube to a very high temperature, the sand preventing
the tube from oxidizing, so that whatever was put inside the tube
could be heated to a very high heat. Among his various 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.
[Illustration: GEM LAMP, 1905.
This incandescent lamp had a graphitized carbon filament obtained by
the heat of an electric furnace, so that it could be operated at 25 per
cent higher efficiency than the regular carbon lamp. This lamp is in
the exhibit of Edison lamps in the Smithsonian Institution.]
This lamp was put on the market in 1905 and was called the Gem or
metallized carbon filament lamp as such a carbon filament had a
resistance characteristic similar to metals. At first it had two single
hair pin filaments in series which in 1909 were changed to a single
loop filament like the carbon lamp.
In 1905 the rating of incandescent lamps was changed from a candlepower
to a wattage basis. The ordinary 16-candlepower carbon lamp consumed
50 watts and was so rated. The 50-watt Gem lamp gave 20 candlepower,
both candlepower ratings being their mean candlepower in a horizontal
direction. The Gem lamp was made for 110-volt circuits in sizes from
40 to 250 watts. The 50-watt size was the most popular, many millions
of which were made before the lamp disappeared from use in 1918. The
lamp was not quite as strong as the carbon lamp. Some Gem lamps for
series circuits were also made, but these were soon superseded by the
tungsten-filament lamp which appeared in 1907.
THE TANTALUM LAMP
[Illustration: TANTALUM LAMP, 1906.
The tantalum filament could be operated at 50 per cent greater
efficiency than that of the regular carbon incandescent lamp. This lamp
is in the exhibit of Edison lamps in the Smithsonian Institution.]
Dr. Werner von Bolton, a German physicist, made an investigation of
various materials to see if any of them were more suitable than carbon
for an incandescent-lamp filament. After experimenting with various
metals, tantalum was tried. Tantalum had been known to science for
about a hundred years. Von Bolton finally obtained some of the pure
metal and found it to be ductile so that it could be drawn out into a
wire. As it had a low specific resistance, the wire filament had to
be much longer and thinner than the carbon filament. A great number
of experimental lamps were made so that it was not until 1906 that
the lamp was put on the market in this country. It had an initial
efficiency of 5 lumens per watt and a good maintenance of candle power
throughout its life, having an average efficiency of about 4¼ l-p-w.
The usual sizes of lamps were 40 and 80 watts giving about 20 and 40
candlepower respectively. It was not quite as strong as the carbon
lamp, and on alternating current the wire crystallized more rapidly,
so that it broke more easily, giving a shorter life than on direct
current. It disappeared from use in 1913.
INVENTION OF THE TUNGSTEN LAMP
Alexander Just and Franz Hanaman in 1902 were laboratory assistants
to the Professor of Chemistry in the Technical High School in Vienna.
Just was spending his spare time in another laboratory in Vienna,
attempting to develop a boron incandescent lamp. In August of that year
he engaged Hanaman to aid him in his work. They conceived the idea of
making a lamp with a filament of tungsten and for two years worked on
both lamps. The boron lamp turned out to be a failure. Their means
were limited; Hanaman’s total income was $44 per month and Just’s was
slightly more than this. In 1903 they took out a German patent on a
tungsten filament, but the process they described was a failure because
it produced a filament containing both carbon and tungsten. The carbon
readily evaporated and quickly blackened the bulb when they attempted
to operate the filament at an efficiency higher than that possible with
the ordinary carbon filament. Finally in the latter part of the next
year (1904) they were able to get rid of the carbon and produced a pure
tungsten filament.
Tungsten had been known to chemists for many years by its compounds,
its oxides and its alloys with steel, but the properties of the pure
metal were practically unknown. It is an extremely hard and brittle
metal and it was impossible at that time to draw it into a wire. Just
and Hanaman’s process of making a pure tungsten filament consisted of
taking tungsten oxide in the form of an extremely fine powder, reducing
this to pure tungsten powder by heating it while hydrogen gas passed
over it. The gas combined with the oxygen of the oxide, forming water
vapor which was carried off, leaving the tungsten behind.
The tungsten powder was mixed with an organic binding material, and
the paste was forced by very high pressure through a hole drilled in
a diamond. This diamond die was necessary because tungsten, being so
hard a substance, would quickly wear away any other kind of die. The
thread formed was cut into proper lengths, bent the shape of a hair
pin and the ends fastened to clamps. Current was passed through the
hair pin in the presence of hydrogen gas and water vapor. The current
heated the hair pin, carbonized the organic binding material in it, the
carbon then combining with the moist hydrogen gas, leaving the tungsten
particles behind. These particles were sintered together by the heat,
forming the tungsten filament. Patents were applied for in various
countries, the one in the United States on July 6, 1905.
The two laboratory assistants in 1905 finally succeeded in getting
their invention taken up by a Hungarian lamp manufacturer. By the end
of the year lamps were made that were a striking success for they could
be operated at an efficiency of 8 lumens per watt. They were put on
the American market in 1907, the first lamp put out being the 100-watt
size for 110-volt circuits. This was done by mounting several hair pin
loops in series to get the requisite resistance, tungsten having a
low specific resistance. The issue of the American patent was delayed
owing to an interference between four different parties, each claiming
to be the inventor. After prolonged hearings, one application having
been found to be fraudulent, the patent was finally granted to Just and
Hanaman on February 27, 1912.
[Illustration: TUNGSTEN LAMP, 1907.
The original 100 watt tungsten lamp was nearly three times as efficient
as the carbon lamp, but its “pressed” filament was very fragile. This
lamp is in the exhibit of Edison lamps in the Smithsonian Institution.]
This “pressed” tungsten filament was quite fragile, but on account of
its relatively high efficiency compared with other incandescent lamps,
it immediately became popular. Soon after its introduction it became
possible to make finer filaments so that lamps for 60, 40 and then 25
watts for 110-volt circuits were made available. Sizes up to 500 watts
were also made which soon began to displace the enclosed carbon arc
lamp. Lamps were also made for series circuits in sizes from 32 to 400
candlepower. These promptly displaced the carbon and Gem series lamps.
The high efficiency of the tungsten filament was a great stimulus to
flashlights which are now sold by the millions each year. The lighting
of railroad cars, Pullmans and coaches, with tungsten lamps obtaining
their current from storage batteries, soon superseded the gas light
formerly used. In some cases, a dynamo, run by a belt from the car
axle, kept these batteries charged.
[Illustration: DRAWN TUNGSTEN WIRE LAMP, 1911.
Scientists had declared it impossible to change tungsten from a brittle
to ductile metal. This, however, was accomplished by Dr. Coolidge, and
drawn tungsten wire made the lamp very sturdy. This lamp is in the
exhibit of Edison lamps in the Smithsonian Institution.]
DRAWN TUNGSTEN WIRE
After several years of patient experiment, Dr. William D. Coolidge
in the research laboratory of a large electrical manufacturing
company at Schenectady, N. Y., invented a process for making tungsten
ductile, a patent for which was obtained in December, 1913. Tungsten
had heretofore been known as a very brittle metal, but by means of
this process it became possible to draw it into wire. This greatly
simplified the manufacture of lamps and enormously improved their
strength. Such lamps were commercially introduced in 1911.
With drawn tungsten wire it was easier to coil and therefore
concentrate the filament as required by focusing types of lamps. The
automobile headlight lamp was among the first of these, which in 1912
started the commercial use of electric light on cars in place of oil
and acetylene gas. On street railway cars the use of tungsten lamps,
made possible on this severe service by the greater sturdiness of
the drawn wire, greatly improved their lighting. 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.
[Illustration: 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 lamp is not used as an
illuminant in this country, but is valuable for use in the purification
of water.]
THE QUARTZ MERCURY VAPOR ARC LAMP
By putting a mercury arc in a tube made of quartz instead of glass,
it can be operated at a much higher temperature and thereby obtain a
greater efficiency. Such a lamp, however, is still largely deficient in
red rays, and it gives out a considerable amount of ultra-violet rays.
These ultra-violet rays will kill bacteria and the lamp is being used
to a certain extent for such purpose as in the purification of water.
These rays are very dangerous to the eyes, but they are absorbed by
glass, so as an illuminant, a glass globe must be used on the lamp.
These lamps appeared in Europe about 1912 but were never used to any
extent in this country as an illuminant. They have an efficiency of
about 26 lumens per watt. Quartz is very difficult to work, so the cost
of a quartz tube is very great. The ordinary bunsen gas flame is used
with glass, but quartz will only become soft in an oxy-hydrogen or
oxy-acetylene flame.
[Illustration: GAS FILLED TUNGSTEN LAMP, 1913.
By operating a coiled filament in an inert gas, Dr. Langmuir was able
to greatly increase its efficiency, the gain in light by the higher
temperature permissible, more than offsetting the loss of heat by
convection of the gas. This lamp is in the exhibit of Edison lamps in
the Smithsonian Institution.]
THE GAS-FILLED TUNGSTEN LAMP