THE NEWEST ELECTRIC LIGHTS
One evening our boy friend entered the scientist's laboratory and found it more brilliantly illuminated than it ever had been before.
"Oh, I know," he said looking up at the ceiling, "those new electric lights up there are tungsten lamps. It certainly makes a difference in the looks of this place."
"Lights up all the dingy corners, doesn't it?" answered his friend. "You remember," he continued, "we talked last week about some of the new kinds of electric light and that made me think that I might just as well take advantage of what other scientists have done and install this newest kind of electric lamps."
From the ceiling were suspended several stationary fixtures with bright glass reflectors. The lamps the boy saw were somewhat larger than the usual electric light bulbs, and gave off a beautiful white light instead of the slightly yellowish illumination that comes from the ordinary ones. He saw that the filament from which the illumination came was not arranged in a series of horseshoe curves, as in the case of the ordinary globes, but that it was strung between the ends of cross trees, or "spiders," so that there was a greater total length of filament in the same size bulb than in the ones used before the invention of the tungsten lamp. It is a sight familiar enough to most boys in these days of the rapid adoption of new inventions, but it brought to the boy's mind a question that had often occurred to him before.
"Who invented tungsten lights?" he asked.
"Well, it would hardly be right to say that any one individual invented them, for they were really a development of science worked out by many men, who studied the problem for many years. This caused a number of very bitter lawsuits over the patents and brought about the imprisonment of one United States patent office official who was convicted of falsifying the records at Washington to help one of the inventors. This inventor was John Allen Heany, and his patents were rejected finally, the rights of the tungsten filament going to the General Electric Company. The name 'tungsten' is taken from the material of which filament, or the little wire which lights up in the globe, is made."
"What is tungsten?" asked the boy.
"Tungsten is a metal that for a great many years some of our most prominent chemists and scientific investigators declared could not be put to the use we see it here," answered the man.
Noticing that the boy leaned forward in his chair, keen on his every word, the boy's friend continued his description of this strange metal that has been put to work lighting us in our march along the road of life.
He explained that tungsten, or wolfram, was discovered in 1781 and was named from the Swedish words "tung" (heavy) and "sten" (stone). The mineral is not found in a pure state but rather in wolframite, which is what the scientists call a tungstate of iron and manganese, and also in schoolite which is calcium tungstate. Pure tungsten is bright steel gray, very hard, and very heavy. It is one of the most brittle of all the metals and for that reason was put to very few uses before the invention of the tungsten lamp. It was most commonly used, however, in various steel processes, to harden the metal.
From the time Edison invented the incandescent lamp in 1879, right up to the present electricians have tried to get a better electric light filament. A number of persons conceived the idea of making a filament of tungsten on account of its peculiar characteristics, which seemed to be just about the ones needed for the ideal electric light globe.
In its fundamental idea the tungsten lamp is not very greatly different from the early Edison incandescent lamps, but in the application of the principle there is half a century of accomplishment packed into a little over a quarter of a century of years. Edison saw that he must have a filament that would carry the current of electricity, but yet one which would be of such high resistance that it would not take up all the current fed to it. He saw that he had to have a filament that would heat to incandescence with the electrical current, and yet one that would stand a certain amount of wear and tear, and which would not be consumed by the heat. To obtain the latter effect he put his filament in an air-tight glass globe from which the atmosphere was exhausted, leaving it in a vacuum. As there was no air, there was no oxygen, and hence there could be no oxidization, or, in other words, combustion of the filament.
Edison thought that success lay in a carbon filament, and in these early days when he was experimenting at his Menlo Park laboratory he carbonized just about everything he could lay his hands on and tried heating the result to incandescence in the vacuum globe. Finally, on October 21, he carbonized a piece of cotton thread and put it in his vacuum globe in the form of a horseshoe loop. On connecting it with his electric circuit he was rewarded by seeing a brilliant incandescent light that lasted without dimming for forty straight hours.
What a dim, dingy little light it was in comparison to the world famous lights that Edison now puts forth! And yet in one way it was the most brilliant light that ever had shone in the world, for it showed mankind the pathway toward a complete system of electric lighting by incandescent lamps.
The carbonized cotton thread filament had many drawbacks, and Edison continued carbonizing various fabrics and fibres, including, it is said, some of the red hairs out of the beard of one of his loyal staff! At last he hit upon a filament made of carbonized Japanese bamboo that was very successful for a number of years, but this was later superseded by a cellulose mixture mechanically pressed out by dies.
Meanwhile, several investigators began work with tungsten and a similar metal called tantalum because of their extremely high melting points, high resistance, and other technical characteristics favourable for an incandescent filament.
For years they had no success because the metal was so very brittle that they could do nothing with it, but finally a filament of pressed tungsten was brought out. In this type of lamp several filament loops would be fused or welded together to make one complete filament. The result was a very fine light, but the little wire was too fragile to stand hard usage, and owing to the fact that the various connected loops were not all of exactly the same thickness, one frequently burned out far ahead of the others and caused early lamp failure.
The next step, and the one which a great many scientists had declared impossible, was the manufacture of a tungsten wire through a regular process of drawing it out through dies to the desired length, and in the desired thickness. The investigators had declared that in spite of all they could do, tungsten was too brittle ever to be drawn into wire. In the latest methods this is accomplished with such perfection that tungsten wire of 0.0015 of an inch in diameter is produced.
"With the invention of a method for drawing out tungsten wire," continued the scientist, "an almost ideal lamp was practically accomplished. The wire simply was strung on the spiders or cross pieces, and a filament of almost any length giving almost any desired candlepower light could be used.
"You see in an incandescent light the higher the melting point of the filament the greater the quantity of light for the amount of electricity used. Also tungsten has a low vapour tension, which prevents discolouration of the globe by the evaporation of the filament. It also has other advantages which are too technical for us to go into.
"Of course, tungsten lamps still have the drawback of being rather delicate. When not in use, and when the filament is cold, it is apt to break with rough treatment, but when lighted the filament, being at a white heat, is more durable. This delicacy of the tungsten lamp is the reason the fixtures for most of them are placed in stationary positions, rather than on swinging drop cords, as is the case with so many carbon incandescent lights.
"While the tungsten lamp is far from perfect, it is a great advance over other forms, and an advance in the right direction, for it gives a better light with a smaller consumption of electricity than other types. I think your father will agree with me that anything that will help ever so little to reduce the high cost of living is a benefit."
"But," answered the boy, "there are other new kinds of electric lights besides tungsten, aren't there?"
"Oh, of course, but they are hardly as generally used as the tungsten light. There is the mercury light about which you read in 'The Second Boys' Book of Inventions,' several new kinds of arc lights, the Nernst light, the tantalum lamp (which we know is much like the tungsten lamp with the exception that in the latter each loop of the wire can be made longer), and the new carbon dioxide gas electric light, which is a very good imitation of daylight.
"From all our little scientific journeys you have doubtless formed the idea that light is not the simple thing it seems, and that the rays of different kinds of light will bear a limitless amount of study. Now some of the greatest scientists the world ever has known have spent the best part of their lives trying to produce a light that would duplicate the beautiful health-giving rays of the sun. This light we are speaking of comes as near to it as any."
He picked up a long glass test tube and holding it between his fingers said: "Now if this tube were exhausted of air to a vacuum, and we had an ingenious little device at each end which would allow just the right amount—no more, no less—of carbon dioxide gas to enter it, and also we had electrodes at either end, and connected them to an alternating current, we would have a rough model of the light that duplicates daylight.
"In actual practice the vacuum tubes are long, and turn upon themselves in many lengths. You have seen these lights in many places, for photographers, lithographers, dye works, textile mills, and all other places where the true light of day is necessary for the judgment of colours are adopting them for their night work."
"But the light is a ghastly pale blue," interrupted the boy. "It doesn't look like daylight to me."
"No, you are thinking of the mercury light, which also is strung around in tubes. That has a blue-greenish tinge to it, and gives people's faces a disagreeable greenish tinge, but this carbon dioxide electric light is white with a salmon pink tinge. Of course it isn't perfect, but the men who developed it from the work of others who started on this idea years ago, are constantly at work trying to improve it."