From the 1926 book Edison, the Man and His Work.
EDITOR’S NOTE: There is one term which, if explained, makes this article readable by all. “Carbonizing” is the process of changing of a material (which contains carbon) into a more pure form of carbon. Charcoal is carbonized wood.
In the spring of 1879, metallic-wire lamps were privately exhibited at Menlo to members of the syndicate. Several lamps with platinum burners were “hooked up” in series in the machine-shop; current being furnished, according to Francis Jehl, by a dynamo “of the Gramme type.” The exhibition was not enheartening. Current was turned on. “A little more juice,” said Edison to Kruesi; and a second time, “A little more.” For a fleeting moment one lamp gave forth “a light like a star in the distance.” Then followed an explosion—a puff— darkness! Batchelor removed the wrecked lamp; inserted a fresh one. The same thing happened. One or two more trials were made, with like finale. “After that exhibition,” commented Jehl, “we had a house-cleaning at the laboratory.”
Nevertheless, Edison was making progress. First, he had learned that the incandescing substance must be hermetically enclosed in a container (now known as a “bulb”) formed entirely of glass and exhausted of air as thoroughly as possible. Thus enclosed, his platinum wire would yield, without melting, a light of twenty-five candles, whereas in the open air it would melt while yielding but four candles. Second, he had learned that when the air was being pumped out, a current must be sent through the incandescing substance.
He noticed that, even with high vacuum, oxygen appeared to be present to a perplexing extent, hastening the destruction of his platinum wire. This oxygen, he reasoned, must be held in the material of the wire when the wire was sealed into the glass; perhaps, if the wire were kept aglow while pumping was under way, the oxygen might be driven from the wire, whereupon it would be pumped out as the free air was. Tests showed his reasoning was correct.
He now returned to carbon filaments, and returned to stay, taking with him his invaluable new knowledge. In the case of carbon, it was realized that the importance of passing a current through the burner while a vacuum was being produced, was even greater than in the case of the metal wires; for carbon in its more porous states has a marked property of absorbing (or occluding) gases—a common example being afforded by charcoal, which by virtue of this property is of help in preserving foods.
Through his experiments with platinum, Edison had learned something else: though platinum had a melting-point relatively too low for his purpose, and though it was inferior in light-giving quality, yet it was long to play an essential part in the construction of incandescent lamps. For it was found to have the same amount of expansion with heat (“coefficient of expansion”), as glass had; hence it was used as the material of the “leads,” the wires that respectively brought current to the lamp and conveyed it from the lamp. Consequently no gaps developed to cause leakage at the points where the wires were sealed into the glass. Leads were made of platinum for many years, but platinum was costly and search was therefore begun for a substitute, which luckily was discovered through the use in combination of two metals whose joint coefficient of expansion was of proper value.
|1880 patent drawing showing wires going into the light bulb.|
From the date of the invention of the phonograph, Edison had been regarded by the gentlemen of the press as a likely source of “copy.” It was not long before the objective of his new labors became known. He believed, so it transpired, that the electric current could be subdivided; more than that, he was proposing to subdivide it. If outside of the Menlo Park organization and a few of Edison’s friends, like Professor Barker, there were experts either at home or abroad who agreed with him in belief or who anticipated a successful outcome for his experiments, they neglected to say so. On the contrary, William H. (later Sir William) Preece, a distinguished English electrician, somewhat contemptuously declared, “… the subdivision of the light is an absolute ignis fatuus”; thus supplying a catch-phrase that was to return boomerang-like upon its inventor. A committee of the House of Commons met, with Dr. Lyon Playfair (later Baron Playfair of St. Andrews) as chairman, to take counsel upon the matter of electric lighting; but its report dismissed Edison with short shrift indeed.
More graciously, more judicially, but hardly more hopefully, the famed John Tyndall said in a lecture before the Royal Institution: “Edison has the penetration to seize the relationship of facts and principles and the art to reduce them to novel and concrete combinations. Hence, though he has thus far accomplished nothing new in relation to the electric light, an adverse opinion as to his ability to solve the complicated problem on which he is engaged would be unwarranted. . . . Knowing something of the intricacy of the practical problem, I should certainly prefer seeing it in Mr. Edison’s hands to having it in mine.”
|Early Edison light bulb, courtesy of Wikimedia contributor, Terren.|
Others were much less courteous and reserved. ‘Dreamer,’ ‘fool,’ ‘boaster’ were among the appellations bestowed upon him by unbelieving critics. Ridicule was heaped upon him in the public prints, and mathematics were [sic] called into service by learned men to settle the point forever that he was attempting the utterly impossible.
Meanwhile, Edison was cultivating his garden. Of all substances, carbon has the maximum fusing-point (7000 degrees F., equivalent to about 3900 degrees C.); but this advantage alone was not enough. Carbon must, for Edison’s purpose, be formed into a homogeneous, stable burner of properly tenuous cross-section. More than a quarter-century later, Edison, speaking in a general way of the obstructions encountered, had this to say: “Just consider this; we have an almost infinitesimal filament heated to a degree which it is difficult for us to comprehend, and it is in a vacuum, under conditions of which we are wholly ignorant.
“You cannot use your eyes to help you in the investigation, and you really know nothing of what is going on in that tiny bulb. I speak without exaggeration when I say that I have constructed three thousand different theories in connection with the electric light, each one of them reasonable and apparently likely to be true. Yet in two cases only, did my experiments prove the truth of my theory. My chief difficulty was in constructing the carbon filament, the incandescence of which is the source of the light.”
|Drawing of the “Interior of the Laboratory at Menlo”|
Edison persistently studied not only carbon as luminous material but also high vacua and the means for obtaining them in an increasingly suitable degree. By about October 1st, 1879, he had a pump that was capable of creating a vacuum as high as one one-millionth part of an atmosphere. “If he [Edison] wanted material,” wrote Francis Upton, “he always made it a principle to have it at once, and never hesitated to use special messengers to get it. I remember in the early days of the electric light he wanted a mercury pump for exhausting the lamps.
He sent me to Princeton to get it. I got back to Metuchen late in the day, and had to carry the pump over to the laboratory on my back that evening, set it up, and work all night and the next day getting results.” Finally it occurred to Edison, still vainly pondering a carbon conductor that should be small enough and durable enough, to see what might be done with cotton sewing-thread. Of a compacted, fibrous structure and certainly with a small cross-section, this might, when carbonized, turn out to be the very thing.
For carbonizing, a short piece of the thread, bent into hairpin shape, was placed in a nickel mold, and then the mold was allowed to remain for five hours in a muffle-furnace. After the mold was removed from the furnace and became cool, it was opened; and then the carbon phantom of thread had to be withdrawn from the mold and sealed into a bulb. It was a task of fortitude and delicacy. All night, the next day, and another night, Edison and Batchelor kept at it. From a whole spool of thread, they finally succeeded in getting a carbonized piece that did not break while being taken from the mold.
“It was necessary,” Edison related, “to take it to the glass-blower’s house.” With the utmost precaution Batchelor took up the precious carbon, and I marched after him, as if guarding a mighty treasure. To our consternation, just as we reached the glass-blower’s bench, the wretched carbon broke. We turned back to the main laboratory and set to work again. It was late in the afternoon before we had produced another carbon, which was again broken by a jeweler’s screwdriver falling against it. But we turned back again, and before night, the carbon was completed and inserted in the lamp. The bulb was exhausted of air and sealed, the current turned on, and the sight we had so long desired to see met our eyes.” The date was October 21st.
That lamp continued at incandescence for more than forty hours, while Batchelor, Edison, and others watched it and bets were laid as to how long it was going to burn.
Then the light failed. But the sewing-thread lamp had rendered its reasonable service and won a place in the story of modern invention. It had shown that carbon would sustain temperatures before which platinum would quickly melt; that subdivision of the electric current was truly possible. Some thirteen months had passed in experiments and more than $40,000 had been spent; but Edison and Batchelor now felt that the expenditure of time and money had been justified.
As for Batchelor, it may be doubted whether anybody else at Menlo—even Edison himself—could have accomplished what he accomplished with that brittle filament.
Nevertheless, those forty hours, although they established a principle, did not answer to the commercial requirements for a stable burner. Forthwith Edison inaugurated the most whole-hearted carbonizing-bee on record. Among the things he carbonized were:
cardboards of many kinds
cotton soaked in boiling tar drawing-paper in great variety
paper saturated with tar
red hairs from the beard of J. U. Mackenzie (who was staying at Menlo)
threads, cotton and linen, of all sorts
threads of fine size, plaited
threads treated with tarred lampblack
Of all the substances tested during this period, paper, however, appeared the most likely—so likely, indeed, from the more strictly commercial viewpoint, that Edison started the regular manufacture of lamps with looped filaments of carbonized paper. Scores of these were put into service, not merely within the laboratory but also in dwellings at Menlo and along the neighborhood roads. Doubters might cavil and wiseacres argue: folk travelled to the spot and went away to report that a new light was actually burning there.
|Caption under the picture reads, “New Jersey. — The Wizart of Electricity — Thomas. A. Edison experimenting the carbonized paper for his system of electric light, at his laboratory, Menlo Park. — From sketches by our special artist.”|