The EVOLUTION of the X-RAY TUBE F. KRAISSL, SR. 501 Fifth Avenue, New York C i t ~
At the close of a previous article* outlining the history of the American chemical glassware industry the writer expressed the hope that further articles detailing the development df various special lines of the apparatus industry might prove generally welcome. In view of the fact that this year marks the 40th anniversary of RBntgen's discovery of X-rays, an historical note on the development and manufacture of X-ray tubes seems especially appropriate at this time. The writer is encouraged by his recollections of his close association with the earliest commercial production of X-ray tubes in this country to offer such a note. In his earliest publications on his famous discovery Professor Rontgen stated that the excitation of a Hittorf, Lenard, Crookes, or similar vacuum tube by means of a large Ruhmkorff , coil produced radiations
capable of causing considerable fluorescence of a distant screen of paper impregnated with barium platinocyanide. To these radiations he gave the name Xrays, which, therefore, should be authentic, although many prefer to honor the modest discoverer by designating them as Rontgen rays. When the first reports of Rontgen's work reached
TRRAISSL,
Of the chemical apparatus J. CHEM.EDUC..10, 519-23 (Sept., 1933).
this country the writer was associated with the late Emil Greiner, who at that time operated a glass apparatus shop in New York City and who was one of the the best glassblowers of his day. Although neither sketches, samples, nor detailed descriptions of Rontgen's tubes were available, the writer suggested a design similar to that illustrated in Figure 1. Mr. Greiner, himself, blew the tube, using small, flat aluminum dis-s with platinum-wire leads for the electrodes.
When the tube was finished we proceeded to evacuate it by means of a simple pump of the Sprengel type (Figure 2). When we judged that a sufficient degree of evacuation had been attained, the.tube was sealed off and connected to a small RuhmkorR coil operated by dry batteries (the only one available in the shop). The visible phenomenon obsemed was a bluish luminescence similar to that produced by a Geissler tube. Since we had no fluorescent screen ready t o hand, we placed some small metallic-objects on top of a loaded photographic plate-holder and made a short exposure. Upon development the plate revealed faint outlines of the objects we had laid upon its cover, assuring us that we had succeeded in producing some X-rays a t least. However, the effect was not sufficiently strong to satisfy us, and we decided to investigate the effect of higher tube evacuation. This time, guided more by instinct than by information, we heated the tube in the hope of facilitating the removal of occluded air. Apparently this expedient had the desired effect, for in a second trial with our Ruhmkorff coil we obtained practically no luminescence a t all aside from an occasional greenish flicker. This suxgested to us that
a more powerful coil might be necessary to operate so highly evacuated a tube. A friend of Mr. Greiner, a Mr. Splitdorf, who made such coils, supplied the largest he had on hand and our hopes were realized. This time the former greenish flicker was replaced by a steady greenish glow and the writer made the second test exposure by placing his hand upon the cover of the plate-holder. The developed plate showed the outline of the hand, with the bone structure clearly discernible. Little, if any, trace of these first experiments, performed in December, 1895, remains, savein the writer's memory. Early in 1896, however, it was generally known in this country that we had constructed successful X-ray tubes and everyone interested in the newly discovered phenomenon came to see us. Suggestions with regard to shape of the tubes, electrodes, and methods of evacuation were offered by various experimenters, among them Tesla, Thomson, Brackett, Goodspeed and many others. The first real help in the speedy production of tubes was the invention of the fluoroscope which made pos-
sible convenient testing of a tube without detachment from the vacuum line. The efficiency of the tube was judged by the clarity with which the bones of the hand could be seen upon the fluoroscopic screen. The priter had many such tests to make (see Figure 3). The X-ray had immediately captured the fancy of the press and was even a favorite topic in the comic papers. Commercial amusement exploiters seized their opportunity. One of the first quantity users of Greiner's X-ray tubes was a firm which contrived a nickel-in-the-slot machine to introduce the wonders of the X-ray to the general public. The device consisted of a cabinet containing a battery, RuhmkorE coil, X-ray tube and fluoroscope, and, of course, a coinactuated switch. The peep-show addict got a momentary view of the bones in his hand for his nickel investment, and the machines did a thriving business. Incidentally, as the tubes had to be of definite dimensions in order to fit into the cabinet, and as they were made up in lots of several dozen a t a time, their production was the first step toward the systematic manufacture of X-ray tubes. It was natural that the manufacturers of incandescent lamps, then engaged in a comparatively new industry, should also take up the production of X-ray tubes. The work was right in their line and their equipment was well adapted to it. In Thomson's book on X-rays, published in 1896, the advertisements of several such firms appeared, along with that of Emil Greiner (Figure 4). . he Greiner cut in Figure 4 shows one of the demonstration outfits advertised in his first X-ray circular early in 1896. Apparently there are now no copies of that early advertisement extant, but reference is made to it in a larger pamphlet issued in 1897 (see facsimile pages, Figures 5 and 6). Of course i t soon became necessary, in order to supply the demand for X-ray tubes, to adopt evacuating pumps similar to those used by the incandescent lamp manufacturers and to place the work on a quantity production basis. These pumps were of the so-called Geissler type and were later improved by the addition of a mechanical device for raising the mercury (Figure 7). They were fitted with manifolds attached to the pumps by means of ground-glass joints, so that several tubes could be evacuated simultaneously. The firm of Emil Greiner was essentially a custom shop in which special physical and chemical appa-
ratus was constructed to order and, as other manufacturers entered the X-rav field later in 1896 and earlv in 1897, no particular effort was made to expand the X-ray tube production, although we continued to produce tubes for our regular customers. Since there have been conflicting claims for the distinction of the first commercial X-ray tube production in this country, the writer has searched the trade literature with particular pains. The first advertisement of commercial X-ray tubes which he has been able t o discover appeared in the Electrical Review for June, 1886, when the firm of Emil Greiner was already in full production. It is the writer's opinion, based on the evidence available, that Emil Greiner was in fact the pioneer in this field in America. The writer doubts the existence of documentary evidence that any rival claimant made and sold an X-ray tube in this country as early as December, 1895, or January, 1896. Since Rontgen was professor in the University of Wiirzburg, Germany, it was quite natural that the apparatus makers of that country were among the first to produce X-ray tubes for export. Many such tubes came to this country but in a short time American
Uacuum Cubes. SINCE
the issue of the first cirular, describing X-Ray apparatus. many changes, impmvements and additions have been made. and the requirements of an X-Ray plant are now considerably greater than they were a year ago, and manufacturers of such apparatus are doing their best to meet all the demands of those interested by constantly improving the quality of their coils, static machines. fluorescent screens, etc, e t e For my part I have made the manufacture of the Vacuum or so-called Crook& Tubes a special study, and I think every one interested will agree with my statement that a feliahle tuhe is the most irnoortant factor in successful work. After a considerable time spent in experimenting,$ nave succeeded in making a tubs for which I can justly claim that it will give the least trouble of any at present in the market, which fact is attested by numerous letters of some of our mopt eminent exyeri. mentem and surgeons. There are different reasons why a tube will not always work satisfacto"ly, and the most important seems to be the varying resistance caused by slight changes in the Vacuum. Numerous suggestions and devices are constantly tried to regulate this defect, but so far they have not attained very permanent results The tubes of my make, however, which are of the focus type, as shown in cut. owe their efficiency and long life principally to the excellent qudity of the material used in their manufacture, to the correct size of the electrodes and their perfect shape, and last, hut not least, to their most careful exhaustion, which is done under my apeeizl supervision. For such, as desire. a tube, in which the Vacuum can he reduced if necessary, I have designed a tube, which has attached a bulh with a 3rd electrode, and by connecting the aluminum disc and the 3rd electrode only, and reversing the current or by slightly heating the attached bulh, the Vaevvm is lowered in very short time Tubes in which the Vacuum has become too low can be re-exhausted. provided they are in good condition otherwise, and if sent to me, charges should he prepaid bl
Froms 5
manufacturers were able to produce equally good tubes for about the same price. Importation decreased considerably, but not the importation of the necessary glass bulbs. Some of the American lamp manufacturers used lead-glass bulbs for the production of X-ray tubes but these were soon found to be less satisfactory than the German tubes which were made from a sodalime glass; therefore, large quantities of German bulbs made from the special soda-lime glass had to be imported. These bulbs varied in diameter from three to ten inches, the size most suitable for general purposes being the six-inch. The finished X-ray tube was similar to that shown in Figure 8 and was considered the standard tube for many years. Numerous modifications were introduced, two of the principal ones being a third electrode and an attachment for regulating the vacuum (see Figure 9). However, up to about 1910 the general appearance of X-ray tubes was similar to that illustrated. The electrodes 1 vsvally cany in stock 3 sizes; the large ones are particularly adapted to difficult surgical work wquiring a coil, giving at least 6' spark, for smaller work a medium tube for a coil of 4" to 6" spark will be found sufficient, and the small tubes will light up the fluorescent screen with a r' spark, and give good results with 4' of spark. I also make to order Vacuum Tubes according to special designs particularly for large and powerful induction coils, and solicit drawings for estimates on such work. The double focus tubes, as per cut shown below, are w e d ptincipallyon Tesla Coils where only the two concave aluminum discs are connected to the apparatus, and the double platinum disc in the middle left detached; however, when used with ordinary indoction coils, they are to be connected according to directions given in the circular sent with each tuhe. At this point I take the opportunity t o .mention that some manufacturers claim t o own patent rights on certain forms of Vacuvm Tubes, but without wishing to discuss details, 1 will state briefly;.that Vacvum Tubes of many different shapes, various degrees of exhaustion, and manifold designs as to the shape, material, and number. of electrodes, have been made for many years past, and the principles underlying the manufacture and forms of Vacvum Tubes have been so long ex: perimented upon by scientbts, that the right of any ,manufacturer to claim a royalty on Vacuum Tvber is rather doubtful. When ordering Vacuum Tuber, the mentioning,of style and make of coil or static machine used. also length of spark,;is very desirable, as I will be better able to select sumtable tubes. The prices of the Single Focus Tuber are:
58.00 . small.
-~
~edium.
580.00 - - ~. --
~rrge.
Double Fosur:
-
$15"
$,".OO
Rcgulrr,
Large
single Foeus with Auxiliary Bulb and 3d Electrode: $85.00
$,O.OO
Regular.
Large. I31
Frcune 6
were usually concave aluminum discs and flat platinum changes in the form and arrangement of the electrodes plates, generally attached to platinum wires sealed into as well as in the methods of evacuation. As the the glass. When American glass manufacturers were General Electric Research Laboratory, under the able to produce bulbs from a satisfactory soda-lime direction of W. Whitney and with the able assistance glass the importation of the glass bulbs ceased also. of Messrs. Coolidge and Langmuir, entered this field, During these early years evacuation was accomplished further development in the production of X-ray tubes by means of the various types of Sprengel, Geissler, and advanced from the hit-or-miss stage to more scientific Toepler pumps which were modified in many ways. methods. Most of this work is described in its successive stages One such modification by the-late Professor Boltwood may be cited as an example and is illustrated in Figures in the various journals devoted to radiology which, by that time, had become a special field of scientific as 10 and 11. In the meantime, the prowell as technical development. It is, therefore, unnecessary to go into various details which are now a duction of incandescent matter of common knowledge, and which are covered lamps was increasing to such in the catalogs of the present principal producers of an extent that speedier X-ray tubes and apparatus for their application. evacuation became important and rotary pumps made their appearance. Am the first models was so-called Gaede pump which had a porcelain housing porcelain displacement vanes. To the pumphead were a t tached steel intake and outlet tubes ground to a taper to make an air-tight junction with a corresponding ground-glass taper to which the bulbs or tubes to evacuated were sealed. These pumps ran in mercury and could be operated by hand or by a small electric motor belted to the flywheel (see Figure 12). However, this type of pump was soon replaced by one made of metal with the displacement mechanism running in oil. (Figure 13 shows one of the earliest types.) These rotary pumps worked much faster, needed less atFIGURE 7 tention and, of course, were less fragile than the glass mercury pumps which they superseded almost entirely in the production of incandescent lamps as well as X-ray tubes. Among the early manufacturers of X-ray tubes, who first used German glass bulbs and later bulbs blown in this country, were Swett & Lewis, Macalaster & Wiggin, Green & Bauer, E. Machlett & Son, Queen & Co., Victor X-Ray, as well as some individual glassblowers. But the production of X-ray tubes based on scientific research did not develop until about 1910 when Dr. W. D. Coolidge, of the Research Laboratory of the General Electric Co., announced a method of producing ductile tungsten. This material, owing to its high melting point and lower cost, largely displaced platinum for use in targets and resulted in various
IIowcver, the latest, and pcrhaps the most important impro\wntmt, 111 the production of X-ray tubes canlc about when borosilicate glasses of the Pyrex brand were substituted for soda-lime glasses. This cbanxe was a natural consequence of the development of modern high-voltage apparatus which must operate under very severe thermal conditions. Fate has placed the writer, who worked forty years ago on the first X-ray tubes in this country, on the staff 01 the Corning Glass Works where the bulbs used for the production of the present X-ray tubes are blown. The physical characteristics of Pyrex brand glassware, and especially its high resistance to thermal shock (due to the low expansion coefficient of this type of glass), have likewise made possible considerable improvement in the technic of evacuating X-ray tubes through the use of the so-called mercury diffusion pumps which are also made of Pyrex brand glass. Since pictures can tell more than words, a comuarison between the old mercury fall or lift pumps and the present mercuty vapor operatedin conjunction with an efficient rot&y oil pump, will give a better idea of the crude methods by which the old-timers had to work until scientific research showed the way to better results and more efficient operation. The apparatus shown on the cover of THISJOURNAL was probably one of the first outfits sold in this country. It would reveal the bones of the hand but was not capable of much beyond that. The Research Laboratory of the General Electric Co., where the development of ductile tungsten by Dr. Coolidge, the perfecting of the diffusion pump by Dr. Langmuir, as well as numerous other contributions to the making of better X-ray tubes were evolved, has been an outstanding factor in advancing the X-ray apparatus from the status of a novelty to that of one of the most important tools of science and industry. Today the production of X-ray tubes and apparatus rests in the hands of a few important firms who are able to maintain the exacting standards set up by the research laboratory, and the glassblofler who made X-
-
!
I,
ray tubes has been nearly eliminated from that field. The modem X-ray tube has to meet many diierent requirements for various purposes, so that even repairs on such tubes should be made in the laboratories of the manufacturers, where all facilities for final inspection and testing are available. The past forty years have witnessed many great developments due to scientific and technical progress, and while the X-ray apparatus. may not be a very prominent example from the finantial point of view, i t is perhaps one of the most useful for humanity.
SECTION C (CHEMISTRY), A. A. A. S. St. Louis Meeting, December 30, 1935, to January 4, 1936 The Wednesday afternoon (Jan. 1st) session will be abstracts of contributed papers intended for this held jointly with Section Q (Education) and will be meeting should be in the hands of the Secretary of the devoted to the second of a series of three symposia on Section, J. H. Simons, Pond Chemical Laboratory, the general relationships between the science of chem- State College, Pennsylvania, on or before November istry and education. The general subject of the sym- 23rd. The Thursday evening session, held jointly with the posium is "The Teaching of Chemistry"; R. A. Baker will preside. The names of the six symposium speak- St. Louis Section of the A. C. S., will be the occasion ers, and their individual topics, will appear in the of the address of the retiring Vice-president Joel H. Hildebrand of The University of California-"Dipole January number of THISJOURNAL. The Thursday morning and afternoon sessions will Attraction and Hydrogen Bond Formation in Their be devoted to contributed papers. Titles and short Relation to Solubility."
