X-RAY, VIOLET RAY AND OTHER RAYSCHAPTER IEVERYDAY USES OF X-RAYS
X-RAY, VIOLET RAY AND OTHER RAYS
To enumerate and describe all the practical uses of X-rays, apart from medicine and scientific research in general, would require a good many more pages than can be devoted to the subject here. To take a few cases at random, without describing the instruments and methods employed: radiography reveals flaws in the structure of iron and steel building and bridge materials, and in the cylinders of airplane engines, and so avoids accidents. In England a gasoline or petrol tank was shown to have rivet heads on the outside and none on the inside.
Serious defects in the steel axles of railway and automobile “under carriages” have been discovered by radiography. In one case, at least, the axles had been drilled in the wrong position and the holes had been simply filled with metal and covered over. An entire lot was rejected in consequence and probably serious accidents were forestalled.
“Cracks in castings, bad welds and weak places which do not show on the surface of metal are perfectly clear to the searching rays. How much would you give toknowthat that welded part in your automobile is really solid and perfect, that it contains no flaw to break down some day when you are twenty miles from a machine shop? A well-known mechanical engineer said recently that in ten years a metallurgical X-ray machine will be as vital a part of the equipment in an automobile repair shop, a foundry, or machine shop as it is now in a dentist’s office.”
“Cracks in castings, bad welds and weak places which do not show on the surface of metal are perfectly clear to the searching rays. How much would you give toknowthat that welded part in your automobile is really solid and perfect, that it contains no flaw to break down some day when you are twenty miles from a machine shop? A well-known mechanical engineer said recently that in ten years a metallurgical X-ray machine will be as vital a part of the equipment in an automobile repair shop, a foundry, or machine shop as it is now in a dentist’s office.”
We are assured byThe Iron Trade(73:26) that “the practice of analyzing metals by means of X-rays is only in its infancy. There is every reason to believe that soon great advances will be made in determining the crystallization and therefore the properties of metals. Students of metallurgy are well aware that the properties of metals and other bodies depend on the nature of their crystallization. The microscope has rendered valuable service largely because it enables the form and arrangement of the crystalline grains to be studied. The X-ray carries the same form of inquiry into a region 10,000 times more minute, thereby furnishing new evidence as to crystalline structures, so that it isnow possible to see the atoms and the molecules, and the way they form crystals. Every crystal has its characteristic X-ray spectrum and can be identified thereby even when the individual crystals are beyond the resolving power of the microscope and the substance is in danger of being called amorphous. If a specimen contains a mixture of crystalline substances, the spectrum shows the combined effect of all the substances, and provided each individual spectrum is known, the specimen can be analyzed.”
The X-rays are also used to determine the quality of the fabric in automobile tires, and even to detect irregularities in the centers of golf balls, and to reveal why some of them fly straighter and farther than others.
“The professional detective, too,” says Mr. Wilfred S. Ogden (Popular Science Monthly, August, 1923), “will find X-rays useful in his business. Consider the detection of infernal machines, for example. Two or three X-ray plates will tell an investigator just what is in a suspicious-looking box. If it is a bomb the X-ray will show him how to get it apart and render it harmless. Immediate detection of false bottoms in trunks is child’s play with the X-ray. When the government provided itscustoms inspectors with X-ray machines the gems which smugglers try to hide in the linings of clothes or in hollow-handled hairbrushes might as well be worn openly.
“The X-rays give us one of the easiest ways to detect the alteration of checks and other documents. It is seldom that such an alteration is made with exactly the same ink used on the original. Inks even of the same color, differ in the way they affect the rays. In most cases all that is necessary to detect an alteration is to place the suspected document for a moment under the X-rays and make a photograph of it. The new ink used in the alteration will stand out clearly as different from the old.
“The industrial detective will find X-rays just as useful. The adulteration of foods by sawdust, sand or clay; the adding of too much filler to paper; the presence of grit in lubricating oil, all will be revealed.
“Another use of the rays comes home to every cook and housewife. X-rays constitute the only sure way to tell good eggs from bad. Pass each egg in turn through the X-rays and let its shadow fall on a chemical screen. You will see exactly what is inside each egg. Theones containing hopeful chicks may be rejected.”
One of the most remarkable economic or biological uses of the X-ray so far developed is the study of silk-worms and their diseases. The Silk Association of America has established a laboratory—Department of Sericulture—in the Canton Christian College, presided over by a staff of Chinese and foreign entomologists. Here the silk-worm is X-rayed by powerful microscopes, and all his disorders diagnosed and corrected, says Mr. Philip A. Yountz (Scientific American, September, 1925).
“Numerous autopsies on deceased members of the silk-worm tribe revealed that from 50 to 100 percent of the worms raised in South China were infected with diseases that made the infant mortality rate excessively high and destroyed the value of the silk from those hardy enough to survive. The elimination of these diseases would enable South China to produce four or five times as much silk.”
In Great Britain, X-rays are used in the analysis of coal, the method being an adaptation of the X-ray stereoscope.
In Berlin, S. Nalken, a noted criminologist, has devised an important improvement in finger-print identification. X-ray pictures are obtainedof the finger, with the muscles and bones. This is done without the use of any chemicals that could obstruct the delicate furrows of the finger lines. Moreover, the finger bone is shaped so characteristically as to aid identification. Whenever a certain likeness of finger-lines is discovered, the bones are examined to see if further research is necessary.
Picture fakers have been dethroned by application of the X-ray to paintings. Recently painted “old masters” are now easily detected. Modern artists use white-lead, which is more opaque than the “priming” or “sizing” used by the older artists; and the X-ray device “made in Germany” in 1914 by Dr. Faber, and further developed by the French expert, Dr. André Chéron, at once distinguishes the old from the new. One picture by Van Ostade, of men drinking at a table, proved to be a fraud when submitted to the X-ray; it had been painted over a study of dead birds. Another, called “The Royal Child,” a supposed 16th century work, now in the Louvre, was proved to have been painted during the 19th century over a picture of very much earlier date.
During a popular lecture on the X-ray in London, before the Royal Institution, the distinguished physicist, Prof. G. W. C. Kaye,showed a number of radiograph slides, among which were two pictures by Dutch painters, one representing the Madonna and the other the Crucifixion. In the former, the Madonna appeared to be looking at something which was non-existent in the canvas, and a radiograph proved the missing object was a child which some former owner of the picture had painted out. In the second picture, a woman in the attitude of prayer was found to have been painted over what was in the original the figure of a man in monk’s garb.
The first X-ray pictures ever taken of a mummy were completed by scientists at the American Museum of Natural History, New York City. The pictures showing the skeleton in detail are expected to be a great aid in studying the development of bone formations in the evolution of man. This first subject of the scientists’ X-ray was a South American Indian mummy. Fake mummies, like false gems, are instantly detected by X-ray methods.
One of the methods used for detecting the theft of diamonds at the mines is to examine the workmen with X-rays. Of course, a fluoroscope is used to make the X-ray image visible, and this is the type used in any regular X-ray work.
The X-rays are now being used in shoe-stores—“foot-o-scope” instruments—to enable shoe salesmen to see the bones of a customer’s foot and thus make correct fittings of shoes.
A few years ago there arrived from Germany a new kind of mechanical doll. “A secret mechanism inside enabled it to walk, sit down or stand up, and to do other unusual things. The importer in possession of the sample doll would not allow it to be opened. But one of the competitors borrowed the doll. He had promised not to open it. But he made some X-ray photographs of it. Now he is manufacturing these dolls himself.”
During the World War every effort was made to introduce contraband materials into Germany and if it had not been for the all-seeing eye of the Roentgen ray, it would have been impossible to prevent materials of the utmost importance to the enemy from reaching him by way of neutral countries. Efforts were made repeatedly to smuggle rubber and copper by burying them in bales or bundles of other materials. It would have been impossible to have made a minute investigation of every bale that was shipped, but by means of X-rays it was possible to see through these bundles and packages and locate any substances that were more or less opaque to the rays.
The X-ray has been found useful for examining timber up to 18 inches thick for internal knots, resin pockets, cracks and other defects.
“When submarines were active and the supply of the best kinds of wood was uncertain, it was necessary to make some of the wooden parts out of small pieces of ordinary wood fitted and glued together. The way these pieces were joined and fastened was extremely important. A bit of weak glue inside some little strut might mean a disastrous collapse in the air. But real inspection seemed impossible, for the places where important faults might exist were hidden from view. Finally scientists solved the problem by building an X-ray apparatus with which they could look into the inside of each built-up airplane part and tell whether it held some little imperfection which might prove dangerous.
“This ‘internal inspection’ of wooden articles by X-ray has been applied, since the war, to many other articles. Hidden joints inside high-class furniture and cabinet work, invisible knots and flaws inside the wood itself, can be determined easily by X-ray examination.” (W. S. Ogden).
The Scientific American(September, 1924) published an abstract of a paper read beforetheDeutschen Bunsen-Gesellschaft, in which Dr. D. Coster showed that “the relations between the X-ray spectra of the different elements are so simple that, in some respects, they are more useful for purposes of chemical analysis than ordinary luminous spectra. An important advantage is the fact that the X-ray spectrum of an element is quite independent of the nature of the compound containing it. It is easy to detect the presence in a mixture of which not more than one milligram is available. Certain precautions are necessary in examining the X-ray spectra; although the number of lines for each element is comparatively limited, recent observations have shown the existence of a number of weaker lines; in addition to this, with the high voltages now generally used, not only the spectrum of the first order, but also those of higher orders appear. Slight impurities in the material of the anticathode, and in the subject under examination, also give their lines, so that there are often various possibilities to be considered before a given line can be explained. Not only the wave length, but also the typical appearance of the suspected lines must be considered, as well as their relative intensity. By measuring photometrically the intensity of the spectral lines it is possible, in some cases, to obtaina quantitative estimate of the amount of an element present in a mixture.”
Another method of rapid analysis of material in the laboratory by the use of X-rays in a much shorter time than that required by the older chemical methods is that devised by Professor Urbain, of the Minero-Chemical Laboratory at the Sorbonne, with the assistance of Eugene Delaunay. Mr. Delaunay, who did the actual work of testing the new X-ray method, says there is no risk of error.
By employment of X-rays the scientist is now able to ascertain the arrangement of the atoms and molecules within the crystal “network” (structure—or “space lattice” of the crystal).[1]The results are obtained from the study of the reflection and refraction of the rays by the crystals, or, more precisely, the successive rows of molecules in the crystal. These act toward the extremely short X-rays in the same way as a grating spectroscope does to ordinary light-rays.
Man’s ability to lengthen the ultra-violet end of the spectrum is limited by his capacity toprovide a diffraction grating, or a mineral prism, which can split up light-waves of increasingly greater frequency (or shortness). The width of a grating space (a fine line on speculum metal, which acts as a minute mirror) must be comparable to the wave length of the light. Previous to the discoveries of Prof. Max von Laue in Munich (now in Zurich), and Prof. William Henry Bragg, of the University of London, no grating or other material was known whose spaces were as small as the wave length of X-rays. Laue conceived the brilliant idea that the regular arrangement of the atoms in a crystal might serve the purpose. They did. Bragg, and later his son, Prof. W. L. Bragg, of the University of Manchester, followed up the work of Laue with results of immeasurable value to science.
A very important relation between the atomic number of an element and its X-ray spectrum was discovered by the brilliant young English physicist, H. G. T. Moseley (1888-1915), in his 26th year, a year before his death by a Turkish bullet at the Dardanelles. While analyzing the characteristic X-rays which are given off when any kind of substance is bombarded with cathode rays, Moseley found that the atoms of all the different substances emit radiations orgroups of radiations which are extraordinarily similar, but which differ in their wave lengths as we proceed from substance to substance; the frequencies (wave lengths) change by definite steps as one progresses from elements of lower to elements of higher atomic weights. Through Moseley’s epoch-making discovery we now know that each of the 92 elements, from hydrogen to uranium, is built up by successive additions of one positive charge (proton) and one negative electron, and that the atomic numbers—from 1 to 92—correspond to the number of protons and electrons in each successively heavier (and more complex) atom.
FOOTNOTES:[1]This phase of our subject can only be alluded to in this little book. For an authoritative yet easily understood exposition of the subject, see Bragg, W. H. and W. L., “X-Rays and Crystal Structure”; also Kaye, G. W. C., “X-Rays”; and, for more advanced reading, deBroglie, Maurice, “X-Rays”.
[1]This phase of our subject can only be alluded to in this little book. For an authoritative yet easily understood exposition of the subject, see Bragg, W. H. and W. L., “X-Rays and Crystal Structure”; also Kaye, G. W. C., “X-Rays”; and, for more advanced reading, deBroglie, Maurice, “X-Rays”.
[1]This phase of our subject can only be alluded to in this little book. For an authoritative yet easily understood exposition of the subject, see Bragg, W. H. and W. L., “X-Rays and Crystal Structure”; also Kaye, G. W. C., “X-Rays”; and, for more advanced reading, deBroglie, Maurice, “X-Rays”.