Fluorochemistry in Military Science JACK DE MENT Couch Building, Portland, Oregon VERY war, since the dawn of mankind, has been marked by the introduction of devices and knowledge which were unknown or overlooked during peacetime. The maintenance of our national defense and the preservation of our internal security have shown us that it is, at times, very profitable to employ certain highly specialized branches of science to achieve that end toward which we are all looking. In the present situation this is especially true of certain aspects of fluorescence and ultraviolet light. These agents have made possible many remarkable advances in nearly every phase of warfare art, science, and industry, and their utility will continue to grow and be appreciated after hostilities cease. Indeed, it has most aptly been said that a nation's scientific activities are not mere national property; they are international possessions, for the joy and service of the whole world. It is during war that nations hold them in trust for humanity.
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Phosphorescence, however, is the process in which light emission may continue for seconds, minutes, hours, or even weeks after the source of energy has been taken away. The outstanding distinction between the two is of course in the duration of luminescence and the lag which occurs between removal of the radiation and the cessation of light release. Both fluorescence and phosphorescence are generally believed to be identical, except for this characteristic, and both are adequately explained on the basis of the same theory. The distinction between the two is therefore phenomenological and historical rather than scientific. Fluorescence is ordinarily classified according to the nature of its exciting agent, and a term is adopted which connotates the form of energy which has been employed to produce light emission. The type of excitant most used is ultraviolet light, usually of two kinds suitably filtered so as to eliminate objectionable visible light which might exert a masking effect on the luminescence. One wave length is most effective, in general, FLUOROCHEMISTRY for exciting fluorescence in organic substances, and i t is The modern scientific history of fluorescence began called long wave length radiation. The tentative with the work of Sir George Gabriel Stokes (I)in 1852, standard for long wave length radiation is the convenalthough fragmentary knowledge about luminescence iently situated gamut of energy a t 3650 A.U. Short was known for many years previous to this time. wave length ultraviolet light is usually suited for the During the last several decades the development in excitation of inorganic substances and its tentative knowledge and use of fluorescence entirely overshadows standard lies a t 2537 A.U. Both kinds of radiation practically all earlier investigations in the field. A are given out in substantial amounts by incandescing clearer interpretation of the phenomenon of lumines- mercury vapor under the proper temperature, prescence has been brought about by receut advances in sure, and voltage conditions. There are many sources of ultraviolet light, all of chemistry and physics: it is becoming widely appreciated because of the large number of industrial and which have more or less value for fluorochemical studies. There has been a great deal written upon scientific problems which can be solved by its means. Fluorochemistry is the name recently given to the this one aspect of the science, and as i t is beyond the physicochemical science which embraces the theory and scope of the present discussion interested readers are utility of fluorescence, phosphorescence, and radiation encouraged to consult special works listed in the (2). The basic phenomenon of fluorochemistry is bibliography for more detailed information ( 3 , 4 , 9,13). fluorescence, the emission of light, usually visible, but It is to be understood that none of the ultraviolet not always, from matter under the influence of an ex- filters in general use today is capable of entirely elimiciting agent. Fluorescence is a complicated physical nating all visihle wave lengths. All permit a small process by which energy is absorbed within atoms and amount of purple and blue to pass, hut this is not obmolecules, raising them to an upper level which quickly jectionable for most ordinary applications. It may also returns to its ground state with the simultaneous re- he pointed out that research isnow in progress on plastic lease of light. Fluorescence is distinguished from lumi- filters which will be superior to glass filters, possessing nescence due to incandescent heat, or candolumines- the desired transmission characteristics, heat resistidty, cence, in that it is virtually a "cold" process; hence, high mechanical strength, and low cost. the use of the term "cold light" ( 3 ) . I t is in this connection that an interesting incident For a long time there has been considerable confusion occurred in England during the first world war. Major in regard to the diierence between fluorescence and R. W. Wood, Professor of Experimental Physics at phosphorescence. Fluorescence is usually defined as Johns Hopkins University, was visiting centers of light emission lasting only as long as the luminescent military intelligence and upon inquiring as to the nasystem is under the influence of an exciting agent, ture of work a t one laboratory was told that a device ceasing the instant the source of energy is taken away. of the utmost secrecy was being employed. The Eng116
lish Army men were astonished when Major Wood asked them whether or not the device was an ultraviolet light unit. After a hasty conference with their officers the Major was let into the laboratory. The men were much chagrined when Major Wood commented: "Why I invented that filter and sent it to your offices over a year ago!" (5). Excitingagentsneednot beultraviolet light, although it is in this form that energy is most efficaciouslyintroduced into matter. Fluorescence and phosphorescence can be brought about by visible light (photoluminescence), x-rays, electrical waves (electroluminescence), the radiations from radioelements (radioluminescence), electrons from various natural and artificial sources (electronoluminescence or cathodoluminescence),sound waves (sonoluminescence), neutrons (neutronoluminescence), and by a number of other atomic and subatomic particles. In addition, there are several ways in which light emission is more or less indirectly brought about. Thus, friction (triboluminescence), crystallization (crystalloluminescence), low temperature heat (thermoluminescence),and oxidation or other special chemical reactions (bio- and chemiluminescence), may enter into the process. For the higher energied excitants luminescence is the direct result of the excitation of the atom or molecule. But for the lower energied excitants, such as in the case of crystallization and low-temperature heat, light emission is explained on the basis of a previous radiation history, this type of excitant merely serving as a key to unlock the stored energy. There are a number of other ways in which luminescent processes, and luminescence itself, are classified and so rendered that relationships between the various types of processes can be developed. One interesting distinction lies in the dserences in the intensity of the luminescence. When the light is characteristic and bright, so that its features are unmistakable to the unaided eye, it is spoken of as macroluminescence. Most of the present-day industrial value of fluorochemistry centers about macroluminescence. However, there is an indeed significant form of microluminescence in which the emission is so feeble, consisting of so few quanta, that it can only be studied by instruments such as the Geiger counter and the high sensitivity photocell. When an acid is mixed with a base, or when certain somewhat simple chemical reactions occur, light may be emitted as chemiluminescence: the more familiar of these processes, however, entails reaction between complex organic substances, such as 3-aminophthalhydrazide, but in the simpler instances there may be a light emission whose wave lengths extend down to 2000 A.U. or less. This rather astonishing phenomenon leads to many new concepts in chemical and physical science of great implication (6). While fluorescence and phosphorescence are most familiarly known because they emit visible light, this does not mean that luminescence cannot be made up of wave lengths above or below the visible range. Ultraluminescence, or light emission consisting of wave
lengths less than 3950 A.U. is a widespread property of matter. Gamma rays, and high speed electrons, induce in water a luminescence which extends down to 2500 A.U. This continuous and rather intense emission is believed to extend to the shortest wave lengths of ultraviolet which are transmitted by water. This ultraluminescence of water is richer in short wave lengths than is the radiation from a 0.5-watt iucandescent lamp (4, 13). Hundreds of other substances will emit ultraviolet light when subjected to cathode rays. The n-paraffins, containing from 1to 8 carbon atoms in their chains, emit wave lengths as low as this and in greater intensity. Paraffin oil and nujol are among the more familiar substances which have an intense ultraluminescence (4). Infraluminescence is light emission consisting for the most part or entirely of radiation lying above 7500 A.U. Much less is known about infraluminescence than ultraluminescence; the energy relationships involved in an ultraluminescent process are much greater than those in infraluminescence, so rendering the former mechanism more easily studied. One of the present implications which infraluminescence has for physical and chemical science in general is in explaining the nature and degradation of thermal radiation in systems of noncollidingparticles (4). Fluorescence is a characteristic of many substances, and in certain materials it is highly variable, dependmg upon the nature, purity, history, type of exciting agent, and the condition of the specimen. This makes possible a branch of analytic science known as fluoroche~.ical analysis. Many substances luminesce strongly and characteristically when they contain a trace of impurity and especially when they have a crystalline structure which so enables the formation of energy levels. When the luminescence of a substance can be closely associated with the presence of an impurity, the luminescent system is called a phosphor. If the luminescent system is highly purified, but shows structural discrepancies which allow the existence of energy levels not normally present the system is called a quasiphosphor. For a long time confusion has existed in fluorochemistry in regard to the fluorescence of highy purified inorganic solids, but it is now known that many such substances are in reality quasiphosphors; this, however, does not mean that a pure substance cannot luminesce. Solid phosphors are divided into the manoactivated and the miaoactivated. The trace impurity is termed the activator and its action in a structure is that of a luminescence center. Microactivated phosphors are most well known, usually having avery small amount of metallic trace in a preponderance of bulk material. Many of our best analytical grade reagents are actually microactivated phosphors,for activation maybe brought about by quantities of impurity well below the threshold of the best methods of purification. In the microactivated phosphor light emission is very often characteristic of an atom or ion. In the macroactivated phosphor there may not be too great a difference in concentration of activator and bulkmaterial or base. Mac-
roactivated phosphors frequently have the common property of emitting light characteristic of unbroken molecules, for a macroactivated phosphor may contain as much as 40 mole per cent of a compound in solid solution with a related compound, forming a system which is called quasichemical,since it does not conform to the usual rules of stoichiometry. These simple distinctions are obviously of both practical and theoretical importance. Approximately 200 mineral species fluoresce characteristically with ultraviolet light of various wave lengths. An additional 100 species present an appearance which is semicharacteristic. Many fluorescent minerals vary greatly in their response to radiation, but in a good number the fluorescence is sufficientlyreliable to allow very positive identification by mere observation under an ultraviolet lamp. Specimens of the same species from the same locality may vary widely in shade of fluorescence, or in intensity, or some may be practically nonfluorescent. Many organic chemicals fluoresce brightly and characteristically, alterations in emission frequently being produced by solution changes, concentration and temperature, exciting wave length, purity, and many other factors. The color of fluorescence of an organic compound may change entirely after it is placed in solution. For example, solid riboflavin is excited to a bright, deep orange by 3650 A.U. light, but in water a strong green to green-yellow fluorescence is seen. The bright fluorescence of organic chemicals is due in certain cases to a phosphor-like system. Thebrilliant green glow of impure anthracene is caused by the activating action of small amounts of *sene in the structure, pure anthracene exhibiting a blue fluorescence, and some investigations have shown that this may even be violet after exhaustive purification. The fluorescence of metal-organic compounds as a class has not been widely studied, although a great deal is known about the luminescence of metal-organic dyestuffs. Many metal-organic compounds fluoresce brilliantly and characteristically, and in certain instances the presence of metallic impurities, such as iron, exerts a quenching or extinguishing effect upon their luminescence. In other compounds the fluorescence is shifted in wave length because of the cation, this being especially evident in metallic stearates. The presence of an alkali or alkaline earth element cation in a complex organic structure may determine the difference between a remarkably brilliant luminescence and substantial nonfluorescence. Calcium theobromine salicylate is a good illustration of a brilliantly emitting substance in which the make-up is more favorable for greater quantum yields than in either theobromine or salicylic acid alone. In general, the fluorescence of inorganic compounds is not as distinctive as that of organic compounds. The fluorescence of inorganic compounds is influenced by a great many factors, and a t present workers in fluorochemistry are not in complete agreement as to all the causes and the relative weight which is carried by
each: in fact some workers disdain lookimg upon pure inorganic substances as being fluorescent, although this can indeed be proved erroneous in both experiment and theory. Cathodoluminescence is a property of matter as such, and is not always a by-effect attendant with anomalies in structure and composition. The fluorescence of pure inorganic substances is, in general, of less intensity than that of organic compounds, and it is influenced by such factors as particle size, water content, crystallimity, previous radiation history, impurities, and numerous others. When inorganic substances are to he purified for use in lightmg tubes the best grade reagents must be employed as raw material, and all operations carried out with extreme precaution: phosphors are manufactured and studied in special air conditioned laboratories designed for this purpose, as even slight particles of dust floating in the air may change the product. Iron or steel buttons, suspender clips, keys, and so on, must not be worn when high grade phosphors are being manufactured, for the slightest trace of iron in many phosphors will render the product unsatisfactory (7). NEW WARFARE OPTICS
In describing the applications of fluorescence and ultraviolet light to military science, the writer must necessarily limit himself to facts and techniques generally known or available to chemists and physicists throughout the world. The remainder can be left to the imagination of the reader, for certain of the uses of fluorochemical knowledge are so spectacular that they exceed the most vivid imagination (8). The extent of the application and values of fluorochemistry in warfare may be noted by citing some of its more recent utilities in industry and science. For example, a small globule of mercury metal can be held in the hand, and by use of a source of short wave length ultraviolet light, its image may be projected upon a screen coated with a phosphor. At room temperature the mercury evaporates appreciably, giving off fumes which cast a dark shadow on the screen because of their opacity to the ultraviolet. This one simple method has enabled prospectors to go into the field and search out large bodies of mercury ore, thus reinforcing present sources of the metal so essential in the manufacture of mercury fulminate. Within the last year the methods of fluorochemistry made possible the discovery of the largest body of tungsten ore in continental United States. Scheelite and powellite, two important tungsten sources, both luminesce strongly with 2537 A.U. ultraviolet light, and it is now possible for an untrained operator to make close determinations of the molybdenum content of ore, thereby expediting progress in this field. It has very truly been stated that this one method has been the most revolutionary discovery in tungsten technology within the last several decades (9). The detection of petroleum in shale and sand, and the detection and recognition of rare minerals, is possible by their fluorescence. All of these have a direct bearing
agent. Fluorescent paints and chemicals may be applied to many objects to provide a means for people to find their way about in semidarkness. Paper, cloth, wood, metal, plastics, and many other materials can be so treated, and parts of clothing, curbon the ultimate consequence of the war by the exceed- ings, stairways, moving vehicles, and permanent obingly valuable background of know-how they provide jects of almost any kind can be rendered sufficiently for industries and sciences supplying the armed farces. luminescent in the dark, either permanently or tempoMany other examples are known, any of which may be rarily, so that they can be seen. There are two ways in of a like order of importance in a war effort, but most in- which the luminescence is excited: (1) a small argon terest centers about the applications of luminescence bulb or other source of low intensity ultraviolet light and radiation in any type of active warfare: the real may be mounted nearby so that its radiations strike the story to be told must remain until after hostilities luminescent pigment and render it luminous and (2) cease, but in the following details an idea will be ob- the luminescent preparation may contain a small tained as to the large number and wide variety of fields amount of radioactive element which serves constantly to which the new warfare optics may be applied. to excite the substance. Each has its limitations and General Warfare Uses. Several hundred uses of values depending upon the given use. In the illuminafluorescence have already developed in regard to the tion of airplane instrument panels during the first world special type of illumination needed in a blackout. war the self-excited phosphors were widely employed, Whereas fluorescent light provides that low order of but today it has been found that best results are obbrightness which is so necessary to conform to the r e tained by using an external source of ultraviolet light. stricted light conditions of a blackout, a great deal of Thus, present-day instrument panels have their dial overpopularization has exaggerated the efficacy of this figures made from luminescent plastic or coated with a
U.S.Army Air CorPs Photo
EQUIPMENT POR LIGHTINGARMY-AIRPLANE INSTRUMENT PANELS. THE INVERTER(AT TOP) CHANGESD.C. BATTERY CURRENT INTO 110 V. A.C. FOR %UORESCENT LIGHTING SYSTEM.FIXED FLUORBSCENT ASSEMBLY AT RIGI~T.FLEXIBLE UNIT WHICHPILOTCANMOVEAT BOTTOM
close of the first world war, in 1919, R. W. Wood made a complete disclosure of the method of using high intensity ultraviolet light as beacons and for secret signals during wartime (11). Several patents have also been granted on this subject in recent years. Trench signaling, and intertank and intercar signaling can employ this form of invisible communication with considerable advantage. The low order of brightness of the fluorescent receiver prevents detection by enemy units working close by. These are just a few of the many possible variants of the principle. Ordinary lubricating oil, vaseline, and similar materials often fluoresce with a bright blue or green color in ultraviolet light. This makes possible an unusual method of communication by friendly agents in enemy territory to tanks invading a t night. Large arrows or markers can be made in the middle of a road, even in the presence of the enemy without creating suspicion, to be picked up later by tanks and troops equipped with ultraviolet light units. Fluorescent dyes and chemicals can be employed as an aid in maintaining a military caravan intact during night operations. A fluorescent substance placed on the highway or terrain, by the leader of the column, can be of obvious advantage to those who follow, since there is no sound created in the communication and no very evident trace left. A change in the color of a fluorescent substance serves to convey information without the use of the radio. Small fragments of fluorescent paper may be used as a substitute for liquids or bulky solids. Trees, rocks, buildings, and other objects can also be marked in this fashion. Signaling to Aircraft. Aircraft operating over water are usually provided with rubber life rafts: many of the present rafts are equipped with a small tin of uranin powder or solution which is released upon idation or a t will at any later time. The bright yellow-green fluorescence which spreads over the water renders the life raft much more visible from the air, since bright sunlight is all that is needed to excite the luminescence. Kircraft flying at a distance can usually note the fluorescent spot before the raft becomes visible, and this method has already been responsible for saving a number of lives. However, certain faults have arisen in this method and one possible remedy has been to change the nature of the solution so that those on the raft are assured a greater chance of being rescued. A solution has been developed it1 which the uranin or sodium fluoresceinate, is dissolved in a special base. When this is released upon the water it immediately spreads over an enormous area, much like the oil from a sunken ship. The composition of the film is such that it remains intact in rough sea, maintains a more favorable pH so the fluorescence is at an optimum brightness, and prevents the formation of globules of dye which sink undispersed c a n r i ~ a aP ~ O ~ O (12). UNDERULTRAVIOLET LIGHTFLUORESCENT LACQUER-ENAMELSThe uranin signal is not restricted to life raft use GLOWRRILLIANTLY TO TRANSFORM A PROCESSING MILLUSEDIN as well as life boats alone: individual life THEIR~ ~ N U F A C T L ' R E INTO A RADIANTLY BEAUTIFUL RIVEROF may be equipped with flasks of the dye. In arctic LIGHT fluorescentpaint. 4 special converter has been built so that battery current can be changed into 110 volts a. c. Such lamps are mounted on a flexible neck and can be moved in any direction, proving valuable for reading maps in the dark or for referring to luminescent instrument dials. Police science and criminology are both profitable fields from which to draw experience and knowledge about the values of ultraviolet light for warfare science: many aspects of these fields are very closely related. The criminologist who has turned military scientist has a t his disposal a sharp weapon when his previous experience and work have included fluorescence and ultraviolet light. As might be expected, the complement of weapons and methods employed by the criminal are not distantly related to those used by the saboteur and counteragent. One of the greatest hazards in the manufacture of explosives is static electricity generated on a moving rubber belt or some part of a machine. The real hazard lies in the possibility of a sparkover which can and sometimes does cause an explosion. In the petroleum industry where highly inflammable substances are being refined this presents a considerable hazard. The strong ionization caused by short wave length ultraviolet light passing through air provides a certain remedial value, since any accumulation of electricity may be dissipated before it has a chance to spark (10). Signaling. As ultraviolet light is invisible, it can be used for secret signaling a t night or in the daytime. Of the many ideas which have been suggested, nearly all embrace the simple principle that the sender project an intense beam of filtered ultraviolet light toward the receiver, who interprets the result by means of a fluorescent screen, luminescent binocular reticle, or photocell. This was thought of during the first world war, and i t remains essentially the same today, except for minor im~rovisationsand ~erfections. In fact. iust after the
operation the uranin shows very brightly against a white background of snow. Parachute fabric can also be dyed with the substance so that it is rendered more visible from both the ground and the air. In this way individuals who are separated may more easily find one another, and their equipment may be more easily located. Fabric dyed with a luminescent dyestuff can he used for signaling to aircraft in jungle regions, where it shows very well against a green background, in the arctics, and on the desert. Aircraft Detection and Location. The extinguishing or quenching of phosphorescing screens by infrared rays has many military possibilities, but as yet only experimental use of this fact seems to have been made. An apparatus has been developed which depends upon the quenching of a phosphorescing screen of zinc sulfide. Infrared radiation is emitted more or less by all hot objects, hence aircraft and auto engines may be detected a t a distance by equipment relying upon this principle. However, a number of interfering factors must be considered in the application of this fact, and its development for widespread use is far from easy. When used in conjunction with a photocell, a system can be constructed to aid in directing antiaircraft and antitank gun fire (9). The electrical device which enables pilots to detect other planes in the darkness by their infrared radiations is called the "A-eye." In operation, two screens are mounted on the night fighter aircraft, one screen being sensitive to infrared whereas the other is responsive to ultraviolet. When the infrared from an enemy plane engine strikes one screen it emits a stream of electrons. The electron image, in turn, is revealed upon the second screen coated with a luminescent substance. The principle, despite the hare facts which can be ohtained a t present, appears to be similar to the luminescence of a fluoroscopic screen under x-rays. Accessory equipment enables the pilot to direct gun fire in an effective manner. Small marine craft and airplanes can orient themselves with infrared devices when the radiations are directed from a fixed station. Military Intelligence. The importance of invisible writing and secret messages has long been recognized in military intelligence. One of the reasons such methods are lookzd upon with favor by those who use them is that message-writing based on new technique with little-known inks, papers, or developing agents allows the agent to keep one jump ahead of the counteragent. Should the procedure employed by the enemy for detecting and inspecting documents be revealed, it hecomes a rather simple matter to devise a process which will escape detection and attention for a t least a short time. Fluorescent inks and writing media are of an almost infinite number and very wide variety. For example, one laboratory which specializes in fluorochemical study has a t its disposal a master file of over 5000 different luminescent substances, all perhaps of potential value for secret writing (13). The simplest ink, however, is water, milk, urine, or other common liquid
which leaves a characteristic marking on ordinary or special paper or cloth, but which presents a fluorescence under an ultraviolet lamp. In one prison an inmate used urine and milk to write messages for some time before his methods were revealed. More refined operators employ solutions of chemicals which glow brightly under ultraviolet light after being treated with one or more chemical reagents and heat. Some chemicals do not fluoresce appreciably until treated with a chemical reagent, and when the reaction involved is highly selective it may be most difficult to detect the writing. One of the cleverest message-writing techniques is based upon the excitation of fluorescence by a small range of specific wave lengths outside the ordinary gamut emitted by the usual light sources. Certain phosphors have been prepared which respond selectively to certain wave lengths, although other types of radiation fail to evoke any visible luminescence. It is possible in prison camps or under other adverse circumstances to devise both filter and light source so that messages may be read or written. A single thickness of purple cellophane passes enough ultraviolet from an ordinary incandescent lamp or from the sun, and lubricating oil, vaseline, egg white, butter, meat fat, sweat, urine, or other material can he employed as the writing medium. An idea of the delicacy of facts pertinent to intelligence work may be had when it is realized that it is often possible to tell whether or not a person has been kissed and rubbed the lipstick off, held or drunk a cup of coffee, or handled or contacted greasy objects of any kind. On many solids, merely writing with a blunt object, without leaving any visible mark, will suffice for communication which is revealed under ultraviolet light. Waxes and oleaginous substances are satisfactory for this purpose. Pressure marks left on the surface of paraffin or waxed shoes or leather goods can be revealed with little difficulty under ultraviolet light, although they may be entirely invisible in white light. In paraffin a purplish colored fluorescence is observed a t the points of contact, these showing against a blue fluorescing background. In a similar fashion, invisible scratches made on wood, stone, fingernail, and sometimes skin, can berevealed. For bringing out markings on paper which may have been made by water, pressure, or other means which are likely to be evanescent, the document may be painted on the opposite side with a solution of anthracene. After drying, the markings may be traced against the strongly fluorescing background. As a substitute for anthracene, various other substances may be employed, using instead, such materials as petrolatum and lubricating oil. Moreover, the appearance of papers arid textiles in ultraviolet light is sometimes changed after chewing or tearing. Paper can he torn in but a few ways, and an experienced counteragent can study the specimen fragments and often get an insight asto themethodof tearing. After chewing, saliva produces stains which are visible in ultraviolet light.
conti-GI0 Pholo
THISFLUORESCENT MARKING IS INVISIBLE IN ORDINARY LIGHT. REQUIRINGULTRAVIOLET LIGHTTO BRINOIT OUT
Identij'ication and Marking. Fluorescent chemicals may be used for many types of markmg and identification. With suitable modification they can be adopted for use on humans as well as upon other objects. The marks are invisible in ordinary light and are not necessarily rendered visible by the ordinary chemical and physical treatment employed to develop such agents. Persons can be branded silently and harmlessly by objects which have been dusted with invisible coatings of fluorescent powders. The insoluble phosphors can be efIicaciously employed since they are often unaffected by soap and water and by ordinary chemical reagents. These inert powders fluoresce brightly and are inconspicuous when placed on merchandise, tools, paper, money, or other persons. Tattooing has long been a means of markmg the skin. Most of the objection to the tattoo is, of course, the visibility and permanency of the markings. Tattooing has been employed as a tool for marking persons with serum sensitivity or with diseases such as diabetes or epilepsy. For noting blood group and for placing a warning code that an individual may respond unfavorably to certain therapeutic agents, tattooing is of limited applicability. Fluorochemistry, however, has given rise to an invisible form of tattooing which, though yet in the experimental stages, may solve many of the problems in the development of a permanent marking technique (14). It depends upon the use of inert and insoluble phosphors which respond to x-rays or other radiation. A method has already been perfected in the laboratory of the writer whereby special phosphors can be impregnated in the skin by the tattooing needle, remaining invisible to the naked eye, but being easily brought out with x-rays. This invisible tattooing is now being developed so that an ordinary ultraviolet lamp can be employed for rendering the marking visible. The New York State Department of Health has suggested that these invisible tattoo marks may aid in the identification of soldiers killed in future wars. The department of correction has also published the information that the method might be used to brand hahit-
ual criminals or sex offenders. Mark'mgs might also be used near surgical scars to enable a physician to determine accurately the case history of a patient without relying on his statements. Gas Mask Testing. Some of the diiculties encountered in testing gas masks are well known to many people. These devices must be made gas- and vaportight, and the most rapid and effective way of detecting leaks often presents a problem, especially when mass production is involved. The writer has developed a method which entails the use of flnorescent chemicals and ultraviolet light (15). Briefly, in testing the efficacy of a new mask, very finely powdered anthracene or other fluorescent chemical is allowed to filter into the test chamber under mild pressure. It is possible to detect immediately leaks in the mask and determine exactly where they occur, whether in the fabric, in the mechanism, or about the edges, by examining both mask and subject under ultraviolet light, a bright green luminescence showing entrance of luminescent powder into the mask. Or, liquids and vapors can be used instead of powder, depending upon the type of gas, smoke, or fog the mask is intended for. This technique has very interesting possibilities when it is realized that unweighahle amounts of chemical can readily be seen on the skin of the face of the wearer or inside the mask with ultraviolet light. Many fluorescent chemicals are known which can be detected in dilutions as great as one part in several hundred million. Moreover, the gas-tightness of boxes, food and medicine containers, suits, and other objects, can be tested by the improvisation. Arson and Ex~losions. Traces of chemicals, explosives, and corrosive substances in bombmgs, sabotage, and related acts of violence may be studied by the means of fluorochemistry. The wax paper wrappings from dynamite and other explosives, or hits of paper from fuses and detonators, frequently fluoresce brightly. Many waxes fluoresce, and with the aid of the fluorescence spectromicroscope very slight differences can be brought out. Some of the gums and glues used to put bombs together may show fluorescence. Of interest is the damage performed by dyes thrown on garments or perishable objects. Many dyes are fluorescent and this can help in tracing their source, and also for the rapid examination of suspects apprehended immediately after such an act. Brilliantly fluorescing substances can be incorporated with the wrappings of explosives or other dangerous substances in order to trace the course of their lives, and to determine when, where, and under what circurnstances they were employed. Many of the glyceryl derivatives show a bright fluorescenceunder ultraviolet light: however, dynamite or other explosives such as trinitrotoluene do not exhibit a strong or characteristic emission. Mannitol derivatives may show luminescence, as is often the case of other complex organic substances used in the make-up of explosives.
Luminescent Ma@. The use of fluorochemistry in cartography and documentary work is now an established and valuable fact. The paper upon which military maps are printed can be rendered fluorescent by one of several methods which have been developed. These luminescent maps and documents enable reading during a blackout and a t night, and prove especially important in night bombing and for use in the night operation of naval units. The fluorescent maps glow brightly enough so that the printing can be read without other visible light, but so that the light from the map cannot be seen by the enemy close a t hand. Hence, maps and other documents can be prepared so as to be studied and read under the adverse circumstances of warfare. A method has been developed in which an ordmary map can be read by fluorescence without altering the paper or injuring it in any way. Dr. H. C. Dake of Portland, Oregon, in collaboration with the writer, has developed a series of techniques by which maps can be rendered permanently or temporarily luminescent (16). For an ordinary untreated map a cover of fluorescent plastic, resembling cellophane, is used and illuminated with an argon bulb or other feeble source of ultraviolet. Or, a fluorescent powder such as anthracene or a phosphor, can be merely dusted over the surface of the map and excited with ultraviolet light. The luminescence evoked is sufficientfor reading. Maps which are of little value or are to be destroyed, as is often the case in warfare operations in enemy territory, can be treated with lubricating oil and read under ultraviolet light a t night, the bluish glow of the oil providing su%cient light for reading. The simple application of anthracene or other fluorescent powder is easily done. After dusting, it is rubbed over the surface of the paper with a cotton pad or with the clean palm of the hand. The surplus is blown off. This treatment does not alter the color of the paper, and stretching, wrinkling, or other objectionable physical changes are not produced. Notations and additional writing can be made in ink or pencil, and the pencil mark later erased if desired. The powder becomes lodged in the pores of the paper and does not change surface characteristics or color in so far as the eye iuspection in white light is concerned. For purposes of national defense and under emergency conditions where visible light may be extremely undesirable or impossible, fluorescent maps, charts, diagrams, field orders, and other matter offer the solution to reading in the dark. The military scientist working in the darkness of the laboratory, as is frequently a necessity in investigational work of any kind, may need to make notes or read notes, or a lecturer may find i t necessary to darken the lecture room in order to demonstrate an important point fully, while illustrating his points on the blackboard with fluorescent crayon or chalk. Ultraviolet light and fluorescence answer these and similar problems. Thus fluorochemistry makes it possible to read, as well as write, in the dark. Fluorograflhic Fingerpinling. For bringing out fin-
canti-Glo Photo
THEULTRAVIOLET HAND LAMPCANEASILY BE IN0
USED FOR
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FLUORESCENT MAPSAND DOCUMENTS 1N THE DARK
gerprints on multi-colored surfaces a method depending upon fluorescence in ultraviolet light is often useful. The method involves the photography of a brightly fluorescent chemical which is used instead of ordinary fingerprint powder: it is known as fluorographic fingerprinting. A fingerprint consists of the sweat and oily secretion of the skin and although it may be almost invisible in ordinary light, the mere dusting with finely powdered anthracene or a phosphor will suffice to render it visible under ultraviolet light. Another method of fluorographic fingerprinting is to dust the luminescent powder directly on the hand or palm, thus eliminating the need for inking and the recording of each linger impression individually. When the hand is properly dusted, and it requires some practice to accomplish this, one photograph will provide a record of all fingers as well as the palm. Such a photographic fingerprint record can then be enlarged to any desired size so that fine detail is brought out, and any number of copies may be made. Photographs can be cut and single prints pasted into the squares of the conventional fingerprint card. This kind of fingerprinting proves especially valuable for obtaining a record of a large number of people within a short time. It also completely eliminates any inking procedure and has the advantage of being operated without the knowledge of the subject. In several forms of criminal and military investigation it is often desir-
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CRIMINALS AND SABOTEURS ARE NOT CAUGHT "KED~HANDED" SURFACE IM~ERFECTIGNS ARE READILY REVEALED ON FINE ANY MORE,BUT "GREEN-HANDED" BECAUSE GREENFLUORESCMETALPARTS, SUCH AS METAL BEARINGSOR THE SMALL SPRISG ING S U ~ S T A N C E SARE USED I N MARKING A N D TAGGING OBJECTS SHOWN ABOVE, BY USE OF FLUORESCENT FLAW-DETECTTON METHODS
able to obtain a complete record of hand structure without the subject's knowing about it. Fluorographic fingerprinting is an example of the many uses of fluorography, the photography of fluorescent light. I t is the same in principle as other methods used for the detection of surface defects, blowholes in fine metal castings, and for the study of structure in paleontologic specimens. With fluorography it is possible to determine the size and configuration of microscopic-sized scars, skin defects, metal, plastic, and paper flaws, and the like. When used in conjunction with luminescence microscopy it proves of even greater value. Fluorescent solids and liquids are used for the inspection of high grade metal bearing surfaces which must be absolutely free from surface imperfections. A flaw in the surface of metal bearings going into the make-up of delicate electrical or aviation instruments may cause considerable damage at some later time. For magnetic metals small particles of iron or iron alloy are coated with a phosphor and dusted on the object arranged in a magnetic field. The luminescent particles stick about the edges of flaws, as well as fill them in, so that it is possible to reveal their presence photographically. For large castings oil-like fluorescent materials are introduced under pressure and after the object is wiped
clean and the pressure reduced each flaw begins to show its presence and shape by a brightly fluorescent spot. Distinguishing Real and Apparent Death. It has long been a problem in emergency medical work to determine quickly, simply, and reliably whether or not a person is really dead. It bas been on the battlefield where such difficulties are most often encountered, especially in the sorting of many bodies which have just been subject to shellfire and bombing, and where the result may be such as to simulate death very closely. The distinction between real and apparent death has a number of significant implications for fields outside that of warfare. In the laboratory it is especially desirable a t times to establish objectively the time of death in an experimental animal. In peacetime the problem has numerous variants: in determining the viability of an apparently stillborn child; for determining whether or not the use of artificial respiration, the pulmotor, or other means of resuscitation should be continued or ceased; asphyxiation, poisoning, shock, psychoses, convulsions, and many other conditions are known to induce a deathlike state. The significance of the "golden hours" in the life of a recent casualty need hardly be emphasized to those who have ever had to cope with any type of injury, most particularly that of extreme shock. Under the stress.
of battle fire, lack of trained personnel and other adverse conditions of actual warfare, even a trained medical man may not have sufficienttime to make a detailed inspection of all casualties. It is under such circumstances that an apparently dead body may easily be mistaken for an actually dead body, and proper treatment delayed or wholly neglected. Very few reliable tests for death have ever been developed, most of the earlier methods being on a par with the placing of a mirror before the mouth or nostrils, or placing a feather or other light object on the chest to indicate breathing. In cases of apparent death the stethoscope and other modern instruments may fail. Hence, objective tests for death assume an importance which cannot be overlooked. It is during wartime, however, that testing for death becomes most appreciated. There has been develo~eda fluorochemical test for death which shows a great deal of promise, having been subject to a number of tests on living and dead humans and animals to prove its efficacy. The procedure in this test is to inject uranin or sodium fluoresceinate solution intravenously and inspect the lips, eyes, and site of injection under short wave length ultraviolet light. The investigators who worked out the basic details of this test, Dr. H. C. Dake and the writer, have shown that when true death exists in a body no very apparent change occurs in the fluorescence of the eyes, lips, and site of injection. In the apparently dead, however, it has been demonstrated that a strong, but dull, green luminescence appears in the lips, and a slight luminescence is seen about the site of injection. Moreover, the natural lumiuesceut response of the eyes may show a change when death occurs (8,9). The remarkable luminescent properties of fluorescein and its sodium salt, uranin, have been known for many years. It has often been used to trace the course of underground rivers, and for the detection of contamination of water systems by sewage. Fluorescein may be detected by its fluorescence a t dilutions as great as 1:40,000,000 with the unaided eye, and by instrumental and chemical means i t may be noted a t concentrations of 1:200,000,000 (9). Thus, the uranin test for death is over a thousandfold times more sensitive than similar tests which have been dependent upon color changes in white light. Other Medical Uses of ~luoro/chemistry. Luminescence has provided a number of sharp weapons for use in military medicine. The "green lips" test which has recently received so much public attention is an outgrowth of fluorochemical knowledge. The test enables the military surgeon to tell whether or not a frozen, gangrenous, or injuredfoot or arm should be amputated, and it provides a number of other valuable approaches to the detection and identification of certain kinds of disease and trauma. The test is essentially a uranin one, since it depends upon the injection of uranin and observing the result under ultraviolet light. It derives its name from the green fluorescence seen on the lips, and was developed by Kurt and Lange (17) of New
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PHOTOGRAPHY IN C O M ~ T NULTRAVIOLET ED A N D VFIBLEL I G H ~ SHOWSSGRBACE DEFECTS,SUCH AS THOSEIN SKIN. WHICH BE S E ~ N WITH THE UNAIDED EYE CANNOT
York, although some time previously D. Fishback (18) employed a very similar technique for the accurate measurement of circulation time. Since then the principle has been broadened greatly and its value realized in many branches of medicine and surgery. By injecting uranin or fluorescein intravenously, and inspecting the lips under ultraviolet light, i t is possible to determine exactly how fast blood is flowing through the body. This means that in cases of gangrene or injured intestines, there will be an interruption in the flow of the dye through the blood vessels: thus, for limbs which are to be amputated it is possible to tell exactly where this should be done, as the green fluorescence disappears at the junctionof living and dead tissue. Determinations of circulation time are important for detecting the presence of heart disease, such as arteriosclerosis, and for detecting. func- anomalies. in plandular tioning. Other medical applications of fluorochemistry to military medicine include delicate means for the examination of tissue structure. such as in the case of skin cancer and minute lacer&ions. There is an exceedingly delicate fluorochemical method for detecting the presence of, and the size and shape of corneal lesions. Uranin solution dropped into the eye, and viewed under ultraviolet light makes possible the detection of embedded particles and lesions, and the use of ultraviolet light will enable the surgeon to tell by its fluorescence exactly where a cataract begins and ends. Dyes such as acriflavin, flavophosphin, eosin, and many others fluoresce brightly and may be employed instead of fluorescein or uranin. LITERATURE CITED
(1) STOKES, Phil.Trans., 143,463 (1852); 144,385 (1853). ( 2 ) DE MENT,Science, 95, 407 (1942); Mineralogist, 10, 234 (1Q42) ~.. .-
(3) DAKEAND DE MENT, "Fluorescent Light and I t s Applica(Continued on page 154)
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FLUOROCHEMISTRY IN MILITARY SCIENCE (Continued from page (4)
(5) (6) (7) (8) (9) (10)
tians," Chemical Publishing Company, Inc., Brooklyn, New York. 1941. DE MENT, "Fluoro~hemistty,'' ChemicalPublishing Company, Inc., Brooklyn, New York (in press). I n this hook will be found a complete treatment of the theoretical foundations of fluorochemistry. SE~nnooK,"Dr. Woad," S e w York, 1941, pp. 205-6. Cf. AUDUBERT, Trans. Faraday Soc., 35, 197 (1939). and reference (4). RADLEY,personal communication from Manchester, England, 1943. Cf. DE MENT,Militmy Eng., 34, 538 (1942). DAKE AND DE MENT, ''Ultraviolet light and its applications," Chemical Publishing Company, Inc., Brooklyn. New York, 1942. DEMENT,Refiner Natural Gasoline Mfr., 21, 81 (1942) and
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subsequent papers in this journal and in Oil Weekly. WOOD,I. phys., 9 (1919). See Science News Letter. 42, 126 (August22, 1942). A list of many fluorescent chemicals is to be found in DE MENT, "Fluorescent chemicals and their applications," Chemical Publishing Company, Inc., Brooklyn, Kew York, 1942. See Science N m s Letter, 41, 345 (1941); Mineralogist, 9, 338 (1941). See Science N m s Letter, 42, 265 (1942); Geol. Nevs Letter, 8,179 (1942). See BENNETT,"The (new) Chemical Formulary." Volume VI, Chemical Publishing Company, Inc., Brooklyn. New York, 1943. See Science News Letter, 42,325 (1942) for a good account. F ~ s x s n c J. ~ ,Lab. Clin. Med., 26, 1966 (1941).
