Radioactive Materials in Growth in Optiea
evention of
SIGMUND BERK AND LEOYARD TEITELL Pitman-Dunn Laboratories, Frankford Arsenal, Philadelphia, Pa.
T
tive in preventing the growth and sporulation of a number of species of fungi ( I , 2 ) . It was concluded that the alpha particles from the radioactive materials were responsible for the fungistatic effects obtained. Vicklund ($0) treated with radium foils the five lenses from the telescope of an engineer transit and exposed i t in a tropical chamber. Re found the treated instrument free from mold growth after 12 months' exposure. In this investigation an attempt mas made to protect a more complex optical instrument. containing prisms, with radioactive materials. In order t o protect the optical elements, certain binocular parts (Figure I) were covered with a gold foil containing radium, coated with a radioactive lacquer, or plated with polonium. The effectiveness of the three radioactive treatments in eliminating fungus fouling of the treated instruments after 5 months' exposure in a tropical chamber is described in this report.
HE deterioration of optical instruments in tropical areas has been recognized for some time, but the problem \Vas not given serious consideration until World War 11. With the advent of global war large numbers of binoculars, telescopes, range finders, cameras, and other optical instruments were shipped to areas where climatic conditions were favorable for the ingress of moisture and the growth oE fungi. The lenses and prisms in the equipment used or stored in such areas became overrun with fungus growth. The only practicable preventive measure used a t the time was storage under dry conditions. An extensive investigation of preventive and control measures was undertaken by the Office of Scientific Research and Development and government laboratories in America, Great Britain, Australia, and India. These investigations were revien-ed by Teitell and Berk (18).
Binoculars given a number of treatments and exposed a t a test site in the Panama Canal Zone showed that a volatile fungicide, m-cresyl acetate, offered the best protection (18). Two binocular telescopes treated with a radioactive metallic foil in the vicinity of each optical element also were protected against fungus attack, However, the prism surfaces of these telescopes which were not protected with the radioactive foil became ovprrun with fungus groxfth. The radioactive foil treatment will give years of protection to the instrument, whereas the use of a volatile fungicide requires periodic renewal of the chemical. Ionizing radiations from radium and polonium were found effec-
OPTICAL ELEMENTS REQUIRING FLZVGUS-PROOFING
Figure 1 is an exploded v i m of the left telescope of the h13 binocular (6 X 30), showing the optical elements that require fungus-proofing. Each half of the binocular is a terreitrial telescope with Porro prisms as the erecting system. In the A13 binocular the reticle is in the left telescope. The right telescope is similar to the left, except that the reticle and adapter are absent. RADIOACTIVE MATERIALS USED
O F h.13 BI~oculARSUNTREATlD TABLEI. RESULTSO F EXANINATIOX
TRE.4TED
AND
WITH RADIOACTIVE h'1ATERIALS
(During 5-month exposure in tropical chamber simulating average field conditions) First hopearance Extent of Mold Growthb and Fogging and of l l o l d Binocular Droplet Formation Growth, Treatment No." ~2 wk. 4 wk. 8 wk. 12 wk. 18 wk. 20 wk. Days
2. Radium lacquer
3. Polonium plated
Untreated
5R 6L 7L 8R 1R 2L 3R 4L 5L 6R 7R 8L 9L
R R 11L R 10L
Of 0
Of Of 0 0 0 0 0 0 0 0 Of 0
Of Of Ohf
Ohf
0 0
+ 0 0
Of Of
Of
+
0
0
0 0 0
0
0
0
Of +f Ohf
Ohf Of +f
+f
++ 0
+ +f + Of 3 Of +f
Of 0
Of
Of
+
+f ++
+f
Of Of
Of
Of
Of
+f
+f
+f
+f ++ +++ +++ ++++ ++++ +++ ++ ++f + f ++++ ++++ +f + +f
+f ++ +f ++ +4-3. +f ++ +++ Of +f +f
+ +f
Of
+ i Of +f
++ Of ++ ++ +f +
++++
98 54 e
ii9 61 40 19 61
54 33
98
70 29 126 42
35 112 77
Left barrel, has reticle. R . Right barrel. b Code for mold growth and appearance of optical glass. 0 N o mold growth. Trace to slight mold growth. Moderate mold growch. f . Fogging or film formation. Heavy mold growth. hi. Heavy fogging or film formation. C No growth visible after 5 months' incubation. Very heavy mold growth.
a
L.
+++++ + ++++
The introduction of radioactive materials plated on metallic foils as static eliminators for industrial processes (3, 6, % I ) offered a ready source of ionizing radiation for application to the optical instruments. The radium foil used was prepared by the U. S. Radium Corp. and is described elsewhere ( I ) . It consists of a mixture of radium and barium sulfates and gold powder with a silver backing for mechanical support. The thickness of the foil was about 0.003 inch and it contained l5y of radium per square inch. The alpha particle. from this foil have been reported by Evans (6) to have a maximum range of 6.9 em. of air. The foil contained a coating of nickel designed t o protect the surface from flaking and rorrosion. It has also been reported that the layer of gold and nickel prevents the esrape of radon gas (3, 6 ) . The radium-activated foil was cut into strips 1.5 and 2.0 mm. in v,idth and cemented to the metal parts with a neoprene rubber cement (Minnesota Mining & Mfg. c o . , Ec Yo. 870). The hatched areas or broken lines in the
April 1954
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
metallic parts (Figure 1) were treated with the radioactive materials. The binoculars were disassembled and reassembled with the radioactive materials by personnel of the Frankford Arsenal Optical Shop. For each binocular one telescope was treated and the other left untreated (Table I). Treatment 1 had approximately 287 of radium in the left 1. Eyelens telescope and 257 in the right tele2. Separator scope. The prism shields were only parE 3. Fieldlens tially protected (2.57 ,....._- 4. Ring retainer of radium) and t o c o v e r t h e m completely with the ra5. Reticle dium-activated foil would require 25.57 6. Adapter of radium. The total b concentration of ra7,13. Cork pad dium required would 8.12. Prism shield t h e n be approximately 747 for the left and 717 for the a right telescope. Binb 9. Upper prism oculars given treatC ment 2 were painted with a radioactive 10. Prism shelf lacquer obtained from the Radium Chemical Co., Inc., a New York, N. Y . b 11. Lower prism C The lacquer is a polyacrylic dispersion in water. The radium content was such that when brushed .,,..,..I 14. Objective ring on a glass surface, the c o n c e n t r a t i o n 15. Objectivelens was found to be approximately 157 per Figure 1. Exploded View of Left s q u a r e inch. InTelescope ofM3Binocular Showstrumentation was ing Optical Glass Elements not available a t the Hatched and broken linea show areas time to measure the of metallic parts proteated with radioacive materials. Right telescope duactual activity of plicates the left, exeept that parts 5 the treated surfaces. and 6 are absent Assuming a uniform distribution of the radium salt in the lacquer, and uniform thickness of the coating, the left telescope should have had 747 and the right 717 of radium. It was reported that alpha radiation is very effective in inhibiting the growth and sporulation of a number of fungi (1, $). Although the radium atom ejects alpha particles, i t also emits beta particles and strong gamma radiation. The beta and gamma radiation in sufficient dosage can be a serious health hazard to personnel. Gamma radiation easily penetrates the binocular body, whereas even a thin piece of metal foil will stop all the alpha particles. At the time the only available pure alphaparticle emitter was polonium, which has a short half life, 138 days. Polonium offers practically a monoenergetic source of alpha particles (5.3 m.e.v.) with a small amount of weak gamma radiation. The range of the alpha particles in air is 3.84 cm. a t standard conditions. If the alpha radiation from the polonium were found effective in preventing fungus growth on the optical elements in the instrument, other alpha-particle-emitting isotopes with longer half lives could be used. The following synthetic alpha-particle emitters with useful radiation energies and half
q: .......
E
-
,,flp-
mz
3
-
779
lives may become available: (1) 92U232(5.3 m.e.v.; half life, 70 years), (2) ,,Puea*(5.5 m.e.v.; half life, 90 years), and (3) ,;Am241 (5.5 m.e.v.; half life, 500 years). In treatment 3 the black-dyed oxide film on the metallic parts was removed prior to plating with polonium. The M3 binocular parts are made of aluminum die castings, except the prism shields, which are copper. The parts were plated with polonium by the Canadian Radium & Uranium Corp., New York, N. Y. The initial activity of the polonium-plated parts was 225 microcuries per square inch. Figure 2 is the decay curve for polonium and shows the activity of the plated optical parts a t the time of treatment, a t the time the binoculars were assembled, and a t the beginning and end of the exposure in the tropical chamber. The parts shown in Figure 1 were plated with a polonium band approximately 2 mm. wide, except that the surfaces of the prism shields which are in contact with the prisms mere completely coated with polonium. The approximate activity in the left telescope was 1120 pc. a t the time of plating and 428 pc. a t the time of exposure in the tropical chamber. The right telescope had 1010 pc. when plated and 386 pc. when exposed in the chamber. The polonium-plated surfaces were not protected against flaking. TROPICAL CHAMBER EXPOSURE
Prior to exposure in the tropical chamber, the untreated and treated binoculars were stored for 2 months in containers with silica gel, and then placed on a shelf in a tropical humidity chamber. The temperature and relative humidity conditions in the chamber approximated an average July day in the Panama Canal Zone. For 12 hours each day the temperature was maintained a t 76' F. (24' C.) and above 95% relative humidity. For the remainder of each day, the temperature gradually increased during 6 hours to 82" F. (28' C.) and then gradually decreased for 6 hours to 76" F. The relative humidity inversely followed the temperature changes, with a lowest relative humidity of about 78%.
8 ,...*.I '
-
50
100
150
200
250
300
350
DAYS
Figure 2. Decay Curve of Polonium on Treated Optical Parts A. B. C. D.
Polonium activity when parts treated Activity when parts assembled Activity a t start of tropical room exposure Activity a t end of tropical room exposure
Table I lists the extent of mold growth and degree of fogging or film formation on the optical glass after 2 to 20 weeks' exposure in the chamber. The condition of the objective lens and the Porro prisms was determined by sighting through the objective end of each telescope, and the condition of the eye lens, field lens, and reticle was ascertained by sighting through the eyepiece end. Figure 3 is an external view of the M3 binocular after 20 weeks'
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
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Vol. 46, No. 4
the radium lacquer had slight to very heavy mold growth, while the two polonium-treated telescopes were free from mold growth, except for a trace in one telescope. Figure 4 shows a view of some of the binoculars obtained by sighting through the objective ends of the telescopes a t the end of 5 months’ exposure in the tropical chamber. Droplet formation is shonn in radium foil-treated telescopes (3L and 4R). Telescope 6L treated with the radioactive lacquer had extensive mold growth. I n the polonium-treated telescope (7L) the optical surfaces appeared completely covered with small droplets. Extensive mycelial growth was found in the untreated telescopes (Figure 4, 3R, 4L, 6R, and 7R). Table I also lists the extent of filming and fogging of the binoculars during the course of exposure in the chamber. Fogging is considered a transitory condition of moisture condensation on the lenses (18). Filming is a more permanent thin layer of discontinuous droplet formation. After a few days’ exposure, Figure 3. External View of A13 Binocular after 20 Weeks’ Exposure in Tropical Chamber Note mold growth on vinylite cover
exposure in the tropical chamber. There is a $light growth of mold on the vinylite cover. After 12 days’ exposure in the room, no mold gromFth mas visible on the internal optical glass elements of the binoculars, but, the external viaylite covering of the binoculars did show some mold growth. All the telescopes had some moisture formation on the interior optical surfaces, but the polonium-treated binoculars had more droplet formation than the rest of the binoculars. Table I lists the number of days of exposure in the chamber when mold growth was first visible on the optical glass by sighting through the objective and eye lenses. The first signs of mold growth appeared on the prism of one untreated telescope (3R) after 19 days’ exposure. Hutchinson (8) found that untreated binoculars became moldy after 3 weeks’ exposure in Panama. After 9 weeks’ incubation, in most cases where heavy mold growth was present on the optical glass, there was no fog in the telescope. Similar observations were made on binoculars exposed in the Panama Canal Zone. It may be that the fungus growth is absorbing the available moisture from the instruments. After 5 months’ exposure in the chamber, the external examination by sighting showed that all the untreated telescopes had mold growth, two out of four telescopes treated with the radium foil had slight mold growth, t v o out of two treated with
4R
4L
6L 6R
b Figure 4. View of Binoculars Obtained by Sighting through Objective Ends of Telescopes after 5 Months’ Exposure in Tropical Chamber L. Left telescope R. Right telescope 3L and 4R were treated with t h e radioactive gold foil, 6L was treated with radium lacquer 7L was treated with polonium, and 3R, 4k, 6R, B’nd 7R were untreated
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.
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
April 1954 >a
0)
+ +++ + + E$ ooco ++ E2 3s-
fogging was visible on sighting through the telescopea. Droplet formation on the optical glass was visible on the polonium-treated telescope (8R) after 5 days' incubation. After 26 days droplets formed on the objective lens of the radium-treated telescope (2R) and on the reticle of the polonium-treated telescope (7L). Droplet formation was more prevalent on the binoculars treated with the gold foil and polonium than those treated with the lacquer.
+
++t+ c++++++++o++++
++
I I V 3
0000
o+
+ + ++++
781
i
88 o+++++oo+o++-z
LIGHT TRANSMIlTANCE AND KINETIC DEFINITION CHART EFFICIENCY
I - ++++ u ++u
9 ++ -+ T+
++++++ ++ ++++++ ++++++
5
g+ +++-++++++++ti E3
* + +++-+++ A+;+ ;e+ +++. ++++ ++ 80
+
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c
,273
+++t++
++++t+++++++++ $8 0
$6
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2
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+++ 88
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t+ + + ++ ++ ++ ++ ++ ++ ++ + +
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+++B
++ + ++ ++ + ++ ++ ++ t+ ++ + +
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21 s!
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FUNGUS GROWTH ON INDIVIDUAL LENS COMPONENTS
u
I ++ ++ r: + t+ ++++ J ,too ++ 02 c++++++++o+++i
ii
Light-transmittance studies using standard photometric procedures were made on the binoculars before and after 5 months' exposure in the tropical chamber. In addition, determinations of kinetic definition chart (K.D.C.) efficiency of the binoculars were made on an apparatus similar to the one described in U. S. Army specification (19). The method consists primarily in comparing the resolving power of a perfect telescope with that of the telescope of the binoculars under test, A few of the telescopes had slight losses in percentage transmittance and a large number had appreciable losses in kinetic definition chart efficiency a t the end of the exposure period in the tropirrtl chamber. There was no correlation betaeen losses in light transmittance and kinetic definition chart efficiency or between the various radioartive treatments and the extent of fungus growth on the optical elements, Jones (9) reported that the high humidity found in some regions is detrimental to lenses. More recently, Stockdale and Tooley ( 1 7 ) showed that there was a progressive attack on polished glass caused by high humidity, but that for some glasses the transmittance losses did not correlate with the amount of visible attack. The latter results are in agreement with the light-transmittance results obtained in this study.
A+
+ + + + + ++ gtoo o+ 0 0 ++o+++o+++++o+
O Q
At the end of the 5-month tropical-chamber exposure, the binoculars were disassembled and the individual optical glass elements examined for extent of fungus growth and filming. Table I1 lists the observations made. Some of the lenses and prisms had mold growth a t the edges which could not be seen by sighting through and teIescope. I t was found (Table 11) that the decreasing order of susceptibility to fungus growth of the optical elements in the untreated telescopes was as follows: reticle, hypotenuse surface of upper and lower prisms, field lens, eye lens, objective lens, and rightangle surfaces of the prisms. Figure 5 shows the type of fungus growth found on the reticle, field lens, and prism of untreated binoculars. Of the telescopes treated with the radioactive foil (treatment I), the eye lens and objective lens were conipletely protected, the field lenses and reticles had only traces of growth a t the edges in some cases, and the prisms were only partially protected. However, the mold growth on the prisms was confined to the edges or areas not protected by the radioactive gold foil. I n both the treated and untreated instruments, in many cases mold growth started not on the optical glass but on the metallic rings used to keep the optical elements in place in the telescope. I n the rings protected with the radioactive materials, mold growth started in back of the radioactive surface and grew onto the edge of the optical glass until inhibited by the alpha radiation (Figure 6,D). This fact may be one of the limiting factors in the use of radioactive materials to prevent mold growth in optical instruments. The radioactive lacquer offered little protection to any of the optical elements. It appears either that the lacquer shielded the radium to such an extent that the alpha particles did not escape from the lacquer film or that the radium settled out prior to application to the optical parts. The polonium-treated binocular parts gave complete protection
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
782
to all the optical elements, with the exception of a trace of mold growth on one of the prism surfaces. This trace of growth may have started from fungi germinating on dust particles which had contaminated the prism surface, Since alpha particles from polonium have a range of 38.8 mm. in air and 38.9 microns in fungus tissue, the presence of contaminants on a glass surface could readily shield the fungus spore from the radiation. If the
A
B
Vol. 46, No. 4
EFFECT OF RADIOACTIVE MATERIALS ON OPTICAL GLASS
Table I1 lists the presence or absence of droplets on the various disassembled optical glass elements. The droplet formation was confined primarily to the optical elements of the telescopes treated with the radioactive materials. Figure 8 shows the appearance of the large droplets on the field lens and prism of a polonium-treated telescope. The most pronounced formation of droplets was observed on the optical glass elements t,hat were protected with polonium. It must be considered that the activity in microcuries of the polonium-treated binocuhs as eight times as great as that of the radium-treated binoculars. These droplets appeared spherical when examined by sighting through the telescope (Figure 4, YL), but, upon disassembly all the droplets did not appear spherical (Figure 8,C). Many of the droplets had become smaller and had dried out into crystallinelike deposits. Xordblom (13) found that condensate droplets on the field lens, reticle. and eye lens of a 6 X 30 binocular wsre either hydrocarbon oils from the grease used or a combination of oil and a plasticizer from the synt'hetic rubber gasket. Stenstrom and Vigness (16)reported that oil drops on a water surface increase in diameter when they are irradiated with beta particles, and t,hat the diameter of the drops depends on the amount of radiation. I n t'his stud>-it was found that the size and number of droplets formed was far greater in the telescopes treatpd with thr strong polonium sources than thoee treated 1vit)hthe low-activity radium foils. Intense sources of alpha particles are known t o produce coloration in glass ( 7 ) . Monk ( 1 2 ) found that boron-containing glasses darken xvhen exposed to radiation in the nuclear reactors.
C
Figure 5 . Mold Growth on Optical Elenients of Untreated Binoculars Exposed i n Tropical Chamber A.
B. C.
A
B
Prism (1OL) Reticle (ZL) Field lens (2L)
fungus spore that was shielded germinatca, it will put out hyphal tips d i i c h will develop abnormally in the presence of the ionizing rlrdiat,ion until all growth ceases. The short range of alpha radiation in matter is one of its disadvantage? as a fungistat for optical instruments. The most difficult optical element. to fungus-proof were the primis. The rings of radioactive foil wmented to the prism shelf (Figure 1) or polonium plated around the circumferences of thr circles of the shelves did not protect the entire hypotenuse surface of the prism. I n almost all raws where polonium or radioactive foil was used, the only mold pov-th present' was in back of t,he protected circles. I n ordcr to protect the prisms completely, it is necessary to coat Kith the radioactive materials the recessed area of the prism shelf on which the Porro prism rests (Figure 7 , lower). FUNGUS GROWTH ON OPTICAL PARTS OTHER THAN GLASS
The disassembly of the binoculars exposed in the tropical chamber for 5 months revealed that fungi gron- even on the internal metallic surfaces. One binocular had extensive mold growth on the internal surfaces of the t w o telescope bodies. Kine out of the 22 telescopes had mold grov-th on the cork pads (Figurc i ,upper). The sealing compoundusedin sixeyepiececover plates (Figure 6 , A ) and five objective cover plates had ext,ensive mold growth. Figure 6,B, s h o w mold growth on the grease used in the eyepiece assembly of the binoculars. There was also mold growth on the reticle rings (Figure 6,c): the retaining rings (Figure 6,D), eye-lens cell, reticle cell, eye-lens separator, and prism shelves of some of the binoculars. Figure 6,D, shows extensive mold growth on an objective retaining ring in back of the inactive surface of the radioactive gold foil.
D
C
Figure 6. Fungus Growth o n Disassembled Optical Parts Other than Glass after 5 Months' Exposure in Tropical Chamber A. B. C. D.
Sealing compound of eyepiece cover plate (5L) Grease of evepiece assembly (1R) Reticle ring (8L). Arrow points t o section of ring enlarged. Objective retaining ring (3L). Arrow points to radioactive gold foil
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
April 1954
However, Monk (12) also found that by the addition of cerium oxides to the glass formulas, he could produce glass that did not color even after an esposure of 106 roentgens from an SO-curie cobalt-60 source. Kernohan and McCammon (10) reported that ionizing radiation produces color centers in optical materials. The continuous bombardment of alpha particles from radon stored in borosilicate glass tubes produces cracks in the glass container. However, the sources wed in this stud!. did not have sufficient activity to produce any visible coloration or cracking in the optical glaw
783
rials for the prevention of fungus fouling of optical glass offers a potential health hazard. Necessary precautions must be taken to prevent dangerous exposure to radiation. According to Evans (6), the eyes are more resistant to the effects of radiation than are other tissues. B
A
CORROSION
The prism shields in the untreated telescopes were subject to corrosion due to the exposure in the chamber. White corrosion products were present on the prism shields and in some specimens the bare copper metal was exposed. Figure 7 , upper, is an enlarged view of heavy corrosion on a prism shield clip. All the metallic optical parts t)hat were plated with polonium mere heavily corroded. The polonium-plated parts that sho\ved the most severe corrosion were: eye-lens separator, reticle cell, prism shield, prism shelf, and objectjive retaining ring. Figure 7 , lower: shows the corrosion of a prism shelf that had t'he three circular areas plated with polonium. Smyth (16) states that corrosion by water and aqueous solution was of great concern i n the atomic energy program. Water undergoes dissociation as a result of ionizing radiation. Slat,er (14) believes that the dissociation products of M-ater due to ionizing radiation can accelerate corrosion. N o information on the effect of ionizing radiation on corrosion ie available in the unclassified literature. C
HEALTH H'AZARDS
The maximum permissible exposure to various types of radiations, according to the Atomic Energy Commission, are: gamma, 300 mr. per week; beta particles, 300 mrep. per week; and alpha particles 15 mrep. per week. The use of radioactive mate-
Figure 8.
D
Droplet Formation o n PoloniumTreated Optical Parts
A . Prism (7L) B. Field lens (8R) C. Enlarged view of reticle (7L)(220X) D. Enlarged view of droplets or crystals on objective lens (125X)
There is some controversy on the contamination hazards resulting from the release of polonium from linear sources plated with polonium. Bryan and Silverman ( 4 ) reported that the constant bombardment of the alpha particles in the linear source releases into the surrounding atmosphere tiny particles of the gold contaminated with polonium. Evans (6) found no physicdl evidence that alpha-particle bombardment of the poloniumcoated linear foils can produce free flakes of gold contaminated with polonium which would constitute an inhalation hazard. It is known that polonium has an inherent migratory characteristic and i t is therefore advisable to cover the polonium plating ~ i t ah thin coating of nickel, gold, 01 tantalum. Vicklund ($0) cites comments of the U. S. Army Surgeon General on an engineer transit treated with radium foil. I t vas concluded that no more than 2 y of radium should be used adjacent to the eyepiece, not more than 1Oy within 1 inch of the eyepiece, not more than 20y total within 4 inches, and not more than 507 total in an instrument. The servicing of optical instruments treated with radioactive materials would present many health problems. Personnel would have to be instructed in the radioactive hazards involved, in the use of gloves in the disassembly and cleaning of the instiuments, and in the constant monitoring of the work area. The gamma radiation emittrd in a storage area containing a large number of binoculars trrated TI ith radioactive foil would offer a serious health hazard Figure 7.
Corrosion of Binocular Parts
Upper. Heavy corrosion of prism shield clip of untreated telescope. Note mold growth from cork pad underneath clip Lower. Circumference of circles in prism shelf, plated with polonium
(W
DI SCWSSION
The results of this study showed that ionizing radiations from radium and polonium in the concentrations used prevent mold
INDUSTRIAL AND ENGINEERING CHEMISTRY
784
growth on optical glass in binoculars. HoLvever, mold growth occurred on all surfaces which were not adequately protected, and on nonglass surfaces, such as metallic parts (retaining and reticle rings), cork pads, grease, and sealing compounds. The growth of fungi from nonglass surfaces to the margins of optical g!ms elements protected with radioactive materials offers a serious draqback to their use. Because alpha radiation is stopped by 39 microns of fungus tissue, it is conceivable that sufficient growth could occur a t the edges of the glass to stop the radiation. Radioactive emanations would not prevent the entrance of animal vectors, such as mites. The mites would die on the glass surfaces and could serve as centers of mold growth. The dead organism would shield any germinating fungus spores from the alpha radiation. Owing to the difficulty in protecting binoculars with radioactive materials and the potential health hazards in their application to the instruments, other methods for the prevention of the deterioration of these instruments should be considered. However, for the protection of simple optical instruments not containing prisms or for special instruments which cannot be pxotected by other means, the use of radioactive materials may be desirable. The internal surfaces of binoculars may also be sterilized periodically by ionizing radiation from high-voltage machines. I n order to use this external source of radiation, the optical gldsses now used will have to be replaced with glasses that do not darken when exposed to the high-energy radiation. ACKNOWLEDGMENT
Appreciation is expressed to C. C. Fawcett and E. R. Rechd of the Pitman-Dunn Laboratories and to the Ordnance Corps, Department of the Army, for permission to publish this paper. Special thanks are due IT. L. Steinbach for light-transmittance measurements.
Vol. 46, No. 4
LITERATURE CITED Berk, S.,J l y c o l o g i a , 44, 587-95 (1952). Ibid., 45, 458-506 (1953). Berman, I. L., and Earnest, E. P., Ind. M e d . and Surg., 19, 22930 (1950). Bryan, F. A , , a n d Silverman, L. R., “Interna: Radiation €1~7,t r y from the Use of Polonium in Static EliminaU. S. Atomic Energy Commission, AECU-343 (1949). Evans, R . D., “Extract from Report on Polonium Static Eliniinator Devices to Canadian Radium 6: Uranium Corp.,” 1949. Evans, R . D., J . Ind. Hyg. Toricol,, 28, 243-56 (1946). Friedlander, G., a n d Kennedy, ,J. W., “Introduction to Radiochemistry,” Yew Yolk, John Wilcy 6: Sons, 1949. Hutchinson, W. G., J . Bacterid., 54, 45-6 (1947). Jones, F. L., C h e m Eng. News, 19, 390 (1941). Rernohan, R. H., a n d l I c C a m m o n , G . hl., “Fading Characteristics of Gamma-Induced Coloration in High Density Glass,” U. S . Atomic Energy Cornmission. ORNL 975 (1951). l I o n k , G. S., ”Coloration of Optical .\laterials by High Energy Radiations,” U. S. Atomic Energy Commission, ANI, 4536 (1950). Monk, G. S.,Nucleonics, 10, S o . 11, 52-5 (1952). Kordblom, G. F., “Condensate Formation on the Interior Optical Surfaces of 6 X 30 Binoculars,” Frankfcrd Arsenal Ord, Laboratory, Memorandwn Rept. MR-379 (1947). Slater, J. C., J . A p p l . P h y s . , 22, 237-56 (1951). S m y t h , €1. D., “Atomic Energy for Military Purposes,” Princet o n , S . J. Princeton University Press, 1946. Stenstrom, W,, and Vigness, I., J . Chem. Phus., 5 , 298-301 (1937). Stockdale, G. F., and Tooley, F. V., J . Am. Cemm. Sac., 33, 11-16 (1950). Teitell, L., and Berk, S., ISD.EXG.CHEX, 44, 1088-95 (1952). U. 9. Army Specification 51-70-2C, “Optical Components for Fire Control Instruments: General Specification Covering the AIanufacture, Assembly and Inspection of,” 1951. Vicklund, R . E., I s n . ENQ.Cmar., 38, 774-9 (1946). TVillianiu. C‘. R.. J . I n d . Hag. Tozicol.. 30, 594-9 (1945). RXCEIV~X for review October 1 5 , 1Qj3,
. ~ C C E P T C DDecember
1 , 1933.
Thermal Isomerization of Gum Rosin J. S. STINSOX AND RAY V. LIWRENCE Naval S t o r e s Research Division, Southern Regional Research Laboratory, Olustee, Fla.
T
HE effect of temperature on the physical and chemical
properties of gum rosin is an important problem. Since the industrial utilization of rosin generally requires that it be processed at temperatures between 225” and 290” C., a study was made of the effects of temperatures in this range for time intervals up to 8 hours. As rosin is sometimes stored by resin manufacturers for a few days at temperatures around 155’ C., one run was included a t this temperature. It has been shown by others (2, 3, 8, 13, 14) that approximately one half of the acidic portion of rosin may be converted to abietic acid by thermal or acid isomerization. It has also been shown (3-7, 9, 12, IS) that on continued heating abietic acid undergoes several reactions, including dphydrogenation, disproportiondtion, isomerization, polymerization, decarboxylation, and anhydride formation. The acids present in rosin that cannot bc isomerized to abietic acid, such as dextropimaric, isodextropirnaric and dihydro- and dehydroabietic acids are fairly stable at temperatures of 250” C. Some decarboxylation of these acids may ocrur a t higher temperature, but this group of acids would be expected to account for a very minor part of the changes taking place in the rosin. Many of these changes are interrelated. For example, the increase in the Boftening point, the change in optical rotation from positive to negative, and the increased tendency for the
rosin to crystallize that occur with moderate heating are causrd principally by the increase in abietic acid content of the rosin. As this heating is continued or as the temperature is increased all of these changes are reversed. The optical rotation becomes more positive. there is less tendency to crystallize, and there is n gradual decrrdse in softening point. EXPERIMENTAL PROCEDURE
Guin rosin samples of 300 grams each were heated in threenecked, 500-ml. round-bottomed flasks equipped with stirrer. side-arm trap, thermometer holder, and nitrogen inlet tube The temperature was controlled within i.5’ C. and the sample4 were heated a t such a rate that approximately 20 minutes wa.i required to obtain the desired temperature. A slow current oi nitrogen (20 to 25 ml. per minute) was passed over the rosin to provide an inert atmosphere. Samples of each run were removed a t suitable intervals and grade, acid number, softening point, and optical rotation were determined. Saponification numbers were determined on the original and final products. Grade samples were allowcd t o cool in containers in the presence of carbon dioxide. Grade, acid number, saponification number, and softening point (ring and ball) were determined by ASTlI methods. Optical rotatior
