INDUSTRIAL A N D ENGINEERING CHEMISTRY
1138
As pointed out above, the disturbing factor in the accuracy of the final result with the ordinary bomb is the variable quantity of air which still remains in the apparatus. If it were possible to know how much of the recorded pressure
Vol. 17, No. 11
is due to this air, it would be easy to calculate the true tension of the gasoline. I n a sense, this is what the vapor tension device with a visible indicator tube, described above, is designed to accomplish.
Evolution of Hydrogen Peroxide by Oils on Exposure to Light’ By G. F. A. Stutz, H. A. Nelson, and F. C. Schmutz NEWJERSEY ZINC CO., PALMERTON, P A
USSEL,2 in a series of researches, demonstrated that a number of metals, seeds, roots, bulbs, and oils and resins from vegetable sources affect a photographic plate in a manner similar to light. On placing a sensitive photographic plate in contact with or near such materials, i t is so affected that upon development by the usual method a n image is produced. He produced strong evidence that this action is due to hydrogen peroxide evolved from the materials, which makes the sensitive plate developable. Otsuki3 and Saeland4 confirmed the findings of Russel. The characteristics of the action of hydrogen peroxide upon a photographic plate have been studied in detail by Sheppard and Wightman,s and found to be similar to that of light in every respect. (Other agents, such as ozone, are known to produce the same results.) Baughman and Jamieson,6 besides submitting further proof that the action is due to hydrogen peroxide evolved as a vapor, find the effect with oils to be greatly increased on exposure of the oils to sunlight. They also find that the saturated fatty acids of the oils are inactive and the unsaturated fatty acids, strongly active. Clearly, the phenomenon must be associated with the drying of a n oil. Further, it seems very probable that it should be associated with the entire process of the oxidation of an oil film, from the beginning to the final stage, when it becomes a brittle, nondistensible mass. The present investigation was undertaken because i t seemed possible that a study of this phenomenon would give further information about the mechanism of the action of light on drying oils. I n particular, it also affords ready means for determining whether light is selective in Its action on oils-that is, to what extent the effectiveness of light is dependent on wave length. This information is of special importance because of the present interest in accelerated weathering,’ where
R
1 Presented before the Section of Paint and Varnish Chemistry a t the 69th Meeting of the American Chemical Society, Baltimore, Md., April 6 t o 10. 1925. a Proc. Roy. Inst. Great Britain, 16, 140 (1899-1901); PYoc. Roy. SOC.London, 7 8 , 3 8 5 (1906), and 80, 376 (1908). 8 J. SOC. Chem. I n d . , 24, 575 (1905). 4 A n n . Physik., [ 4 ] 26, S99 (1908). J . Franklin Inst.. 195, 337 (1923). e J. Oil Fat Ind., 2, 25 (1925). 7 Nelson, Proc. A m . SOL.Tcsling Materials. 22, Pt. 2,485 (1922); Nelson and Schmutz, Ibid., 24, Pt. 2 , 920 (1924).
it is proposed to apply intensified light action (as well as other agencies) in deteriorating organic protective coatings. Obviously, in order to do this effectively, light from the most active regions of the spectrum should be employed. Any test that enables us to determine these active regions will thus be of considerable practical value. Method
The oil is placed in a suitable dish if wet, or on a glass plate if in the form of a dry film. A sensitive plate is placed over it, in a light-tight box, a t a distance of from 0.1 mm. to 2 cm. (usually 5 mm.). The evolution of hydrogen peroxide may be nearly complete within an hour, but the reaction with the film may require 18 hours or more for completion. Warming the plate will hasten this latter reaction. I n these experiments, the plate was placed in contact with the oil for 18 hours and then developed. Eastman 33 plates were used with a standard pyro developer; time of development was 1 minute. Sheppard and Wightmans found that for concentrations of hydrogen peroxide of tfle order of magnitude observed in these experiments the opacity of the image produced is a measure of the concentration. The opacity is the reciprocal of the transmission. The transmission was measured by a special microphotometer, designed by A. H. Pfund. The results given in this paper are in terms of opacity, and are therefore a proportionate measure of the hydrogen peroxide concentrations. The opacity produced by a standard sample of raw linseed oil, after exposure to the quartz mercury light for 5 minutes, has been taken as the basis for comparison. I n order to obtain reproducible results, where exposure to light was involved, the samples were exposed a t a distance - of 36 cm.-(14 inches) from a quartz mercury vapor lamp (horizon t a l Cooper-Hewitt burner) burning a t constant current and voltage. Characteristics of the Effect
Any source of light containing blue or ultra-violet light, as well as sunlight, will increase the effect. Such light is found to be instantaneous in its action and, with some oils, a maximum effect is attained after a few m i n u t e s ’ e x p o s u r e . The h y d r o g e n peroxide vapor given o f f under these circumstances did not discharge an
INDUSTRIAL AND ENGINEERING CHEMISTRY
November, 1925
T a b l e I-Sensitivity Acid number 6.8 0.5
Iodine OIL number 0 0.5 1.01 Raw linseed 186 3.0 Alkaline refined linseed 10 21 Alkaline refined refrigerated linseed 3.5 4 8 Acid refined linseed 313 11.0 370 Air-bodied linseed 133 36 144 9 22 D r y film air-bodied 73 Drv film (litho.) 16 10 Dr> film (raw oil) 64 9.0 Commercial tung 1.0 164.6 4.8 1.0 American tung 3 171.8 0.2 Poppy seed 139 8 . 9 15,500 20,800 129 2.3 8 20 Soy bean 124.6 7 . ,5 3600 Sunflower seed 3600 20,800 Lumbang 152 1 . 0 15,600 270 745 Chia 196.3 0 . 6 Castor 84.4 1.9 5 6 1.0 Olive 85.0 3.7 1.0
....
OPACITY AFTER
3 110
of Oils
EXPOSURE TO
16 I09
383
5 100 580
25 326 236 139 26
75 432 746 130 31 167
84 432 1110 137 27 200
19,000 209 5100 19,000 1530 22 5
17,500 248 6110 17,500 2780 32 12
1
100
....1.0 21,500 61 4530 21,500 795 12 4
....1.0
electroscope. Placing a quartz or glass plate between the oil and the sensitive plate eliminates the effect. A 0.01 per cent solution of hydrogen peroxide in water produces an image comparable to the effect produced by a linseed oil after exposure to the light for one hour. T o determine the duration of the effect after exposure to light, a fresh plate was placed in contact with an exposed linseed oil every hour, for 6 hours after exposure, and the plates were then allowed to stand 18 hours before development. Practically all of the peroxide was evolved in the first hour, but little in the second hour, and only a trace in the third hour. Since the temperature of a n oil, when exposed to the mercury vapor lamp, was raised to approximately 50' C., it was advisable to determine the effect of heat. Raising the temperature of linseed oil 30 degrees (from 20" to 50" C.) was observed to give an increase in opacity of one, after 2 hours. A rise of 55 degrees gave an increase of three. Prolonged heating a t these temperatures gave no further increase. This increase is generally less than one per cent of the increase caused by exposure to light for the same length of time. Sensitivity of Different Oils
To determine the effect of varying the time of exposure to light-that is, the sensitivity of the oil to light-samples of several drying, semidrying, and nondrying oils were exposed. The samples of each oil were placed under the light at successive intervals so that all were removed and put in contact with the same plate a t the same time. The resulting opacities appear in Table I. Figure 1 shows the characteristic sensitivity curves for a few representative oils. Some points of particular interest in these data are worthy of note. I n general, the drying oils reach a maximum and then decrease within 2 hours of exposure, while the nondrying oils show a steadier increase with no maximum, in the same period. The indication is that in the case of drying oils a rapid reaction, confined chiefly to the surface, takes place with the formation of a skin which is relatively impervious to hydrogen peroxide. If this skin is broken by stirring, hydrogen peroxide is again actively evolved. The difference between Chinese tung and American tung oils is striking. Solidified films show little production compared with the same oils in a liquid state. An air-bodied oil shows a more rapid and a greater increase than the untreated oils. Effect of Acidity of Linseed Oil
Baughman and Jamieson found the effect to be greatest for the free unsaturated fatty acids extracted from an oil. Accordingly, i t was supposed that the addition of mixed fatty acids to an oil would increase its effect. The results of a few tests, as recorded in Table 11, do not entirely confirm this assumption. I n the case of the refined oil there is a
1139
:.
MERCURY
10 190 315
0
LIGHT
(L?~IAY!TES)--
15 650 625
20 1240 873
30 2030 1015
40 1800 1530
1760 2000
10s 167 400 400 692 1440 42 31 27 37 145 99 1.01 2 32 46 16,900 20,600 1640 2780 2150 3040 16,900 20,600 10,200 14,000 24 43 3 6
127 400 1300 27 40 118 4
237 462 2840 23 40 150
306 462 2230 44 38 115 2 49s 25,000 12,200 3930 25,000 19,600 260 764
584 570 3680 59 800 120 7 2430 37,400 4590 7450 37,400 20,700 559 2920
11
21,300 6300 3820 21,300 17,700 100
25
1
64 23,200 3270 3380 23,300 16,900 161 291
60
120 1820 2130 851 462 2840 57 923 120 D
1370 20,800 5460 11,900 21,300 18,100 1270 5740
marked decrease within the range observed. At greater acidities the effect might again increase as i t has in the case of raw linseed oil. T a b l e 11-Oils
Doped w i t h Free F a t t y Acids Ooacitv - _ - - - ~after - -~ 5 minutes' exOpacity Acid posure to H g number light unexposed OIL Alkaline refined 0.5 330 8: Alkaline refined doped 52 3.0 Alkaline refined doped 29 5 4.6 Alkaline refined doped 15 3 8.0 Alkaline refined doped 5 9.9 11 Free fatty acids 81 178.0 22 Raw linseed 27 1.9 14 17 1 4.4 12 7.9 1 27 9.8 1 Acid refined 120 4.2 1 7.2 Acid refined doped 34 1 Acid refined doped 28 10 1 (I An opacity of 1 corresponds t o complete transmission-i. e., n o image was produced.
Effect of Humidity
Solidified films of three oils were brought to constant humidity conditions a t 0, 30, 60, and 80 per cent relative humidity. They were exposed to the mercury vapor lamp for 10 minutes, in quartz cells maintained a t the same relative humidities, then put up with sensitive plates in desiccators at these humidities for 18 hours. The resulting opacities are recorded in Table 111. The maximum effect for the films not exposed to light is a t 30 per cent humidity. On exposure to light the maximum effect is evident under desiccated conditions. Addition of Pigments
The results obtained on exposing a 50-50 mix (by weight) of pigments in oils are given in Table IV. Soaps
The effect produced by several metallic soaps, typical in their variations of drying properties when mixed with linseed oil, is recorded in Table V. Soaps that greatly accelerate drying show no effect, while those that accelerate drying but little show a strong effect. A sample of lead resinate containing 30 per cent free resin shows a n appreciable effect, but the pure soap does not. Spectral Distribution of the Effect
To determine the relative effectiveness of various regions of the spectrum, a series of filters transmitting different portions of the visible and ultra-violet ipectrum was employed. The total energy below 14,000 A. transmitted by each filter was determined by means of a thermopile and sensitive galvanometer. The time of exposure of the oil under each filter was adjusted to give the same total energy.
...... ..
.......
cap.eI?tTal distril)ution of the d e r 3 will be furt,her verified, iiritig the iroii :ire and sunlight. r . 1his pitpor is entircly of a greliiniiiary tiaturr, and tile work is bcirig contirrusd imtli to verify furtlirr tlie grniwil rwult. givcn imid to r&uge opm its s i y x
/ n h m e ~VSprcmID i W ~ b u h n '?"'e 0rLiposoir fii L,@f rm
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this apparently greater rvoiutioii :it clixiccated coriditirnis I'ail ]iOssih~yhe explnililY~a6 d U P +,it tlte hwer vapor JiressUrc in tlii' surrr,umling a t m o s p t i i w , which will enc,ouragc thr pe of these volatile products. hat thc evoliition of apprtwiable quantities (if hydroaim peroxide is rlapendeot 011 rxposiirc to light has been plaiiily showir. Further, the arclerating effect of light in causing tlir solidificiitirm of an oil film is well knowii. In this connect,ion it is uf interest to note t.Iiat Eibner" inaintiiinn that tit(! iiiitiul oxygen absorption is not dependent on light, but timt tlie transforrimtion of peroxidrs arid the siilisequerit formnt,ir,t, of volatile denimposition products are dependent on light. W i i l f f ' ? inaiiitairis that. in variiishes exposed t,o light containing short wave lengths, oxidation and polymerizatirm priwced at almost equal rates. On the other hand, in light of longer wave 1eogt.lis polymerization is retarded more t.liaii oxidation. If we assume that by po&mcrization hr m e m i the reactions that result in the evi~httiouof such vnlatilv i)rixluots as hydrogen pernxide, the evidence that wave lciigtlis i%Iiuvc4300 1.fail to st,imulate the evolution of hydrogori peroxide xould iudicabe bhat he is correct. (See FiRiirr- 2 :!ad a) In the, rase of tlic metallic soaps, the fact that the sonpi o I
the strong drying metals fail to evolve hydrogen peroxidc. ivhile the relat.ively tiondrying soap how it strongly, is o I particular interest. Either the hydrogen peroxide is riot formed at all,or it reacts with the met,id to fwm The latt.cr view is subfitantiated by the f experimemt:s, only the soaps of thofie t i forming higher oxides shov no hydrogen pe Coffey'a makes the statement t,liat in the (I'bO) no trace of hydrogen peroxide is found. In his experiments he dusted the dry oxides on the surface, and c ( m scquetitly the coticeritrat~ionof drier at t.he surface must h a w hecn relatively high. I'reliniinary experiments by the authors hare indicated t.liat thc presence of normal amounts of driers 9 Traube, " V o r ~ a w rder Aatoxydation," Vieweg, Brunswick. 1909; CoBey, J , Cham. Soi. (London),119, 116s;Zaglei, Be,., 33, ( 7 ) , 1090 (19OOi
'OC. .,I., 18, 2970 (1924). Porbm-Zlg., 16, 0397 (1921). J /
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