January, 1931
INDUSTRIAL AND ENGINEERIXG CHEMISTRY
fact that, over the pH range used, each system has a characteristic curve peculiarly its own. Effect of Fat Liquor on Volume of System Figure 7 shows the contraction in net volume of the system when chromed skin is fat-liquored. During the first hour there is a very rapid decrease in net volume, attaining a practical equilibrium at the end of l l / z hours. This rapid contraction would indicate a selective adsorption of the oil by the leather and would tend to strengthen the theory as advanced by Wilson that there is a chemical combination between the leather and oil.
53
Effect of Composition of Fat Liquor
Figures 8, 9, and 10 show the effect of the composition of fat liquor on the curves. Figures 8 and 9 show how the curve characteristics change when sulfonated neat's-foot oil is compounded with various amounts of moellon. Figure 9 shows the detailed changes in characteristics. These curves indicate that the moellon has the predominating influence. Figure 10 shows the influence of sulfonated cod oil upon the characteristic curve of sulfonated neat's-foot oil. The resulting curve for a 50 per cent mixture of the two oils in no way resembles the curves for either of the unadulterated oils.
Studies in the Drying Oils XIV-Rate of Oxidation of Linseed Oil at 160" C.' J. S. Long and H. D. Chataway2 LEHIGEUNIVERSITY, BETHLEHEM, P.A.
The rate of oxidation of drying oils at 160" C. deXIDATION plays a for the gas through the pump. creases as an almost straight-line function of the degree vital role in a t least Jvithin the central tube is the first stage of setof oxidation until gelation takes place. a glass plunger filled with Gelation ensues when a certain size or degree of soft-iron wires, and fitting tjng of drying oils and in paints, varnishes, and other complexity or of polarity of the molecule has been closely outside the central reached. It is only indirectly a function of the degree tube are two electromagnetic p r o t e c t i v e coatings. The oxidation of drying oils, both of oxidation. coils. Current is passed alterin bulk and in thin films has In the case of glycerol esters of unsaturated fatty nately through these, whereacids gelation or setting occurs when one ethylene upon t h e plunger within therefore been studied by many investigators (1 to 7 , linkage on each molecule of acid in the ester has taken moves rapidly back and forth, up sufficient oxygen to form a peroxide group. thus operating the valves at 9). In a previous paper by Chataway (1) earlier work The loss of carbon and hydrogen from drying oils either end and causing an along the same line is deby oxidation at the elevated temperature of 160" C. almost continuous circulascribed. amounts to only 2 to 3 per cent up to the point of t i o n of gas t h r o u g h The present paper deals setting or gelation. the a p p a r a t u s . The rate with oxidation of linseed oil of c i r c u l a t i o n m a y be and related substances by blowing oxygen through the oil in varied over a wide r a n g e b y varying t h e current bulk. A temperature of 160" C. was chosen, first because passing t h r o u g h t h e coils. Some difficulty was at this temperature the oil can be oxidized to the gel point encountered in the construction of the valves and finally within a working day; second, because it is low enough to the design of these was slightly altered (Figure 2). In minimize effects due to heat bodying alone. Thus linseed making such a valve the grinding in is done before the outer oil can be heated at 160" C. in an inert atmosphere for many tube is sealed on. The valve is then completed with little days without gelling. Incidently it is approximately half difficulty, way between room temperature and 293" C. (560" F.). The oil to be studied is placed in the bubbler, A , a Pyrex glass container 38 mm. in diameter fitted with a groundApparatus glass cap holding the inlet and outlet tubes, t ~ tz, , and ts. A diagram of the apparatus is shown in Figure 1. It The outer wall of the container which projects above the will be seen that the whole forms a complete circuit open can is necessary to afford a means of supporting the conto the air at no point. It is filled with oxygen which is con- tainer and also to hold the mercury required to make the tinuously circulated by means of the circulating pump, joint air-tight, The gas circuit may be "shorted" across E. The original pump was one described by Chatterji the outlet and inlet tubes by means of the three-way stopand Finch (Z),but the rate of circulation maintained by this cock, a. This is an essential feature to prevent frothing pump proved to be extremely irregular over short periods. For of the oil over the sides of the container while filling the this reason and also in order to avoid the possibility of apparatus with oxygen. Such frothing would lead to surcatalyzing the reaction by mercury vapor from the valves,' face drying as well as bulk oxidation of the sample and the pump was replaced by an all-glass electromagnetic one this would impair the value of the results. The outlet designed by Funnel and Hoover (7). This pump consists tube, tz, leads to sulfuric acid and soda lime (ascarite was of a central tube terminating a t each end in an upper and finally used and found to be satisfactory) a t B1 and BP, lower valve, each pair of valves constituting a passageway respectively. About 4 inches (10 cm.) of platinum wire are sealed into the apparatus a t Bz. This is maintained a t 8 1 Received September 19, 1930. Presented under the subtitle before red heat, just as in Orsat combustion pipet, in order to burn the Division of Paint and Varnish Chemistry at the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 to 12, 1930. the considerable quantities of organic compounds which * Archer-Daniels-Midland and William 0.Goodrich Fellow a t Lehigh are found to be untouched by the sulfuric acid. The water University. and carbon dioxide SO formed are absorbed by the soda lime a The danger of this was pointed out in a private communication by J. (or ascarite) in BB. L. Buchan of the Goverrnent Laboratories London, England.
0
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
54
Passing along the circuit, C and D are used in taking the volume measurements. C, containing sulfuric acid, serves as a delicate manometer to indicate the exact instant at which the pressures inside and out become equal. The time is noted and immediately the buret reading of the level a t which the mercury stands in D is taken. This is done when the mercury stands a t the bottom of D. As the reaction proceeds, oxygen is absorbed by the oil and the pressure in the apparatus decreases. Mercury is then added in the outer arm of D until the pressures inside and out again
E
Ti9 2
become equal. When the level on the inside arm is close to the top of the scale, the time and volume readings are again taken, The difference in the volume readings gives the amount of oxygen absorbed during the interval, and this divided by the length of the interval gives the rate of consumption of oxygen by the reaction. The volume of D is only 50 cc., and it must therefore be frequently refilled. This is done by turning the stopcock d, which is connected to a supply of pure oxygen roughly a t atmospheric pressure, and drawing off the mercury from D through the stopcock at the bottom. This does not take long and the amount of oxygen absorbed during the interval may be estimated and allowance made for it. If it is desired to follow the rate of the reaction more closely, one or more readings during the course of the adsorption of each 50 cc. of oxygen may be taken, or the reaction may be followed from minute to minute by marking every 60 seconds, on a sheet of paper placed behind C, the height a t which the sulfuric acid stands in C. After passing the measuring pipets the gas enters the pump, E, and from there passes through the flowmeter, F , finally returning to bubble through the oil in A , in that way completing its circuit. The volume of the apparatus is 590 cc. The oil to be oxidized is maintained -at a constant temperature within 1 0 c. by of an electrically heated oil bath, the resistante in series with the heater being SO adjusted that the bath temperature remains constant over long periods. The bath is suspended by means of a pulley and counterweight, and can thus be rapidly raised into position and rapidly lowered.
Vol. 23, No. 1
ated separately from the bubbler, which is merely swept out with oxygen through a’. When all is ready the stopcock a1is opened, the three-way stopcock, a, is turned so as to “short” the circuit and a t the same time to shut off the inlet tube tl (in order that the oil may not be forced back up this tube by any chance increase in pressure), and the two parts of the apparatus are brought together and the groundglass joints sealed with de Khotinsky cement. A brisk stream of oxygen is introduced through d, passing in both directions through the apparatus to a, thence to sweep out the bubbler, entering this by tz and passing out through ta (thus it does not pass through the oil and frothing is avoided). Finally, the circulating pump is started, and when there is no longer any possibility of air pockets remaining d and al are closed and the experiment is ready to begin. The oil bath is raised into position and 3 minutes are allowed for the oil in the bubbler to become hot, whereupon stopcock a is turned in such a way that the stream of oxygen thenceforth makes its complete circuit through the oil. The rate of circulation is immediately adjusted to a certain definite rate, 30 cc. per minute; i. e., the difference in level between the two arms of the flow meter F is maintained constant throughout an experiment and from experiment to experiment. The first volume reading may be taken anywhere from 5 to 10 minutes after raising the oil bath into position. The reaction proceeds for several hours until finally, after consuming approximately 12 per cent of oxygen by weight, the oil gels. The gelling point is taken to be that at which the circulating gas ceases to form bubbles while passing through the sample. This point is determined by observation, the oil bath being lowered momentarily as frequently as is necessary. After gelation oxygen continues to be absorbed, although at a rapidly decreasing rate (experiment 3) probably because the oil is no longer stirred, with the result that no fresh surfaces are being exposed to the action of the oxygen. The experiment is therefore considered to end at this point. A sample of the gas remaining in the apparatus a t the end of an experiment may be analyzed to determine its purity. At first, when sulfuric acid and soda lime alone were placed in the circuit, it was found that a considerable volume of some hydrocarbon gas collected in the apparatus during the course of an experiment. The gas i c the apparatus a t the end of experiments contained 20 per cent hydrocarbons, probably propane and butane. An unsuccessful attempt was made to remove this by adsorption on freshly activated silica gel. However, by the use of a glowing platinum wire the amount of hydrocarbon present in the gas stream returning to the oil is reduced to a small fraction of 1 per cent. Materials
Oil 1 is a raw linseed oil, iodine number 185, acid value 2.3. oil 2 is a break-free linseed Oil, iodine number 187, acid value 2.4. The esters were synthesized from Pure oleic and linolenic acids by the method previously described (8).
Experimental Procedure
Experimental Results
Since it is important to avoid frothing of the oil over the walls of the bubbler, the main part of the apparatus is evacu-
Each experiment gave data for a graph showing the rate of oxygen consumption. Representative curves are shown
January, 1931
I N D U S T R I A L A S D ENGIlVEERING CHEJfIXTRY
55
that the rate of the reaction quickly drops again as one might expect in view of the fact that cobalt driers cause surface hardening. The reaction curves for lead driers fall between that for the oil alone and that for the oil containing manganese driers. Experiments 9 and 10, containing 0.3 per 'cent of lead as linoleate, were intended merely to check one another. Comparison of thcse results with those for experiment 11 shows that there is no marked difference between the effect of 0.3 and 0.1 per cent of lead. The effect of different acid radicals is illustrated by runs Table I-Oxygen Absorbed by Drying Oils before Gelling at 160' C. EXPT. MATERIAL GELLING TIME OXYGENABSORBED 12, 13, and 14 (Figure 4). The synthetic triglycerides of Cc./lO g. oleic and of linoleic acids, and of the mixed fatty acids of linseed Hours .Ifin. oil % b!. umt. oil after they had been distilled in z~ucuo,chilled, and filtered, 727" 10 39 5 55 1 Linseed oil 1 10 29 5 55 720 2 Linseed oil 1 were studied. Here again one finds smaller differences than 6 09 697 6 9 97 3 Linseed oil 2 one might have expected. Triolein oxidizes at a rate not 16 864.2 12,35 5 4 Linseed oil 2 far below that for linseed oil. I n order for it to gel, however, 14 12.85 5 899.6 5 Linseed oil 2 9 20 828.0 11.83 about 50 per cent more oxygen is required. Since the aver6 Linseed oil 2 (50% Ne) 4 18 869.9 12,28 7 Linseed oil 2 + 0.033% M age rate at which this extra oxygen is consumed is low, the 3 57 895.7 12,80 8 Linseed oil 2 + 0.032% c o 42 12.97 4 907.8 9 Linseed oil 2 + 0.30% Pb time required for the oil to gel is more than double that for 32 4 899.8 12.71 10 Linseed oil 2 4- 0.30% Pb 17 5 917.3 13.10 linseed oil. If we leave out of consideration the initial 11 Linseed oil 2 + 0.10% Pb 12 1296 08 18.50 12 Oleic triglyceride and final rises in oxidation, we notice that the curves are 13 Synthetic mixed triglycerides 4 06 $28.0 11.83 of linseed oil straight lines. The little rise at the end is probably due to 55 186.7 2 11.38 14 Linolenic triglyceride 21 1076.0 7 a tendency to froth just before gelling, with the result that 15.37 15 Linseed free fatty acids 16 Pentaerythritol ester of linothe average area of the oil surface exposed to the oxygen 2 17 618.8 8.84 lenic acid 17 Linseed oil 2 + 15% free is increased. If we extrapolated the graph for oleic tri837.0 4 59 11.96 f a t t y acids glyceride it would cut the axis a t 1760 cc., and this pre18 Effect of 7 hours' extra heating on pentaerythritol ester of sumably represents the total volume of oxygen that could be 372.0 5 31 40 8 linolenic acid rl At O 0 C. and 760 m m . consumed by 10 grams of triolein did not gelation intervene and prevent thorough and rapid exposure of the oil to the The first three experiments were performed before the oxygen. platinum wire had been sealed into the apparatus between B1 and B3. It will be noticed that the total oxygen consumed is markedly less than in experiments 4 and 5. The difference represents the volume of oxygen required for the combustion of the organic gases which escaped destruction by the sulfuric acid and the soda lime. Analyses indicated that approximately 120 cc. of the combustible gas accumulated in the apparatus (which has a volume of 590 cc.) by the end of the experimenti. e., when the oil gelled. It will also be noticed that the time required for gelation is also greater for experiments 1 to 3 than for 4 and 5 . This is probably due to the fact that the rate of absorption of oxygen by the oil itself is decreased by its dilution by the gas. This assumption is confirmed in experiment 6 in which 50 per cent nitrogen was used in the gas stream, with the result that the rate of the reaction dropped something like 50 per cent also (Figure c c "9 O.,y9." f.& up 3). The irregularities in the curve for this experiment are Figure 3 due to the difficulty in maintaining a uniform concentration of oxygen by the addition of fresh oxygen to the circulating The apparatus as built to study rates of oxidation was sealed glass to glass. Ground-glass joints were coated with gas stream. A rough analysis of the gas which is not destroyed by demotinsky cement. It did not lend itself, therefore, to sulfuric acid or soda lime showed it to contain no carbon mon- determination of weight of volatile oxidation products or oxide, no illuminants, and only traces of carbon dioxide. gain in weight of the oil in the oxidation vessel. This inWhen burned in an explosion pipet it yielded some carbon formation is, however, very desirable in order to get a more dioxide and water. It is therefore probably a mixture of complete picture of the extent to which oxygen absorbed hydrocarbons. entered into volatile oxidation products, and to what extent The influence of manganese, cobalt, and lead linoleate it remained in the gelled oil a t the end. driers was studied in experiments 6,8,9,10, and 11. The reI n order to get this information, a t least to an approximate sults were surprising in that the driers proved to have relatively extent, auxiliary experiments were run as follows: Ten little effect upon the reaction. Not only was the total grams of each of four of the materials mentioned in Table amount of oxygen required for gelation nearly the same, I were heated in a paraffin bath to 160" C. in Pyrex tubes but the rate of the reactibn was only slightly altered, It of approximately the same bore as that of the oxidation is true that with the cobalt drier the rate more than doubled vessel in the main apparatus. Oxygen was bubbled through that a t the beginning of the experiment. This may, how- each tube a t the rate of 30 cc. per minute and the volatile ever, be due to a merely surface action of the drier opera- products were caught in a train consisting in order of (1) tive only upon the comparatively stationary film of oil on a trap filled with glass wool; (2) calcium chloride; (3) asthe sides of the reaction vessel immediately above the sur- carite; (4) a Pyrex combustion tube containing coiled reface of the oil. If this is the case, it is interesting to notice sistance wire heated to redness to burn hydrocarbons,
in Figures 3 and 4, in which the rate of oxygen consumption is plotted against total oxygen consumption rather than against time. Different oils and related materials, using a 10-gram sample of each, were oxidized in the apparatus at 160" C. and the total oxygen required to cause the sample to gel was determined. The time required was also noted. These results are summarized in Table I.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
56
aldehydes, etc.; (5) calcium chloride; and (6) ascarite tubes to catch the products of combustion from (4). The tubes containing the esters being oxidized were weighed a t the start and after the oil had gelled. Ultimate analyses of the solid gels a t the end were also obtained. The primary data, together with quantities calculated from them, are give: in Table 11. Table 11-Volatile
Oxidatlon Products from Drying Oils a t 160° C. PENTAERYTHRITOL ESTEROF
Gelation time Oil at start Gel at end Net increase Trap
coz
Ha0 COZ from combustion H ~ Ofrom combustion
Ultimate analyses"
OLEIC LINOLENIC LINOLENIC LINSEED TRIGLYCERIDE TRIGLYCERIDEACID OIL 2 24 hrs. 30 min. 5 hrs. 15 min. 3 hrs. 20 min. 8 hrs. 45 min. Grams Grams Grams Grams 9.9974 9.3574 9.9968 9.9944 10.0791 9.7512 10.2551 10.2093 0.0817 0.2938 0.2583 0.2149 0.1107 0.0869 0.0868 0.0662 0.0441 0.0527 0.0933 0.2628 0.4159 0.1130 0.0952 0.2060
0.3123
0.2044
0.0968
Vol. 23, No. 1
The percentage of oxygen absorbed up to gelation varies within the rather narrow limits 11.38 to 13.10 for all triglycerides except triolein. This embraces variations in the degree of unsaturation and takes in the effect of moderate percentages of driers. This was somewhat unexpected. It is true that the linolenic triglyceride, with its greater number of double bonds, did exhibit a slightly greater polymerization effect than the natural oils and gelled with the lowest oxygen adsorption, 11.38 per cent. Also, as expected, the driers did facilitate oxidation and reduce the time required for gelation. I n so doing they disturbed the balance between oxidizing the polymerizing reactions in favor of the oxidizing reactions. The percentage of oxygen taken up is
0.1559
0.1723 0.1198 0.0499 0,0666 Found Calcd. Found Calcd. Found Calcd. Found Calcd. 70.40 69.79 70.03 70.66 75.60 75.49 69.45 70 22 10.37 10.61 9.21 9.50 9.93 10.13 9.09 10.06 0% 19.23 19.59 20.76 19.85 14.47 14.37 21.46 19.71
Oz in final gel
in original oil On united with oil Total Ot absorbed 02 i n v o l a t i l e products, b y difference C in volatile product 0 2
HZ i n volatile product
Grams 1.940 1.085 0.855 1.850
Grams 2.021 1.030 0,991 1.124
Grams 1.483 1.089 0.394 0.783
Grams 2.048 1.093 0,955 1.260
0.995
0.133
0.391
0.305
0.157 (2.05%)
0.0678 (0.93%)
0.0408 (0.52%)
(0.87%)
0.0654 (5.52%)
0,0258 (2.59%)
0.0161 (1.53%)
0,0303 (2.69%)
0.0681
On i n v o l a t i l e product by determination 0.941 0.378 0.238 0.424 a Ultimate analysis figures are for oil coni:aining 0.03per cent cobalt.
Owing to difference in the shape of the vessels and the location and bore of the inlet tube, the times required for gelation are greater in the auxiliary experiments, and the results are therefore not strictly comparable. Even with the longer times, however, the results indicate that most of the oxygen remains in the gelled oil. This varies from 46 per cant in the case of oleic trigylceride to 88 per cent for linolenic triglyceride. It is interesting that the latter with its greater number of double bonds caught and retained the largest amount of oxygen. Discussion of Results
I n experiment 6 the gas circulated was a mixture of approximately 50 per cent oxygen and 50 per cent nitrogen. The time required for gelation was 9 hours 20 minutes instead of 5 hours 15 minutes. This is as would be expected. The oxygen taken up by the oil a t the gelation point is 5.7 per cent less. This is not a great difference, but is sufficiently beyond the difference in duplicate experiments to offer additional evidence that even a t 160' C. polymerization reactions are also taking place to some extent, and to suggest that in the ordinary processes of heat-bodying of oils for enamels, varnishes, and similar products there is a balance between at least these two types of reactions. Variation of factors such as temperature disturbs this balance. Two batches of the same oil cooked to the same physical test-e. g., viscosityat different temperatures do not differ simply in color or other noticed effects such as time required to make them, but differ to some extent fundamentally in composition as affected by differing balance or distribution of the various types of reactions occurring. This premise is c o n h e d by other data in this paper (runs 16 and 18) and by other data from this laboratory.
cc
*'Y?F"
er*sr
up.
Figure 4
therefore slightly greater. However, in contrast to these small variations with the glycerides, the larger and more complicated molecules of pentaerythritol ester gelled in much shorter time and much less oxygen was required for it to reach the gel point. As mentioned, this suggests that even a t 160" C . a certain amount of purely heat polymerization of either the raw or the oxidized oil molecules is taking place. To investigate this more fully a sample of the pentaerythritol ester of linolenic acid was oxidized in the usual manner until it had absorbed 334 cc. The apparatus was then swept out with nitrogen and the oil subjected to 7 hours' heating at 160" C. while nitrogen was circulated through the oil in place of oxygen. At the end of that time it had not gelled. The nitrogen was then swept out and the system filled with oxygen and the experiment continued. Gelation quickly resulted. The 7 hours' extra heating nitrogen at 160' C. reduced the total amount of oxygen required for gelation from 618.8 cc. to 378 cc. These results seem to offer evidence that gelation ensues when a certain size or degree of complexity of the molecules is reached and that the influence of degree of unsaturation, degree of oxidation, presence of driers, and other factors is secondary. Gelation is affected by these factors in that they determine the building of molecules of sufficient size, complexity, and perhaps polarity to undergo the phenomenon we call gelation. It will be observed that in nearly all the curves for rate of oxidation there is slight rise at the start. This at first suggests that in the early stages of oxidation substances are formed in the oil which exert catalytic effect on the subse-
57
INDUSTRIAL AND ENGINEEBING CHEMISTRY
January, 1931
quent oxidation. However, the increase in rate of oxidation extends for only a short part of the oxidation. It is believed, therefore, that this effect is explained more logically on the basis that the natural antioxidants present in small amount in the natural oils are oxidized or removed rapidly at 160” C. The rate of oxidation increases until their influence is destroyed and then decreases steadily as the ethylene linkages of the oils are used up. The curves have slight undulations, but in general may be taken as straight lines down to the gel point. After this point is reached the oxygen is not distributed through the oil, but “channels.” The rate of oxidation therefore decreases. From the nature of the curves it is felt, therefore, that the data do not support the autocatalytic theory of oxidation as far as bulk oxidation of the oil a t 160” C. is concerned. The relatively pure linseed fatty acids absorbed oxygen much faster than the glycerides or other esters of these acids do. The rate fell off more rapidly, however, which is shown as a much steeper slope if the results are plotted and the time required for the acids to gel is 2 hours longer than that for the oil itself. Also the percentage of oxygen taken up is the greatest of all the runs made. The free acids are of course much smaller molecules to start with. More building up is needed to arrive a t molecules complicated enough to gel. More oxygen absorption is needed for this increased building. The large percentage of oxygen absorbed and the long time Tequired for gelation are therefore explainable in accord with the premise that gelation follows as a consequence after a certain size or degree of complexity of the molecules has been attained. Comparison of runs 17 (15) is suggestive. We have just noticed that the 99 per cent free fatty acids required a long time and a great oxygen absorption before they gelled, but a mixture of oil and free linseed fatty acids containing 15 per cent of free fatty acids and 85 per cent of oil gelled more rapidly than oil alone. The percentage of oxygen absorbed is also less. This indicates that at least a small percentage of fatty acid exerts a stimulating effect on gelation, provided enough glycerides are present to develop the gel structure. Metallic driers, without seriously changing the oxygen absorption, have the same effect of speeding up time of gelation. This may be an attribute of certain polar bodies. This observation is therefore being extended to other materials and other percentages of these materials. It is well known that the acid value of an oil rises during heat-bodying and that the final acid value is subject to considerable control. If gelation is dependent on the percentage of free fatty acid, many isolated practical observations and apparently unrelated phenomena may be explained and controlled. The data for ultimate analyses are suggestive. Oleic triglyceride contains 10.85 per cent of oxygen; the gel formed from it, 19.23 per cent. The difference, 8.38 per cent, corresponds closely to the weight of oxygen required to saturate each ethylene linkage with the two atoms of oxygen and form the peroxide linkage:
ester, gelation intervened before each molecule of linolenia acid had acquired one peroxide linkage as an average. Figures are given in Table I1 showing the calculated ultimate analyses corresponding to an absorption of two atoms of oxygen by each molecule of acid in the case of the three glycerides. The figures for the pentaerythritol ester corre spond to absorption of only three atoms of oxygen per molecule of ester. The four oils for which data are given in Table I1 all showed slight net gain in weight a t gelation. If iilms of drying oil on panels were dried by oxidation in an oven a t 160” C., they too would probably show this increase in weight. However, as indicated by the other data, this would not tell the complete story or in any way indicate the extent to which other reactions were going on. I n the case of oleic triglyceride 7.57 per cent of the carbon and hydrogen of the original oil escaped as volatile products and only 46 per cent of the total oxygen absorbed remained in the oil. This is probably due to the fact that the oxidation had to be continued for 24 hours. With the other esters, where gelation ensued in shorter time, the losses by oxidation are much lower, amounting to only 2.05 per cent in the case of the pentaerythritol ester. The weight of oxygen that went into volatile products is calculated by two methods. They are not in close agreement. I n two cases those “by difference” are greater than the “determined” figures, in the other two cases they are smaller. The method is still susceptible of refinement, but the results seem to tell the story of what happens a t this temperature. The present data do not show just how the molecules are linked in the gel-i. e., whether they are simply held together by secondary forces as represented by the scheme
or whether there is coupling of the molecules by primary 1inkages:as indicated by some scheme such as: R
I
H-C-0-0-C-H H-&-0-0-C-H
I
Ri
R
I
I
RI
The thick oils and gels liberate iodine from potassium iodide in acid solution. Peroxide groups are therefore present. Acknowledgment
H
H
The writers wish to acknowledge the help of William S. McCarter and A. E. Rheineck, Archer-Daniels-Midland, and William 0. Goodrich Fellows at Lehigh University, in securing data for Table 11, and also the help of Professor N. S. Hibshman in improving the design of the electrical circuits.
I
1
Literature Cited
I
1 -c - c0 - 0
Further, gelation intervened in the cases of linolenic triglyceride and of natural linseed oil when enough oxygen had been taken up to form one peroxide linkage on each molecule of acid. With these two substances two-thirds and one-half of the ethylene linkages, respectively, would still remain unsaturated except for other effects. I n the case of the larger, more complicated molecule of pentaerythritol
(1) Chataway, J . SOC.Chem. I n d . , 47, 167T (1928). (2) Chatterji and Finch, J . Chem. Soc., 121, 2464 (1925). (3) Chatterji and Finch, J . Soc. Chem. I n d . , 46, 332T (1928). (4) Coffey, J . Chem. Soc., 119, 1152 (1921). (5) D’Ans, Z . angew. Chem., 41, 1193 (1928). (6) Fahrion, I b i d . , 23, 722 (1910). (7) Funnel and Hoover, J . Phys. Chem., 31, 1099 (1927). (8) Long, Kittelberger, Scott, and Nevins, IND. ENG.CHBM.,21, 950 (1929). (9) Morrell and Marks, J . Oil Colour Chcm. Assocn., 12, IS3 (1929).
