INDUSTRIAL A N D ENGINEERING CHEMISTRY
April, 1930
plugs. These are extremely heavy current densities and are inch in about sufficient to corrode cast iron to a depth of 12 years, assuming 100 per cent corrosion efficiency and also assuming that these currents continue. On specimens buried in the earth current densities twice as great as the above have been found. Tests made about 12 hours later showed that the current had decreased and that it was due directly to a decreased difference of potential between the plugs and the pipe, from 0.087 and 0.093 volt to 0.038 volt for each plug. Potential measurements of the brightened cast iron and the oxidized pipe to the copper sulfate reference electrode showed that the potentials of the brightened iron plugs had remained stationary in one case a t -0.730 volt and in the other case had showed very little change, from -0.720 volt to -0.730 volt. The potential of the oxidized pipe had changed materially, from -0.620 volt to -0.690 volt, and it was this change that caused the reduction of the difference between the brightened cast iron and the pipe. This change mas probably due to polarization, which in turn was probably due to the collection on the surface of the pipe of galranic current, not only from the plugs, but from innumerable other small galvanic cells on the surface, as evidenced by the fact that cast-iron pipes not having artificially brightened surfaces go through the same cycle. Potential-difference measurements were now made in the jelly surrounding the pipe with the aid of two copper sulfate electrodes and the earth-current meter. The current discharging electrolytically from the plugs had decreased to such a low value, however, that the equipotential and current stream lines drawn from these particular results did not give a good demonstration. Distinct equipotential and current stream lines were to be seen, but they were radiating from other anodic points on the pipe. Examination of the discolorations in the jelly showed that the brightened castiron plugs were entirely covered with blue, indicating the dissolving of iron and the passage of electricity to the solution. The remaining areas of the pipe were surrounded, generally, by a pink discoloration, indicating an alkaline condition of
341
the solution caused by the collection of current. A few other small blue spots appeared, indicating other anodic areas. The fact that the currents died down in the above ferroxyl test may be taken as a good indication that these galvanic currents are transient and of no serious consequence. The decrease of current was due to the change of potential in the negative direction due to polarization. Long-time tests have shown, as previously stated, that after several months a depolarization sets in and the galvanic difference of potential is again restored. When this takes place the extent of corrosion is probably a matter of the formation of protective films over the surfaces of the anodes. Should proper films form, corrosion will probably cease, while should it not form, we see no reason why the iron should not continue to go into solution from ordinary electrolysis caused by galvanic forces. Remedies for Galvanic Corrosion
This general quest:m of corrosion is important to utilities, as in many communities the railway, water, gas, and power systems are owned by different interests and the matter of differentiating between soil corrosion and electrolysis comes up very frequently. Remedies for stray-current electrolysis conditions, while in many cases not simple, are not, however, very difficult, but to overcome the galvanic action on a system of uncoated gas or water mains which have already been laid is rather difficult. Electrolysis drainage, or the connection of underground metallic structures to the negative busses of railway substations, a measure which was applied to the water mains in New Orleans primarily to protect them from stray currents, is not only accomplishing its purpose, but is also protecting a large part of the system from the ravages of destructive galvanic currents. The drainage causes a collection of current which counteracts the discharging galvanic currents. Literature Cited (1) McCollum and Logan, Bur. Standards, Tech. Paper 551 (1927).
Autoxidation of Corn Oil as Related to Its Unsaponifiable Constituents’ H. A. Mattill and Blanche Crawford D E P A R T M E N T OF CHEMISTRY, S T A T E UNIVERSITY OF
HE spontaneous oxida-
IOWA, IOWAC I T Y ,
IOWA
and the production of a great The keeping qualities of fats and oils are primarily tion or autoxidation of dependent upon the relative proportions of “prooxivariety of partial oxidation fats and oils is a corndants” and “antioxidants” which they contain. Heatproducts, some of which may plex and puzzling process of treated oils often show a much shorter induction period in turn be or become perinterest both in thetechnology than untreated oils. Observationson corn oil in various oxides. The reaction is thus autocatalytic, and when the of,drying o i l s a n d in t h e stages of preparation relate the antioxidizing sterols p r e p a r a t i o n o f industrial and the products of heat treatment with susceptibility values for oxygen consumed are plotted against time the and edible fats. It is deto oxidation. usual form of parabolic curve p e n d e n t in t h e f i r s t i n stance upon the presence of one or more dvuble bonded car- for such reaction is obtained. lions. According to the conceptions developed by Engler Prooxidants and Antioxidants and Weissberg (b), Powick ( I d ) , Kerr and Sorber (9), Eibner and Pallauf Tschirch (16); and Holm, Greenbank, and But the mere presence of unsaturated carbon is of less Deysher (8),peroxide-like substances (ozonides, “moloxides”) moment for the process of oxidation than is that of subare formed by the addition of molecular oxygen a t the double stances which initially either accelerate or retard the reaction. bond. The further oxidation of these more easily oxidizable The compounds which favor the reaction are presumably compounds causes the rupture of the chain a t the double bond similar to the initial products just mentioned, substances of potentially high oxidizing ability. Contact of such a peroxide 1 Received February 14, 1930.
T
a),
342
INDUSTRIAL A N D ENGINEERING CHEMISTRY
with an unreactive glyceride brings about oxidative changes which molecular oxygen alone cannot accomplish. Autoxidation of fats thus consists of two stages; the active uptake of oxygen is preceded by a shorter or longer interval known as the induction period, during which the compounds of high oxidizing potential are accumulating in amount sufficient to start the interaction with atmospheric oxygen. Scarcely measurable amounts of oxygen are consumed in the preparation of the oxidizing catalysts, and their presence and manner of origin in fats are as obscure as their chemical nature. Eome of the conditions which favor the autoxidation of fats are illustrated and discussed by Holm, Greenbank, and Deysher (8). These authors also consider some of the even more interesting agencies whose effectis to prolong the induction period, and ahich are variously known as “antioxygens” or “antioxidants.” Whether their action is explained on the basis of the theory of “negative catalysis” of Moureu and Dufraisse (15) or that of the chain reactions of Alyea and Backstrom (I), these antioxidizing substances apparently either form compounds with the peroxides (prooxygens) or suffer direct or induced oxidation a t their hands, thus preventing their accumulation in amounts sufficient to allow active oxidation. Theory requires that antioxidants be themselves easily oxidizable and their effectiveness is limited to the induction period. Once absorption of oxygen has begun, the rate is uninfluenced by their presence and is dependent only on the chemical nature of the fat undergoing oxidation. Various antioxidizing substances have been studied, especially in the rubber industry. Those concerned with fats probably contain only carbon, hydrogen, and oxygen, and the classical example is hydroquinone. Unpublished observations in this laboratory indicate that the factors which determine the effectiveness of an antioxidant of this type are the number and especially the location of the hydroxyl groups in the compound. Their number is indicated in part by the acetyl value of the fat, which in the absence of hydroxy fatty acids like ricinoleic and of mono- or di-glycerides has its only origin in the unsaponifiahle portion of the lipidnamely, in the sterols. The relative ease of oxidation of a fat, as expressed by the length of the induction period, is thus a measure of the “prooxidants” and “antioxidants” which it contains. If a fat or oil when examined has already “lived through” a portion of this induction period or has been exposed during manufacture and storage to conditions favoring the production of such catalysts, its susceptibility to oxidation will be proportionately increased. If, on the other hand, the fat contains antioxidants, these will decrease the susceptibility to oxidation in proportion to their amount and effectiveness. In another connection (la)it has been pointed out that the oxidative destruction of the fat-soluble vitamins A and E in experimental diets containing animal fats such as lard and cod-liver oil is more rapid than when these fats are replaced by vegetable oils of equal or greater unsaturation, and in agreerent mith this the acetyl values of the latter are considerably greater than those of the former, thus suggesting the presence of antioxidizing sterols in the vegetable oils. Materials and Methods
The keeping qualities of vegetable oils as marketed are generally less satisfartory than those of the oils obtained from their natural sources by the aid of organic Polvents and without heat treatment, and it seemed desirable, therefore, to examine a vegetable oil in the various stages of its manufacture with particular reference to the induction period, its sterol content, and acetyl value. For this purpose a series of corn oils was made available through the courtesy of the
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Staley Manufacturing Company. These oils included a petroleum ether extract (not above 50” C.) of the corn germ and five samples from the usual manufacturing process beginning with the crude expeller oil and ending with the final market product. For the measurement of the induction period a modification of the apparatus used by Greenbank and Holm (6) was employed. Erlenmeyer flasks containing usually 10 grams of the oil with oxygen were immersed in a calcium chloride solution maintained a t 70” C. The flasks were connected to open manometers through a mercury seal, and platinum contacts in the manometers were connected to signal magnets writing on a slow kymograph. By means of hourly contacts from a clock a graphic record was thus secured which indicated the first diminution in volume due to absorption of oxygen. Absolute values for the amount of oxygen absorbed were not obtained, as the relative length of the induction period was of primary interest. The method used for the quantitative determination of the unsaponifiable constituents (sterols) was that described by Kerr and Sorber ( I O ) and the acetyl value was determined by the method described by Woodman (1‘7). The acetyl values of the sterols were determined in the same manner. Results and Discussion The data secured on the various oil samples are compiled in Table I. The figures for induction periods are the average of as many as fifteen determinations on each sample, this number being necessary because of the great variability due in part to limitations in the apparatus and in part to unknown factors. The other figures represent satisfactory duplicate determinations. Table I-Experimental
OIL
SAMPLE
Data
ACETYL VALUE UNSAPONIOF UNFIABLE ACETYLSAPONIINDUCTION CONSTITU-VALUE FIABLE PERIOD BNTS OF OIL MATTER Hours Per cent
TREATMENT^
0
Petrol ether extraction of corn germ below 50’ C. 40 2.04 6.3 103 Crude corn oil from exI pellers, 93’ C.for 5 t o 10 minutes, 175’ C. for 1 or 2 seconds 10.5 1 2.05 12.0 97.5 I1 I neutralized f 46-68’ C.for 1 hour 8.3 1 1.72 7.05 103 I11 I1 with fuller’s earth and filter aid, 60’ C. in 6.8 vacuum 7 0.75 1.52 IV 111 winterized by 1’ C. for 2 days, cold filtration 7 . 0 =t0 . 7 5 1 . 4 0 6.45 V I V deodorized by vacuum distillation, 5 hours, max. 200’ C. 5 * 1 1.27 5.6 107 Or Abbreviated from a description kindly furnished by Mr. Durkee. superintendent of oil refinery, A. E. Staley Manufacturing Company. f
f
-
..
It is obvious that the susceptibility to oxidation as measured by the induction period increases steadily throughout the manufacturing process; this is particularly notable following the steps that involve rather severe heat treatment (I and V), the greatest difference being between the cold extracted oil (0) and the crude oil from the expellers (I). Contrary to the usual observations on induction period, the oxidation of the unheated oil proceeded very slowly, while the factory samples, once active oxidation had begun, absorbed oxygen a t practically equal and gradually increasing rates. The figure for the induction period of the final product (V) is in substantial agreement with that reported by Triebold ( l 5 ) , who studied the induction periods of a number of edible fats a t 95” C. His corn-oil period was 0.75 hour. Unpublished observations from this laboratory indicate that the temperature coefficient of this thermal induction period reaction is between 2 and 3.
April, 1930
I-VD USTRIAL A N D ENGINEERING CHEMISTRY
To answer the question as to the nature of the change which took place and which caused a continuous decline in the length of the induction period, the unsaponifiable constituents were determined. The figures obtained are in good agreement with those reported by Anderson and Moore ( 2 ) . Surprisingly enough, the amounts of sterols in expeller oil and in the cold extracted oil were alike, notwithstanding the marked difference in induction period of the oils. The two sterol samples were very different in appearance. That from the unheated oil consisted largely of white crystals typical of sitosterol, while that from the expeller oil was an amorphous material, reddish brown in color. Apparently the treatment of the oils, while not changing the amount, nevertheless greatly changed the character of the sterols, depriving them of their crystalline character and ostensibly of a large part of their antioxidant power. Another explanation for the shortening of the induction period is that the heat treatment produced furthw amounts of more readily oxidizable fats and increased the amount of the “peroxides” present, such that an impaired antioxidant had to cope with a greater susceptibility to oxidation. That peroxides are present in the heat-treated oils was easily shown by the potassium iodide-starch test (1);). All of these oils (I to V) produced noticeable bluing of the starch. The cold-extracted oil (0) developed a trace of color much later, even later than the blank test. In the oil samples I to V the gradual reduction in length of the induction period rather closely paralleled the decreasing amounts of unsaponifiable material. Since the acetyl value is a direct measure of the hydroxyl groups present, the data on the acetyl values of the oils should be significant, but the figures on samples 0 and I are confusing, particularly the latter, which is almost double that of any others. As pointed out by Lewkowitsch (11). partially hydrolyzed natural oils and fats contain small quantities of mono- and di-glycerides which are capable of exchanging the hydrogen of the alcoholic hydroxyl group for an acetyl group. The smaller acetyl value of the neutralized oil (11) indicates that the mono- and di-glycerides have btben largely removed in this step. It is interesting that the acetyl value of the unheated oil (0) is lower than that of any of the commercial samples except the final product (V) and that, excepting the expeller oil, there is a gradual decline in this value with the progress of the manufacturing process somewhat parallel to the induction period. This further suggests that the acetyl value of the oil is not a true measure (of the hydroxyl groups in the sterols. To determine what changes the sterol portion may undergo, a sufficient amount of this was prepared from sevwal of the oils for acetyl determinations. As seen in the table, the acetyl number of the sterols suffered little change during the various procedures. Taken in conjunction with the physical characteristics of the unsaponifiable constituents obtained from the cold extraction and from the expeller oil, the fact that the amounts of sterol and their acetyl values are practically identical suggests that they suffer some intramolecular change as a result of the heat treatment. Their antioxidizing capacity may be reduced thereby and the presence of larger amounts of easily oxidizable materials assists in the shortening of the induction period. In this connection the behavior of ergosterol under the influence of ultra-viol& radiation requires comment. An exposure of a few seconds suffices to transform a small portion of the sterol into vitamin D. Recently a peroxide test has been proposed (5) t o dtxmonstrate this tramformation. The hydroxyl group plays no part in this reaction, as is proved by the activatability of various esters of ergosterol. The double-bonded carbons are necessary, as shown by the inactivity of the saturated sterol after irradiation.
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Ultra-violet radiation, as shown by Holni and his coworkers (8)is a powerful agent in reducing the induction period of a fat. Relatively short exposure of these corn-oil sterols (among them ergosterol) to ultra-violet light produces peroxide-like materials. A thin film of the sterol from sample 0 was exposed on a microscope slide to a Hanovia laboratory lamp a t a distance of 12 inches (30 cm.) for 15 minutes, half the slide being shielded. Treatment of the slide with starch-potassium iodide revealed the line of the light shield. The photoelectric method of measuring the induction period of fats, recently developed by Greenbank and Holm ( Y ) , and the excellent agreement between thermal and light effects on induction period provide a striking confirmation of the theories of Alyea and Backstrom (1). Whatever the molecular rearrangement here involved may prove t o be, it is clear that ergosterol mag undergo a change toward greater oxidjzability without involving the hydroxyl group. The mixed sterols of corn oil may thus by internal rearrangement lose some of their antioxidant capacity by increase in “prooxidants” without any change in the acetyl value. The proof that the antioxidant effect of the corn-oil sterols resides in the hydroxyl group remains to be given. This consisted in showing that the addition of a small amount of the sterols to an autoxidizable fat appreciably prolonged the induction period over that of the fat without such addition, while the acetylated sterols had no such effect. The results are given in Table 11. Table 11-Effect
of Adding Sterols to Fat on L e n g t h of I n d u c t i o n Period INDLCTION PER100 AT 70’ C .
SAMPLE
Hours 5 grams Same Same Same
lard, 10 drops cod liver oil of sterols of corn oil 0 acetylated sterols regenerated sterols
+ 10 10 mg mg + 10 mg +
lard, 10 drops cod-liver oil + 100 mg of sterols of corn oil 0 + 100 rng acetylated sterols
5 grams Same Same Same
+ 100 mg
regenerated sterols
10 grams lard Same 500 mg of sterols of corn oil I Same with 500 mg acetylated sterols Same 500 mg regenerated sterols
+ +
7 10 7 10
5 5 5 0
4 118 5 73
5 0 0
0
14 0 170 0 3 0 83 0
These figures confirm the antioxidant properties of the sterols of corn oil, and prove that their efficiency resides in the hydroxyl group. The failure of the regenerated product to prolong the induction period to the extent that the original substance does is probably due to the development of more easily oxidizable substances during the heating incident to acetylation. Examination of various fractions of the sterols obtained from wheat germ and lettuce oils is in progress and indicates that the antioxidant effect resides in the portions that are not precipitable by digitonin. Conclusions
The susceptibility of corn oil to spontaneous oxidation increases with the progress of manufacture and commercial purification. This change, as measured by the shortening of the oxidation induction period, is in general parallel to the decrease in amount of sterols which the oil contains. Among the sterols are compounds which have an antioxidant action, an action which disappears on acetylation. Oil extracted by an organic solvent is much less susceptible t o oxidation, although its content of sterols and their acetyl value are the same as found in crude expeller oil. The final trade product has less satisfactory keeping qualities, partly through loss of antioxidizing sterols and partly because of the exposure to high temperatures, which causer the development of easily oxidizable substances of peroxide nature in both trjglycerides and sterol..
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Literature Cited (1) (2) (3) (4) (5) (6) (7) (8) (9)
Alyea and BackstrBm, J . A m . Chem. SOL.,61, 90 (1929). Anderson and Moore, Ibid., 4S, 1944 (1923). Bond, Brit. M e d . J . , 1927, No. 3483, 637. Eibner and Pallauf, Chem. Umschau, 32, 81, 97 (1925); through C. A , , 19, 2420 (1925). Engler and Weissberg, Ber., SI, 3046 (18981, and later papers. Greenbank and Holm, IND. EKG. CHBM.,17, 625 (1925). Greenbank and Holm, I b i d . . Anal. Ed., 2, 9 (1930). Holm, Greenbank, and Deysher, IND.END. CHEM.,19, 156 (1927). Kerr and Sorber, I b i d . , 16, 383 (1923).
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(10) Kerr and Sorber, J . Assocn. Oficial Agr. Chem., 8, 90 (1924). (11) Lewkowitsch, “Chemical Technology and Analysis of Oils, Fats, and Waxes,“ Vol. I, p. 437. (12) Mattill, J . A m . M e d . Assocn., 89, 1505 (1927). 31 ‘13 (1926). (13) and Dufraisse8 (14) Powick, J . Agr. Research, 26, 323 (1923). (15) Triebold, Thesis in Agricultural Biochemistry, University of Minnesota, 1926 (16) Tschirch, Ckem. Umschau, 32, 29 (1925); through C. A , , 19, 1557 (1925). (17) Woodman, “Food Analysis,” p. 167 (1924).
Volatilization of Phosphorus from Phosphate Rock Robt. D. Pike 4069 HOLLIS ST., EYRRYVILLR, CALIF.
11-Experiments in Volatilization of Phosphorus and Potash in a Blast Furnace1 A detailed description is given of two continuous runs of an experimental blast furnace supplied with an oxygen-enriched blast. In one run the furnace charge consisted of phosphate rock, a siliceous flux, and coke; and in the second run the siliceous flux was replaced by a potash-rich flux. The average extraction of PzOswas about 70 per cent, and of K,O, 47 per cent. Further experimental work with the slags on a small scale led to the conclusion that, with a proper furnace design and correctly proportioned slags, extractions of 97 and 92 per cent of P106and KzO, respectively, can reasonably be expected. A good slag to use closely resembles Equipment
CROSS SECTION of the experimental furnace is shown in Figure 1. The general arrangement of apparatus is shown in Figure 2. The breast of the furnace with a 200-pound slag buggy in place is shown in Figure 3. The phosphate rock, coke, and flux were charged by hand through a door in the top of the furnace and the shaft was kept approximately full of charge. This left a large empty chamber a t the top into which air for combustion of phosphorus and carbon monoxide was blown in two semi-tangential streams. Sufficient air was introduced to burn all the carbon monoxide to carbon dioxide and all the phosphorus to phorphorus pentoxide, That portion of the top gases which went to the precipitator was humidified by the introduction of a little steam. The major part of the gas passed up through a stack issuing from the top as a dense cloud of phosphoric acid. (Figure 4) The flow of oxygen and air to the blast was accurately measured by orifice meters and controlled from a central control board. It will be noted that, with the exception of the enlarged top and the central tuy&re, the interior lines of the furnace are of conventional type. The tuysre is a long, water-cooled copper tube extending downwardly along the central axis of the furnace with a four-holed nozzle a t the bottom. The blast of oxygenated air was introduced a t high velocity through these nozzles and a t an angle of about 30 degrees below the horizontal. This type of tuykre was originally designed for the use of highly oxygenated blasts, the idea being to keep the intense heat of combustion away from the walls of the furnace. It was successfully employed with a blast of pure oxygen, but when a cold blast containing 40 to 45 per cent of oxygen by weight was adopted, it was found that
A
1 Received
December 16, 1929.
that employed in an iron blast furnace, and free-running properties should be the chief consideration in determining its composition. The slag should be tapped at from 1450 O to 1500 O C. Under strongly reducing conditions phosphorus will be almost completely evolved from slags of a basic nature similar to those employed in iron blast furnaces, and relatively basic slags are required for the high extraction by volatilization of potash. Blast furnaces operated along the lines indicated by the experiment with hot oxygen-enriched blast for the joint volatilization of P201 and KzO may be expected to operate smoothly and continuously.
this tuy6re was faulty and caused the only persistent operating difficulty that was encountered. This difficulty arose from the fact that as the cold blast entered the heart of the furnace it chilled the dag immediately below it, forming a frozen crust of slag. It was therefore almost invariably necessary to tap the furnace with an oxygen lance, and the top of the crust gradually arose until, a t the end of about 5 days’ continuous operation, the hearth was completely filled with solid slag and a tap could only be effected by burning a hole with the oxygen lance through into the bottom of the bosh. Obviously this operating difficulty pertains to the type of tuy&rc.employed and to the cold blast and not to the process itself. By employing the usual form of side tuv&reswith hot blast containing 30 per cent of oxygen by weight, no trouble of this kind need be expected, nor should there be any more than ordinary difficulties of operation which pertain to the iron blast furnace. I n considering the extractions actually obtained in this experiment, one should give due consideration to the influence of the difficulties of operation which resulted from the type of tuyPre employed. Obviously these were of such a nature as to impair the normal working of the furnace and to reduce the extraction of phosphorus and potash which might otherwise have been reasonably expected. Materials Used
For the purpose of this paper the description will be confined to two continuous runs of 31.5 and 21 hours, respectively. In the former, which will be called run 1, the fluxing material was low in potash and was made up of a mixture of Green River sandstone and firebrick grog; and in the latter, or run 2, Wyomingite was employed as flux. I n other respects the two runs were substantially the same. The analyses of the materials used are given in Table I.
