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most identical distillation curves. At first thought, it might be considered that this difference was due to a difference in chemical constitution. This point was not established in this investigation, however. I n Figure 11F are distillation curves of two gasolines prepared by mixing naphthas in slightly different proportions. The distillation curves are remarkably close. Their volatilities, however, as determined over a temperature range, differ, as shown in Figure 10. This slight difference in the distillation curve, with gasolines of similar chemical constitution, which makes a relatively large difference in the volatility as determined, would indicate that the differences in volatility previously observed for the pairs of fuels of different chemical constitution may be due in part a t least to differences in distillation curves, or of boiling points, which do not appear upon the distillation curves. I n the light of the present information, therefore, i t cannot be stated definitely whether a change in chemical constitution of a fuel, unaccompanied by a change in boiling point, does or does not alter the starting volatility as determined by the present method. On the other hand, it is evident from these data that dis-
VOl. 19, x o . 3
tillation curves of the Engler type cannot be of sufficient accuracy to make dependable estimations of relative volatility, especially a t low temperatures. Probably this is due in part to the fact that a t these low temperatures only the very volatile portion of the fuel is evaporated. This is the portion which either distils over in the Engler distillation as an uncondensed gas, or boils off so rapidly as not to appear clearly in the initial distillation point as recorded in usual practice. Bibliography 1-Eisinger, J . Soc. ;lutomotiue Eng., 18, 147 (1926); 19, 3 (1926). 2-Gruse, I n d . Eng. Chem., 16, 796 (1923). 3--Kennedy, Bur. Standards, Sci. Paper 600 (1925). I--Wilson and Barnard, J . Soc. Automotive Eng., 12, 287 (1923); I i l J . Eng. Chem., 17, 428 (1925). 5-Stevenson and Stark, Ibid., 17, 679 (1925). 6-Sligh, J . Soc. Automotive Eng., 18, 393 (1926); 19, 151 (1926). 7-Burrell a n d Boyd, BUY.Mines,Tech. Paper 116 (1915). 8-Carlson, J . Soc. Automotive Eng., 12, 139 (1923); Lee, I b i d . , 18, 3 (192:1) , Birdsell, Ibid., 14, 267 (1924); Eisinger, Ibid., 16, 69, 333 (1924); Spnrrow and Eisinger, I b i d . , 16, 237 (1925); Eisinger, I b i d . , 17, 52 (192.5).
Spontaneous Heating of Oils' Methods of Testing By Norman J. Thompson INSPSCTION D E P T . , ASSOCIaTED
FACTORY & ~ U T U A LFIREI N S G R A X C E
Chemical methods such as absorption of iodine or of oxygen are not suited to critical examination. The iodine number often has no significance, and the results obtained by absorption of oxygen are subject to uncontrollable errors. The original Mackey method is not suitable for indication except in the case of the more dangerous oils. By increasing the size of the sample to 30 grams, using clean cotton waste carrying an equal weight of oil, more significant results can be obtained with no more attention, even though the test time is longer. The method which in general gives the most information involves the maintenance of a small temperature differ-
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Chemical Methods
There has been a tendency in the past to class various oils on the basis of their iodine numbers; the hazards were assumed to be directly proportional to the iodine values. However, the iodine number does not indicate either the extent or the rate of oxidation except in a general way. For example, the lower the iodine number of linseed oil the more rapid will be its oxidation a t normal temperatures. This is true in nearly every case and can be explained by the fact that oxidation, while decreasing the iodine number, greatly assists further reaction due to the catalytic effect of the October 25, 1926.
ence between the sample and its surroundings. This method clearly shows that certain oils formerly thought to be relatively safe may, under favorable conditions, be more hazardous than other oils which have been classed as dangerous. If the temperature difference is taken care of automatically, the apparatus might be complicated and somewhat expensive. If the regulation is secured manually, the operator's constant attention is required. Regardless of the method employed, results can be interpreted only by comparison with tests on oils of known performance. Furthermore, the conditions under which the oil is to be used must be known in order to indicate correctly the probable hazard from spontaneous heating.
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ONG experience with fires caused by oils such as lard oil, red oil, and wood oil led to grave doubts regarding the value of available methods of testing for tendency to heat spontaneously. Accordingly, a study was made in order to obtain more definite information about existing methods, and, if necessary, to develop a new method which would more closely simulate the very favorable conditions often existing in practice.
1 Received
COMPANIES, BOSTON, M A S S .
oxidation products themselves. Furthermore, substaiices are frequently added to commercial oils which increase the iodine numbers but a t the same time decrease the oxidation rates. Another method of indicating the spontaneous heating or autoxidation of oils is to measure directly the absorbed oxygen. This method, however, is unsatisfactory for critical examination. When samples such as cottonseed oil or oils of even greater heating tendencies are tested by such a method, i t is found that the oxygen absorbed in a definite length of time is closely proportional to the heating rates of the oils as determined in other ways. However, when testing oils such as castor oil or mixtures of cottonseed and mineral oil, it is often found that instead of a gas absorption there is an increase in pressure. This pressure increase is due to the vapor pressures of the oil and of its oxidation products, and is great enough a t temperatures around 100' C. to make unreliable any figures obtained by the absorption method. Since we are most interested in obtaining significant data on oils of lesser heating tendencies than cottonseed oil, this method proves utterly lacking.
March, 1927
INDUSTRIAL A N D ENGINEERING CHEMXSI'RY
3'35
Ordway Apparatus
A New Test Method
Several methods have been worked out to show heating tendencies directly in the form of a rise in temperature. One apparatus using such a method, and which was more or less popular several years ago, is the Ordway. The method employed is essentially the comparison of an oiled sample of cotton waste with an unoiled sample of equal size. Conditions favorable for heating are brought about by placing the samples in an air bath, which it was desired to maintain at 100" C. In the writer's estimation this equipment is of little more than historical interest, because it is only with extreme difficulty that tests can be duplicated un identical samples of oil.
For more general use it is desirable to have available an apparatus in which almost any practical conditions can be duplicated in effect. For example, where a large quantity of oiled fiber is stored, such as in a n.001 warehouse or in the hold of a ship transporting sisal twine, it is necessary to consider the heat-insulating effect of a large mass of material. Furthermore, one might wish to know the hazard connected with the drying of an electric insulating varnish in a baking oven a t 300" F. (149" C.). Accordingly, an apparatus was devised with these cond i t i o n s in view. It consisted of a horizontal oil-jacketed s t e e l tube 2.5 inches inside diameter and 12 inches in length. Two caps, each supplied with nine 3/lo-inch holes for air admission, were p r o vided to fit the ends of the tube. The temperatures of the oil bath and of the sample are indicated by two thermometers. W h e n t e s t i n g oil emulsions i t is necessary to evaporate practically all of the water before any heating can Apparatus for New Test Method b e o b s e r v e d ; consequently, in the comparative tests made in this apparatus the bath temperature chosen was 220' F. (101.4" C.). The sample, 30 grams of clean cot'ton waste into which had been worked an equal weight of oil, was placed in the tube after the bath had reached the test temperature. The bath temperature was then maintained constant until the temperature of the sample exceeded it by 2' C. From this time on, the bath temperahre was kept 2" C. below that of the sample. The temperature difference of 2" C. was selected primarily because this was as close as it seemed advisable to go and not be in danger of heating the sample artificially.
Mackey Apparatus
The apparatus which is in most general use today was devised by hlackey and is manufactured by Reynolds & Branson. Ltd., Leeds, England. This apparatus is essentially a water-jacketed cylinder 4 inches in diameter and 7 inches in height, closed at the top by a cover having a center hole to accommodate a thermometer and also two draft tubes, each approximately 6 inches in length and 0.5 inch inside diameter. One of these draft tubes extends donx into the cylinder and the other extends upwards from the corer.
Samples Used in the Tests
For the tests made in the various equipments described several kinds of oil were purchased, which included the more common vegetable, animal, and mineral oils. Chemical examinat,ion showed these oils to be genuine, unadulterated, free from rancidity, and representative of high-grade commercial products. The values of free fatty acid expressed in terms of oleic acid were: Apparatus for Mackey Test Method
The procedure originally recommended for 1he >lackey apparatus requires a sample consisting of 7 grams of absorbent cotton carrying 14 grams of the oil to be tested. The sample is placed in a wire gauze cylinder about 13/s inch in diameter and 6 inches long, the cylinder being held concentrically in the apparatus by a projection on the inside of the jacketed vessel. The customary procedure is to bring the water bath to boiling. insert the sample into the apparatus, and then take readings of the thermometer a t frequent intervals. If a sample does not exceed 100" C . (212" F.'I wkhin a n hour or 200" C. (392" F.) within 2 hours, the oil is considered safe as far as its tendency for spontaneous heating is concerned.
Pure lard oil (from KO.1 lard) . . . . . . . . . . . . . . . . . . . . . . . . Denatured olive o i l . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cottonseed o i l , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Raw linseed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
P e r cent 0.37 3.09
0.18
1.12
Since the object of the study was merely to compare test,ing methods and not to secure exact data on any oil in particular, no other chemical constants are presented. For the sake of brevity, the results of four oils only are shown in the accompanying curves. Discussion of Results
Results obtained by the original Mackey method seemed to divide the oils sharply into two classes. Since there is no such sharp division evidenced by practical experience, attempts were made to secure more informative results by
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modifying the method. The logical improvement in the Mackey method seemed to be along the lines of decreasing the heat loss from the sample, and the easiest way to do this was to secure better insulation by increasing the size of the sample itself. The curves in Figures 3 and 4 show the results obtained using 15-gram and 30-gram samples. The gauze cylinder used to support these larger samples was made of brass about 12 mesh, the dimensions being 2.5 inches diameter, 6 inches high. An examination of the curves will reveal results which are unusual and in some respects contrary to past ideas. It has always been thought that cottonseed oil was much more hazardous than lard oil. This is borne out by the results obtained from the original Mackey method (Figure 2). However, it will be noted in Figures 1 and 4 that a greater oxidation rate is evidenced by pure lard oil than by cottonseed oil. The test conditions as expressed in the Mackey using a 30-gram sample more closely approximate the conditions of the constant temperature difference method than do those of the original Mackey. Consequently, if the results shown in Figure 1 are correct, they should be substantiated at least in some degree by the results of Figure 4. This is the case because the heating curve of pure lard oil lies ahead of that of cottonseed and that of denatured olive oil as well. The only explanation we have to offer for this peculiar behavior is that the heating rate of pure lard oil, although initially greater at a definite temperature than that of cottonseed oil, is not subject to as great an increase due to the catalytic action of the products of its oxidation. Therefore, when tested by the original Mackey method, the rate of heat production from the oxidation is not sufficient to raise the sample temperature to ignition values. When a 30-gram sample is used, however, the heat loss from the sample is much less in proportion to the total heat available. Under these condi-
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tions the sample oiled with lard oil starts ahead of that oiled with cottonseed and the latter is not able to catch up to it in spite of the accelerating action of its oxidation products. Products of partial oxidation are really among the most active accelerators of spontaneous heating. These oxidation products vary, of course, as the composition of the original oils varies, so that their effect is more marked in some cases than in others. I n examining a curve resulting from a spontaneous heating test, one should look for the action of these accelerating agents. When testing by the Mackey method, temperatures favoring ignition will be obtained only when the original oxidation rate of the oil is sufficiently great to increase the temperature of the sample to a value of approximately 250" F. (139" C.) above its surroundings, or when the rate of oxidation reaches an equivalent value by acceleration due to oxidation products. Under the conditions of the method in which a constant temperature difference is maintained, it is only necessary that the oxidation rate of the sample be sufficient to keep the sample temperature more than 2" C. above its surroundings. As has been mentioned previously, similar conditions are found quite often in practice and have been the cause of fires which heretofore have had no satisfactory explanation. The new method will indicate heating tendencies almost from a start, even in the case of oils such as castor oil. I n fact, a t initial test temperatures approximating 250" F. (121' C.) there is evident heating from samples of cotton oiled with pure mineral oils only. Suggestions for Testing Laboratories
Any information regarding the hazard of an oil must in every case take into account the conditions under which it is to be used. Eyen castor oil will heat spontaneously to ignition temperatures under the proper conditions. Further-
March, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
more, there is not and cannot be any sharp distinction between hazardous and non-hazardous oils; variations in condition of use may entirely change the relative hazards of two or more of the common commercial oils. Extreme care is necessary in obtaining significant data regarding the action of certain vegetable and animal oils which are either diluted with mineral oils or to which agents have been added which tend to retard their oxidation. For example, a mixture of 50 per cent cottonseed oil and 50 per cent asphalt-base mineral oil becomes dangerous OIL continued exposure to temperatures slightly above normal. However, when the fresh mixture is tested by any method now available
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there is no evidence of this peculiar action unless the duration of the test is considerably more than 3 hours. Consequently, tests of tendency for spontaneous heating should be made in conjunction with a reasonably critical chemical examination. It is necessary to look out for the presence of retarding agents. These agents have nearly always an affinity for oxygen and are usually soluble in water as well as in the oil. Whenever chemical examination shows the presence of reducing agents or any appreciable proportion of mineral oil in the sample, the spontaneous heating test should be continued for a longer time than usual.
A Simple and Inexpensive Kjeldahl Digestion Apparatus1s2 By E. G. Hastings, E. B. Fred, and W. H. Peterson DEPARTMENT OF AGRICULTURAL BACTERIOLOGY A N D AGRICULTURAL CHEMISTRY, UNIVERSITY OF WISCONSIN, MADISON, WIS
A
LTHOUGH many types of Kjeldahl apparatus have been described,3 the writers have seen none so effective and cheap as the one described herein. The total cost of the apparatus for twelve flasks without the gas burners and rack is about fifty dollars. KO hood or suction fan is required. For two and one-half years this apparatus has been in constant use in our laboratory; during this time more than five thousand analyses have been made and it has always proved most satisfactory. The apparatus is shown in detail in Figure 1 arid in operation in Figure 2. It consists of a large lead tube 26 mm. (11/4 inches) internal diameter, with lead side arm tubes 9 mm. ("8 inch) internal diameter, and 15 cm (G inches) long carrying movable lead stoppers. These lead stoppers should be so constructed as to move freely up aiid down the
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Figure 2-One Figure 1-Cross Section of Water Injector and One Branch of Kjeldahl Digestion Apparatus
side arm tubes and thus accommodate Kjeldahl flasks with varying sizes of necks. The digestion tube is connected by a coupling t o a water injector. This consist,s of a small lead pipe passing into the larger fume tube. The end of this small pipe is closed except for the small holes as shown Received October 30, 1926, Published with the approval of the Director, Wisconsin Agricultural Experiment Station. 8 For example, S y , THIS JOURNAL, 4, 680 (1912). 1
in the figure. When the water is turned on it escapes through these holes and passes down through the fume tube, creating a suction. The flasks are joined as shown in Figure 2 and before the gas burners are lighted the water is turned on to give a slight suction. Air is thus drawn into the flasks around the loosely fitting lead stoppers and into the side arms. This current of air carries the gases produced from the flasks through the small and the large lead pipes and brings them into contact with water, which absorbs them and carries them into the drains. The writers' apparatus is designed for long-necked Kjeldah1 flasks. If short-necked flasks are used, it is necessary to change the distance of the digestion rack from the suction tubes. To secure the best results a flask should be connected to each side arm or the openings of the unused side arms closed with lead stoppers. Once digestion is well under way it is not necessary to seal all the openings. Apart from simplicity in construction and ease of manipulation this Kjeldahl digestion apparatus has other advan-
Unit of
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Apparatus i n
tages. It works so well that it can be installed in a genera1 laboratory, thus making it possible, to watch the progress of the digestion while other work is being done. The time of digestion is somewhat less than that required for the usual hood method. The apparatus is economical in its use of acid. Since the entire apparatus is exposed, the necks of the flasks are cooler than those under a hood and thus not so difficult to handle. The apparatus was designed and made by W.G. Huebner and M. F. Robinson of the University of Wisconsin Service Department.
