October 15, 1931
347
INDUSTRIAL A N D ENGINEERING CHEMISTRY
The advantages of this apparatus over that of Pregl are several. This one can be used for any method in which he uses the glass filter (3, p. 136) as in halogen and phosphate determinations. It can also be used in place of the microNeubauer crucible in the determination of sulfate. An accuracy as great as Pregl reports for sulfate determinations is not claimed for this method, for his method of ignition and rewashing is not easily adapted to this apparatus. However, i t is felt that an accuracy of *0.1 per cent is rarely necessary on such small samples as are here used, and the saving in time and labor is very considerable over his method. I n the determination of sulfur by combustion as described by Pregl (3, p. 152), difficulty due to a large volume might be encountered. Since it is only necessary to weight the filter tube B, it is possible to make the reaction chamber A as large as desired so that this difficulty is readily overcome. No loss of precipitated barium sulfate through the filter is necessary if it is properly coagulated by heating and the asbestos pad is made from fine enough fiber. This apparatus is decidedly less costly than the micro-Neubauer crucibles and much more simply
Determination
Of
manipulated. A much smaller amount of glass is weighed than with Pregl's glass filter tubes, and here again the manipulation is simpler, Likewise, the speed of filtration is decidedly greater, since there are several holes in the platinum disk, each one of about the same diameter as the single hole in the glass filter tube. The amount of asbestos is also smaller. Many other uses in gravimetric analysis may suggest themselves. It should, for example, be entirely feasible to carry out gravimetric calcium analyses by this procedure, if the suggestion of Willard and Boldyreff (4) of igniting the oxalate to carbonate at 460' C. is followed. In biological work, it is frequently desirable to use gravimetric methods for small amounts of organic materials, and here the determination might be simplified by use of this apparatus. Literature Cited (1) Barber, H H I and Kolthoff, I. M., J A m Chem. Soc , 60, 1626 (1928) (2) Kirk, P L , and Schmidt, C.L. A , J . Bzol. Chem , 83, 311 (1929). (3) Pregl, F., "Quantitative Organische Mikroanalyse," 3rd ed , Springer , 1930 (4) Willard, H H I and Boldyreff, A W , J Am Chem. Soc , 6 2 , 1 8 8 8 (1920)
Smoking Point
Fats'
John M. McCoy MEATINSPEC~ION LABORATORY, BUREAUOF ANIMAL INDUSTRY, WASHINGTON, D C.
HE smoking point of a fat is the lowest temperature at
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which sufficient decomposition takes place to produce visible smoke. As is well known, all fats decompose when heated to sufficiently high temperatures, with the formation of a variety of volatile substances, the most characteristic and familiar of which is acrolein. When observed under appropriate conditions, these volatile decomposition products appear as visible smoke. The significance of the smoking point has been recognized for some time. Blunt and Feeney (1) studied the factors affecting the smoking point, its bearing on the utilization of fats, and described a method for its determination. Although this method is suitable for the comparison of different fats, at the same time it does not take into account all of the factors which may cause variation in the smoking point observed, and on that account is not satisfactory for use by various observers working in different l a b o r a t o r i e s and at different times. A more exactly standardized method is therefore required. I n the work of this laboratory, it has been found desirable to determine the smoking point on a number of samples of fats submitted for examination. As soon as the work was undertaken, the need of a standard method became evident. Accordingly, the method described was developed. The apparatus used, pictured in Figure 1, is simple, the time required for making determinations is short, and the degree of accuracy is sufficient for the purpose. The method consists in heating the fat under uniform c o n d i t i o n s until smoke amears, and -noting the temperature. In preliminary experiments it was found that the smoking point is affected by the rate of heating and conditions of observation. Possibly the area of the surface exposed to air is also a factor. In order to attain uniform results, it is necessary, therefore, to heat a definite quantity of fat in a container of standard size
and dimensions and observe the smoke under standard conditions. Electric heaters of the type commonly used for Kjeldahl digestions (Gilmer heaters) were selected for heating. A rheostat is connected in series with the heaters so that the rate of heating can be reduced as the anticipated smoking point is approached Two heaters are connected in series with the rheostat. The top of one heater is covered with an asbestos plate with a 2'/4-inch (5.71-em.) circular opening in the center. the other bya similar plate with a 7/8-incli(2.22-em.) opening.
Figure 1-View
of Apparatus
I
1 Received
June 22,1931.
The containers used are standard 100-cc. round-bottom flasks, G om. in diameter with 6-em. neck, and made of Pyrex glass. To make the smoke more readily distinguishable, a black screen 11 X 14 inches (27.94 x 35.56 cm.) in size and made of dull black cardboard, such as is used to protect photographic paper from light, is placed directly behind the heaters.
ANALYTICAL EDITION
348
Natural light was found unsuitable on account of its variability. It was found necessary, therefore, to standardize the lighting. Accordingly, the apparatus is set up in a relatively dark place and dependence placed on artificial light. A lamp designed for microscope illumination, equipped with a 100watt bulb and daylight glass, is used for illumination. The daylight glass renders the smoke more readily visible than i t would be by uncorrected artificial light. The smoke point should, therefore, be observed by corrected artificial light. The apparatus must be set up in a place which is protected from drafts, as even a moderate current of air affects accuracy. Procedure Melt the fat, allow moisture and suspended matter to settle out, and filter. Pour 50 cc. of the melted fat into the flask, Set the flask on the heater which has the large opening in the cover plate. Suspend the thermometer from overhead so that the bulb is immersed in the fat, leaving the flask unstoppered. Heat the fat to between 110" and 115" C. Then remove the flask to the other heater, placing it in such a position that its open mouth is illuminated by a horizontal beam of light from the lamp and viewed against the black screen. The
Vol. 3, s o . 4
lamp should be placed as near the heater as practicable to secure maximum intensity of illumination. Adjust the rate of heating with the rheostat so that the temperature rises at the rate of approximately 2" C . per minute. Take the temperature at which the first wisp of smoke is seen rising from the top of the flask as the smoking point. The first wisp of smoke should be followed by a plainly visible and continuous stream, Remove the thermometer when smoke is first observed. Smoke should then be seen issuing from the mouth of the flask. If not, replace the thermometer and continue heating until smoke again appears and continues after the thermometer is removed. I n such case, the temperature at which the second appearance of smoke is noted is taken as the actual smoking point. The method described has been in use for more than a year and has given satisfactory results. After proficiency has been acquired, duplicate determinations made on separate portions of the same fat should agree within 1 or 2" C. Closer agreement might be attained by slowing the rate of heating in the final stage. Literature Cited (1) Blunt, K., and Feeney, C., J. Home Econ., 7, 535 (1915)
Solubility of Water in Aviation Gasolines'~' Elizabeth W. Aldrich BUREAUOF STANDARDS, WASHINGTON, D. C.
A method is described for the measurement of the concluded that all commercial solubility of water in liquid petroleum products, which gasolines are normally satuwhich collects in traps is applicable to the determination of traces of water in rated with water when used in and carburetors is of many organic liquids. Sodium-potassium alloy free internal-combustion engines. considerable interest to the from oxide is added to a weighed sample of the waterAlthough the solubility of operators of automobiles and saturated liquid after the removal of dissolved gases. water in gasolines is of interest airplanes. Even after preThe hydrogen evolved is collected and measured. Data in connection with a number cautions have been taken to are given on the solubility of water in five aviation gasoof problems, very little data remove all suspended water lines at three temperatures. on the subject could be found from gasolines, there remain in the literature. Apparently very ;mall amounts of dissolved water. A decrease in temperature will cause the sepa- none of the methods previously used for the measurement of ration of some of the dissolved water which, if collected in the the amount of water in solution in gasoline are above critifuel feed system over a sufficient period of time, may stop the cism. Accordingly, an investigation was made of the method flow of gasoline to the engine, The flow may also be inter- based on treatment of the gasoline with an alloy of sodium rupted by the accumulation of partially hydrated aluminum and potassium and determination of the volume of hydrogen oxide formed by prolonged contact of water with aluminum evolved. Data for a number of aviation gasolines were obfittings. In winter weather, water in the fuel feed system tained. may freeze and damage traps and carburetors. Choice of Method When water dissolves in a gasoline, the total vapor pressure of the gasoline increases by an amount dependent upon PREVIOUS METHODS-A number of methods (1) have been the degree of saturation. When saturated, the partial pres- described for the measurement of the water in petroleum sure of water va@r is not measurably different from the vapor products. Of these only two seen1 to be sufficiently precise pressure of pure water a t the existing temperature. This for the quantitative determination of the water dissolved in abnormally large increase in the vapor pressure caused by the gasolines. presence of small amounts of %ter indicates the necessity for The first of these was used by Groschuff (4),who measured complete removal of dissolved water or the saturation with the solubility of water in kerosene, benzene, and paraffin water at all temperatures when making accurate vapor-pres- oil. The temperatures were determined at which turbidity sure measurements on gasolines. Accordingly, the amount appeared and disappeared when known amounts of the of water required for the saturation of gasolines at various liquid and water were cooled and heated in sealed tubes temperatures is of interest. The results of the present study In this phase change method it is difficult to determine when indicate that the solubility at room temperature is about 1 all the water is dissolved, since the water tends to stick t o the part of water in 10,000 parts of gasoline, from which it may be side of the tube. It is also difficult to prevent undercooling. Presented before the Division of Petroleum 1 Received March 17, 1931. The second method is that developed by Clifford (3). Air Chemistry a t the 6 1 s t Meeting of the American Chemical Society, Indiandried over calcium chloride was bubbled through waterapolis, Ind , March 30 to Apill 3, 1931 saturated gasoline, and the air and vapors obtained were f Standards of Publication approved by The led through weighed calcium chloride tubes. Gasoline vapors S Department of Commerce
HE a m o u n t of water
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