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The data presented in Tables I1 and I11 show that the error is usually about 10 per cent but occasionally amounts to 20 per cent. It may be possible to reduce the error by using a photoelectric comparator for evaluating the relative intensities of the lines; the authors have not tried this.
to interfere in any way with the spectrographic determination. Moreover, the single sulfide precipitation and the single spectrogram would suffice for the determination of many of these other elements, provided that the calibration curve had been constructed for each of them.
Limits of the Method The upper limit of this method is probably somewhat higher than 0.2 mg. of zinc; the authors made no attempt to ascertain the upper limit, since it is unlikely that amounts larger than 0.2 mg. of zinc would be encountered in 2 grams of plant tissue. If such were the case, one could use a smaller sample. The lower limit of the method, with the concave grating, is about 0.005 mg. of zinc, which on a 4-gram sample amounts to about 1 part per million. With a quartz prism spectrograph, both the upper and lower limits may be considerably lower.
Summary A quantitative spectrographic method for the determination of zinc in plant material has been studied and presented. The range of the method is from about 1 to 100 p. p. m., or more, depending on the size of the sample used. Cadmium is used as the internal standard, the zinc and cadmium being co-precipitated as the sulfides before arcking. No other elements are present in the sulfide precipitate in amounts sufficient to cause interference. The maximum deviation from the mean of duplicate analysis is about one part in five.
Interference This proposed method of precipitating the zinc as the sulfide along with the reference element, cadmium, also includes in the precipitate all the other elements whose sulfides are insoluble in a weakly acid solution. However, none of these other elements occur in plant tissue in amounts sufficient
(1) Fales, H.A,, and Ware, G. M., J. Am. Chem. SOC.,41,478 (1919). (2) Hasler, M.F., and Lindhurst, R. W., Rev. Sci. Instrumente, 7, 137 (1936). (3) Rogers, L.H.,IND.ENG.CHEM.,Anal. Ed., 7,421 (1935). (4) Scheibe, G.,and Neuhkusser, A., Z. angew. Chem.,41,1218 (1928).
Literature Cited
RECEIVEDMay 4, 1936. Paper No. 355, University of California Citrus Experiment Station and Graduate School of Tropical Agriculture.
Photometric Determination of Iron in Used Engine Oils A. R. RESCORLA, E. M. FRY, AND F. L. CARNAHAN, Petroleum Refining Laboratory, The Pennsylvania State College, State College, Pa.
The iron content in the ash of oils subjected to service tests may be readily determined by means of a photometric colorimeter. Even small amounts of wear may be followed closely without interfering with the continuous operation of the motor.
S
MALL amounts of iron are frequently determined
through the formation of ferric sulfocyanide, visual matching with the color produced in a sample containing a known amount of iron being utilized. The proposed method involves measurement of the intensity of color produced by means of light from a fixed source passing through a thin layer of solution in which ferric sulfocyanide has been formed, and impinging upon a photronic cell. This has been applied especially to the determination of iron in used crankcase oils. It is well known that internal-combustion engine wear may be estimated from the iron content of the crankcase oil (1, 3, 4, 6). Such a means of attack on this important problem carries with it several advantages over wear determination by micrometer measurement or by change in weight of certain parts during a run. It is not necessarily true that d parts of the engine are abraded to the same extent as those measured or weighed. A long engine test with its attending expense and inconvenience is needed to obtain the desired accuracy of measurement; under these circumstances conditions in the motor may vary to such an extent that a fair comparison of two oils in successive runs may not be secured. The lubricating oil, however, reaches all parts of the motor
subject t o wear-it is reasonable to suppose that its total iron content is an index of the abrasion which has occurred, Very small amounts of wear, undetectable by physical measurement, may be estimated. About 10,000 miles of engine operation are required to cause cylinder wear of 0.0025 om. (0.001 inch), while the wear in 10 miles may readily be detected by this chemical method. Furthermore, the progress of wear may be followed without even stopping the engine. The method permits one man to make six iron determinations in duplicate in 8 hours, and is applicable to the determination of iron in amounts from 0.00005 to 0.0015 gram. Duplicate runs on each of 321 used oils showed an average difference of 3.8 per cent. It is considered that this difference is due largely to difficulty in sampling, as the average difference encountered with calibration samples containing known W
FIGURE1. PHOTOMETRIC COLORIMETER A. Direct current microammeter B. Weeton photronic cell, Model 694 C. alas8 cell for solution D . Screw arrangement for moving cells
E. Light source (100-watt 115-volt Mazda R. Alternating current voltmeter a. Voltage control rheostat H. Alternating current souroe I. Meter stiok J . Indicator pointer
JULY 15, 1936
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243
is obvious that calibration may be effected by using samples of known iron content and noting the distance of a mark on the movable carriage from the light source. It was thus not necessary to have constantly on hand standard solutions for comparison. Color matching by visual inspection may introduce large personal error or may even be impossible for some operators. The current from the photronic cell, however, was read on a microammeter and could be adjusted to the desired value very readily. A glass cell, 50 X 60 X STANDARDIZATION OF PHOTOMETER. 10 mm., filled with distilled water was placed in a holder directly
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a2
04
Ob
08
IO
I2
14
16
I8
90
22
W E t W OF IRO4 MILLIGRAMS
FIGURE 2. CALIBRATION CURVEOF PHOTOMETER FOR IRON ANALYSIS
amounts of iron was 0.4 per cent. Runs on oils to which ferric oleate had been added gave an average result 0.2 per cent higher than the theoretical amount, the greatest deviation for any one of the four samples being 3.58 per cent. These data are shown in Table I. The colorimetric analysis of the oleate itself is indicated in Table 11. TABLBI. ANALYSESOF OILS CONTAINING FERRIC OLEATE Iron Present % 0.000446 0.000446 0.000446 0.000446 Av. 0.000446
Iron
Found % 0.000455 0.000462 0.000436 0,000436 0.000447
Difference
% +2.02
+3.68 -2.24 -2.24 +0.2
TABLE11. COLORIMETRIC ANALYSISOF FERRIC OLEATE Sample Gram 0.0990 0.0990 0.0333
Iron Present %
Iron Found %
6.21 6.21 6.21
6.3 6.2 6.0
in front of the photronic cell. With an indicator on the movable platform 100 cm. from the light source, the intensity of the latter was adjusted by varying the current until a microammeter showed the photronic cell to be delivering 19 microamperes. This value was arbitrarily chosen as a convenient one for use. The standardization of the colorimeter was effected by the use of solutions of ferric iron. Solutions containing up to 0.0022 gram of ferric iron were prepared by well-known procedures from ferrous ammonium sulfate and ferric sulfate which had been analyzed gravimetrically for iron content. To 90 cc. of solution containing the desired amount of iron 10 cc. of N ammonium sulfocyanide were added (this is equivalent to at least twenty-five times the maximum amount, 0.0015 gram, of iron present). The mixture was placed in the glass cell directly in front of the photronic cell, and with the light source maintained at the voltage determined by the use of distilled water at 100 cm., the position of the assembly was varied until the current from the photronic cell became 19 microamperes. The calibration curve as shown in Figure 2 was obtained in this wa . It was found that the iron present in reagents (iron-free $drochloric acid and ammonium thiocyanate) was so small that no correction was required. PROCEDURE. A IO-gram representative sample of the oil was very carefully ashed in a quartz crucible. No fusion of the ash with the quartz crucible was noted; however,, platinum may be used if desired. To the ash in the cooled crumble were added 20 cc. of iron-free, concentrated hydrochloric acid with gentle heating to dissolve any oxide sticking on the walls. The mixture was then washed into a beaker and boiled for 10 minutes. The liquor was transferred to a 100-cc. graduated cylinder and diluted t o 90 cc. Next 10 cc. of normal ammonium sulfocyanide were added with thorough mixing. A portion of the mixed solution was put in the glass cell, the voltage of the light source was adjusted to the value used in calibration, and the position of the carriage holding the glass cell and photronic cell fixed t o give a current of 19 microamperes. The amount of iron in the sample was then found from the calibration curve. Should there be any turbidity or evidence of suspended material in the colored solution, it must be filtered before being introduced into the containing cell.
Discussion of Results In the determination of iron by the sulfocyanide method, silver, mercuric chloride (6),cobalt (8),and bismuth @)should be absent. It is stated that tests are best carried out in the absence of phosphates, borates, oxalates, acetates, tartrates, and citrates (7). Oxalic and phosphorous acids interfere (10); the color produced by nitric acid is destroyed on boiling, though it might be mistaken for that of iron in the cold. Alkaline earth chlorides are detrimental (8). Organic matter, certain mineral acids, and many metals do not cause any difficulty.
This method has been found to be suitable for the estimation of iron in amounts ranging from 0.00005 to 0.0015 gram, Aliquot portions of solutions containing large amounts of iron may be taken for analysis. With amounts of iron in the cell greater than about 0.0015 gram, the reproducibility of the method does not justify its use. The results shown in Figure 3 may be taken as illustrative
Experimental The procedure consists in general of ashing the oil, dissolving the residue in hydrochloric acid, adding ammonium sulfocyanide solution, and estimating the amount of iron present from the intensity of light projected by a fixed source through a thin layer of solution upon a photronic cell. The instrument, shown in Figure 1, in which color comparison W.BS made was a colorimeter similar to that of Story and Kalichevsky (9),and consisted essentially of a fixed light source and a movable photronic cell with a container between them for the sample. The last two items were mounted on a movable carriage which was so placed in operation as to produce a certain specified current from the photronic cell. It
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9
4
5
6
7
8
HOURS OF OPERATION AT 6 0 MILES PEE HOUB
FIGGRE 3. WEARIN Two DODGE ENGINES LUBRICATED WITH THE SAME OIL
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of the increase in iron content of an oil in engine service. KO correction has been made for the oil consumed during the run. The same oil and operating conditions were used, but different engines were involved in the two cases shown. The rapid increase in iron content a t the beginning of a run is of interest. I t has long been known that intermittent service causes greater engine wear than continuous running. The colorimetric method of analysis for iron is a convenient means of confirming this circumstance and affords an indication of rates of wear under various conditions.
Acknowledgment This work was a part of the research program of the Pennsylvania Grade Crude Oil Association and is published with its permission and that of the School of Chemistry and Physics of The Pennsylvania State College.
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Literature Cited (1) Boerlage, G; D., and Gravesteyn, B. J . J., Motorship (British), p. 171 (A4ugust, 1932). (2) Heinrichs, H., and Hertrich, M., Glastech. Ber., 2, 112 (1924); Chimie & industrie, 14, 696 (1925). (3) Keller, George H., Automotive Ind., 72, 484 (1935). (4) Langdon, Howard H., State Coll. Wash., Monthly Bull. 15, No. 2 (July, 1932); Eng. Expt. Sta., Eng. Bull. No. 41. (5) Merrill, D. R., Moore, C. C., and Bray, U. B., Oil Gas J.,34, No. 4, 59 (1935); No. 5 , 55. (6) Partington, “Textbook of Inorganic Chemistry,” 4th ed., p. 979, London, Macmillan Co., 1933. (7) Prescott and Johnson, “Qualitative Chemical Analysis,” p. 320, New York, D. Van Nostrand Co., 1933. (8) Scott, “Standard Methods of Chemical Analysis,” 4th ed., Vol. 1, pp. 261-2, New York, D. Van Nostrand Co., 1925. Story, B. W., and Kalichevsky, V. A., IND. ENG.CHEM.,AnaI. Ed., 5, 214 (1933). (10) . , Walker, W., Analyst, 50, 279 (1925).
RECEIVED March 23, 1936.
Identification of Crvstalline Materials J
Classification and Use of X-Ray Diffraction Patterns J. D. H.4N.4WALT AND H. W. RINN, The Dow Chemical Company, Midland, Mich.
I
S THE course of the pa- t
the origin of the unknown few years, x-ray aud lines in the s p e c t r a obtained. spectroscopic methods of Similarly, in the w a y analpis have found an infield, o n e of t h e t h i n g s creasing usefulnesi at the Dow Chemical Company. which will greatly facilitate There are a large number the use of x-ray ponder of different tvuez of urobuatterns in identifwna un.~ DIFFRACTION PATTERNS IN CALIknowns is to have ivazable FIGURE1. X-RAY POWDER lems on which information BRATED SCALE a reference library of standcan be o b t a i n e d by the variations of a p p a r a t u s ILloK, radiation ard patterns of known substances. However, because a n d technic which are there are thousands of common chemical substances, the job of possible in these two fields. It is not the purpose of this taking the standard patterns, and more especially of finding paper, however, to discuss these methods or applications in an adequate system of indexing or classifying thousands of difgeneral, but to describe in some detail a scheme of classifying fraction patterns, is considerable and in general has not been and using x-ray diffraction patterns which has been found thought feasible (6). It has been found in this laboratory that very helpful in one particular application of x-rays-namely, the problem of classification of the patterns presents no practhat of identifying unknown substances by means of their tical difficulties and that in so far as they can be obtained, Hull powder diffraction patterns. they can be effectively used in the identification of unknowns. The inherent power of x-ray diffraction as a practical The real limitations to the field of applicability of the x-ray means of chemical analysis was pointed out a good many method are due to more fundamental factors, such as lack years ago (2, 4). Having a different theoretical basis and of sensitivity to small percentages of the minor constituent depending upon an entirely different technic than other methand to the small effects sometimes encountered in changes of ods, it would be expected to suppIement the information to solid solution concentration and lack of sensitivity because of be obtained from other methods and, a t times, to be applicable the poor crystalline structure of some materials. A recent where other methods are not suitable. It appears, however, article by Waldo (5) gives the results of a similar attempt a t that the use of this method has not increased a t a rate comclassification applied to about 50 copper-ore minerals. A mensurate with its unique and valuable features, and that it comparison of the classifications will be made in connection is used by relatively few academic and industrial laboratories. with the detailed description of the present method. Probably one of the main reasons for this is that x-ray Identification of complete unknowns does not form the diffraction is not a practical, economical method of analysis bulk of the work or the most important part of the applicaas long as it involves any time-consuming process such as tion of x-ray diffraction patterns. However, as the stock of the determination of crystal structure. For the purpose of patterns obtained in the course of the authors’ use of x-ray analysis, however, there is no advantage in knowing the diffraction continued to enlarge, the advantage of having an crystal structure, since any substance is just as uniquely index to them became apparent. The system of classification characterized by its diffraction pattern. For practical usage, which was finally adopted has been in operation since June, the x-ray diffraction method must be put upon an empirical 1934, and, though the number of patterns has greatly inbasis, as has been done, for example, in spectroscopic analysis. creased since that time, has proved to be fully adequate to There are available for the spectroscopist portfolios of the handle them. The authors now have over 4000 patterns, of arc and spark spectra of the elements, and also convenient which 1054 are individual inorganic chemical substances. tables of wave lengths which serve to assist him in identifying “ 1
