ANALYTICAL CHEMISTRY
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A.S.T.M. method D721-47; the precision appears to be equally Paraffin satisfactory. The semimicroA.S.T.M. Method D721-47 Socony-Vacuum Semimicromethod Wax method may be applied t o Sample Operator A Operator B Operator C Operator D microcrystalline wax with simi0.11 0.12 0.08 0.11 0 . 0 6 0 . 1 0 0.14 0.16 0.05 1 0 . 1 1 0.10 0.16 0.47 0.52 0.56 0 . 5 5 0.51 0.52 2 0 . 4 8 0.4b 0 . 4 5 0.53 0.49 0.55 lar success. 1.02 1.27 1.29 1.08 1.15 0.99 1.23 1.03 3 1.02 1.05 1.26 1.26 2.6 2.6 2.7 2.9 2.7 2.6 2.9 2.7 2.7 4 2.6 2.8 2.6 The equipment required for 7.1 6.8 7.2 7.5 7.5 7.3 7.0 7.0 7.9 5 7.8 7.4 6.9 the test is simple, inexpensive, 8.2 8.1 8.7 7.8 8.0 8.6 8.8 8.4 8.3 6 8.4 9.1 8.3 and can be readily constructed Microorystalline in a laboratory. The apparatus Wax and technique permit appreciable Gample Socony-Vacuum Macromethod Socony-Vacuum Semimicromethod 1 3.9 4.4 4.4 ?,7 3.4 3.7 3.7 3.7 3.4 3.3 saving in solvents, bench space, 5.8 5.3 0.3 5.3 5.7 7.2 7.0 6.6 2 6.6 5.6 and cooling capacity when com7.4 7.8 7.4 7.4 7.6 7.7 8.0 7.4 3 7.8 7.5 7.7 7.4 10.9 11.1 11.9 11.2 11.2 13.4 13.1 11.1 4 12.6 10.4 10.7 10.4 pared with method D721-47. The method is excellently Table 11. Average Values and Deviations in Test Results adapted for control operations in refinery laboratories. Average Results Average Deviations Paraffin A.S.T.M. S.-y. A.S.T.M. S.-V,. The most significant advantage of the method is its time-saving method se,misemiCombined Wax method feature. After adequate practice, a nontechnical operator should D721-47 micro micro average Sample D721-47 be able to complete a determination in approximately 1 hour. At 0.02 0.03 0.10 0.11 1 0.11 0.04 0.04 0.52 0.51 2 0.49 least 6 hours are generally required for a similar result by method 0.10 0.10 3 1.16 1.11 1.14 4 2.68 2.72 2.70 0.08 0.08 D721-47. The method has the speed of less reliable routine pro0.32 0.26 6 7.15 7.42 7.28 cedures, but appears to have the precision required for a referee 0.30 0.25 8.58 8.39 6 8.20 method. hlicrocrystalTable I.
Comparative Oil Content Data on Paraffin and Microscrystalline Waxes
E:!
line Wax Sample 1 2 3 4
S.-V. macro 3.92 6.34 7.62 12.2
z:;
s.-v.
3.45 5.48 7.57 10.8
3.68 5.91 7.59 11.5
macro 0.32 0.83 0.22 1 .o
ACKNOWLEDGMENTS 0.25 0.42 0.13 0.7
Table I1 shows the average results and the deviations therefrom. It will be seen from these data that, with respect to paraffin waxes, the semimicrotechnique is as reliable as method D721-47, and in the instance of the microcrystalline waxes, the method is as precise as the macrotechnique.
The preliminary suggestions as to procedure and apparatus were made by A. A. Benedetti-Pichler, Socony-Vacuum Laboratories consultant, whom the authors wish to thank for valuable advice. The authors also wish to acknowledge the cooperation of D. W. Robertson of their laboratory. LITERATURE CITED (1) Am. SOC. Testing Materials, Standards on Petroleum Products and Lubricants, Method D721-47, A.S.T.M. Committee D-2,
Philadelphia, Pa.
CONCLUSIONS
(2) Lee, R., and Kalichevsky, V. A., IND.ENG.CHEM.,ANAL.ED., 14, 767 (1942).
Oil content determinations by the Socony-Vacuum semimicromethod on paraffin waxes agree closely with results obtained by
RECEIVEDMarch 26, 1948. Presented before the Division of Petroleum SOCIETY, Chemistry a t the 113th Meeting of the AMERICANCHEMICAL Chicago, Ill.
Microscopical Distinction of Corundum among Its Natural and Artificial Associates Employing the Christiansen Eflect by Transmitted, Dark-Field Illumination GERMAIN C. CROSSMON, Bausch & Lomb Optical Co., Rochester,
C
ORUNDURI, a natural aluminum oxide with a Mohs' scale hardness of 9, is widely used in the grinding of lenses from optical glass. It is found in many parts of the world, but the Transvaal region of South Africa is the source of much of the material imported for use in grinding glass. In processing for use as an industrial abrasive, the imported material is crushed and screened. The grinding wheel industry makes use of the larger screen sizes and the optical industry the smaller sizes for the rough grinding of ophthalmic glass. The subsieve sizes required for grinding precision surfaces are prepared from the material recovered from the rough grinding operation by repeated free settling classification. The cake formed when the water has evaporated is cut by experienced workmen into portions having different average particle sizes. A control of the purity of the corundum is important at two different points. The sieve size material (60 t o 220 grit) pur-
N. Y .
chased for rough grinding is checked with the microscope to see that the amount of quartz, mica, magnetite, etc., is not excessive. The subsieve size fine grinding powders recovered from the rough grinding operations are examined for the above impurities and also for the amount of glass that remains mixed with the corundum. Too much glass will decrease the grinding speed but approximately 15% glass will act as a source of slowly released alkali silicate that will serve as a dispersing agent to prevent agglomeration of the fine corundum into lumps during classification and use. METHOD
The microscopical inspection of corundum can be made by employment of the Christiansen effect (1, $, 3) by one not trained or equipped for petrographic work. Any microscope having an Abbe condenser of 1.25 N.A. and an achromatic 1OX objective
V O L U M E 20, NO. 10, O C T O B E R 1 9 4 8
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The Christiansen effect is employed to distinguish particles of corundum among its associates in abrasive emery powder either i n its natural state or after i t has been used to polish glass. This method is especially helpful i n the quantitative microscopical estimation of corundum before and after abrasive use, because easy rapid recognition of the corundum among all its associates is obtained with an ordinary compound microscope, without need for petrographic accessories. The method may be extended to any system of phases in which the liquid medium is of favorable refractive index and dispersion, and the relevant determinative properties of significant phases differ sufficiently from one another.
of 0.25 S.X.can be used.
The microscope lamp must be very bright, such as a 6-volt 108-watt ribbon filament bulb, and should be equipped with a blue and ground-glass or Daylite filter. The upper element of the Abbe condenser is removed and a dark-field stop approximately 16 or 17 mni. in diameter is placed in the carrier below the condenser. The abrasive grains are distributed evenly on a glass slide, a drop of methylene iodide is added, and the slide is covered with a thin cover glass. The methylene iodide should be of a refractive index of approximately nD 1.74 at 25’ C. t o function satisfactorily with corundum with an “average” refractive index of about 1.77. I t is important that t,he slide and cover glass be clean and free from scratches. The microscope is focused on the preparation and the plane substage mirror is adjusted so that the field is evenly illuminated. The condenser is then racked up or down as may be necessary to make the abrasive grains appear bright against) a dark background .
solid are placed in a liquid having the same refractive index as the solid for one wave length of light but a different refractive index for other w-ave lengths, the color for which the refractive index of the liquid and solid match will be transmitted without deviation but other wave lengths will be deviated. When a microscope is adjusted for dark-field illumination, only the deviated colors reach the eye. The method of inspection described gives less information than would result from skilled petrographic or mineralogical microscope study. It is preferable for obtaining approximately quantitative information about a qualitatively familiar system because it saves time, skill, and equipment.
RESULTS
(1) Chamot. E. M.,and Mason, C. W., “Handbook of Chemical Microscopy,” Vol. I, New York, John Wiley & Sons, 1938. (2) Crossmon, G. C., J . Optical SOC.A n . , 38,417 (1948). (3) Dodge, N.B.,Am. Mineral., in press.
Corundum particles (grain size 500 to 1600), whether natural or synthetic, as seen by this met,hod are golden yellow or yellow with purple or blue borders. Silica, mica, and most types of glass appear white. Mica can be identified as thin flakes showing evidence of basal cleavage, and any iron or magnetite that may be present will be dark and opaque. .4sample may be rejected if the proportion of corundum grains is lower than that found in a chemically analyzed sample selected a.5 a standard. DISCUSSION
The basic method can be used for easy identification of any constituent of a mixture of transparent particles if the other materials in the mixture differ substantially in refractive index, “opacity,” color, size, shape, or other convenient property. The immersion liquid must be selected so as to have a refractive index near that of the material to be observed and a much higher dispersion. For an index range of from 1.440 to 1.628, mixtures of diethylene glycol monobutyl ether and Halowax oil (technical grade of a-chloronaphthalene) are suggested. Mixtures of Halowax oil and a-bromonaphthalene can be used for the range between 1.632 and 1.656 and a-bromonaphthalene and methylene iodide from 1.660 to 1.70. Mixtures of diethylene glycol monobutyl ether with cinnamaldehyde giving a range in index from approximately 1.440 to 1.62 are superior to the above for production of strong colors in mounted preparations. Increased magnification can be attained by the use of higher powered eyepieces with the 1OX objective or the use of the achromatic 43X objective of 0.65 K.A. If the latter is used, its numerical aperture must be reduced by the insertion of a funnel stop screwed into the objective far enough so as just to touch the back lens. h funnel stop with over-all length of 2.72 em. (1.092 inches) and aberture of 2.9 mm. (0.116 inch) has proved satisfactory for most preparations. The size of the dark-field stop located in the carrier below the condenser for use with this objective is approximately 22 mm. in diameter. Dispersion coloration results from the operation of the same principles of transmittance and refraction of light that govern the -action of the Christiansen filter (1). If particles of a transparent
LITERATURE CITED
RECEIVED February 28, 1948.
Standard Samples The National Bureau of Standards, Washington 25, D. C., has added six new materials to its list of analyzed standard samples. Standard Silicon-Aluminum alloy, No. 87, has the following percentage composition: silicon 6.22, nickel 0.59, iron 0.46, magnesium 0.39, copper 0.30 manganese 0.30, chromium 0.17, titanium 0.16, zinc 0.075, lead 0.070, tin 0.061. Price. $3.00 oer 65-gram unit. Standard Copper-Nickel Alloy (Monel type), No. 162, has the following percentage composition: nickel 66.38, copper 28.38, manganese 2.34, silicon 0.67, cobalt 0.54, iron 0.34, chromium 0.24, aluminum 0.23, titanium 0.20, carbon 0.11, sulfur 0.002. Price, $3.00 per 150-gram unit. Standard Cr-Xi-Mo Casting Steel, No. 160, is certified for the following constituents: carbon 0.044, manganese 0.68, phosphorus 0.012, sulfur 0.011, silicon 1.13, copper 0.053, nickel 8.90, chromium 19.13, vanadium 0.038, molybdenum 2.95. Price, 13.00 per 150-gram unit. Standard Nickel-Chromium Casting Steel, No. 161, is certified for the following constituents: carbon 0.34, manganese 1.29, phosphorus 0.012, sulfur 0.005, silicon 1.56, copper 0.04, nickel 64.3, chromium 16.9, vanadium 0.03, molybdenum 0.005, cobalt 0.47, iron 15.0. Price, $3.00 per 150-gram unit. Standard Low Carbon, 19 Cr-9 Ni Steel, No. 166, is certified for carbon only, 0.028%. Price, $2.00 per 100-gram unit. Standard Glass Sand, S o . 165, is certified for total iron, as Fe203= 0.0189. Price, $2.00 per 65-gram upit. The bureau now issues more than 400 kinds of standard samples of steels, irons, ferroalloys, nonferrous alloys, ores, ceramic materials, high-purity chemicals for standardizations, hydrocarbons, paint pigments for color, oils for viscometer calibrations, melting-point standards, and other reference standards. A complete list of the standards, fees, and other information is given in the supplement to Circular C398.
