Optical Society of America L. T. HALLEIT,Associate Editor
Traditional1 , dyestuff shipments have been tested by visual comparison o? yarns or fabrics dyed by standard procedures. The comparison is based on a standard dyestuff mutually accepted by the supplier and user. Because this method is both time-consuming and insensitive, many consumers and suppliers Some Techniques and Accessories to Facilitate the Application are turning to spectrophotometric measurements of the absorpof a G.E. Recording Spectrophotometer. E. E. RICHARDSON, tion of dye solutions for standardization and testing. The a p Iiodak Research Laboratories, Rochester, S. ’I-. plication makes use of the well-known Beer-Bouguer-Lambert law. Allowing for the infrequent occurrence of errors caused by a Fiducial marks for quickly placing the graph paper, a method lack of ability of the method to show differences in substanfor checking wave length, a system for cooling the light source, tivity of the dyestuff for the fiber, absorption spectrophotometry a convenient provision for replacing lamps, and an air-drying unit has been found of great value. attached to the amplifier are described. A modified integrating In the solution preparation, standard chemical analytical techsphere and its complete assembly having two hemicylindrical niques are used with the addition of certain precautions such a s tubes with a portion extending from the split lenses to the sphere control of pH, solution preparation temperature, time of standing, wall offer a means of making transmittance (total and specular) dye interaction effects, and concentration. All data and pertinent and reflectance (total and diffuse) measurements, and reduce information are placed on a card for each dyestuff. The strength stray-light errors in testing the transmittance of interference values expressed as per cent of standard concentration are entercd filters and fluorescent filters and solutions. Aluminum plates for on a control chart, the limits of which are chosen to indicate the supporting magnesium oxide surfaces, plates for the specular range of ac‘ceptablevariation in relation to the observed prtrcision ports, and specular light traps are described. A prism system of both the dyeing process and the variation of one shipment to has been constructed for testing small areas in the center of transanother. The standard deviation for five determinations of one parent objects 8 inches square and 5 inches in length and the axia.1 sampling is 0.33, expressed in per cent of standard, while that for area of lenses, especially photographic objectives. With this onc shipment to another is approximately 2.0. Correlation is obsystem reflectance can be measured a t 45O, with light polarized tained between this method and actual dyeing experience. It is in the plane of incidence. Accessories are used for measuring the of clear-cut value to an operating textile company consuming transmittance a t oblique angles for polarization both in and dyestuffs to use spectrophotometric solution measurcmvnts to perpendicular to the plane of incidence. A method for testing give not only an increased accuracy and precision over the test small areas without and with auxiliary lenses, a means of increzsdyeings, but also a saving of time of as much as 0.5 hour pi:r test ing the wave-length range from 425 to almost 1000 mp, and its on the average. wave-length calibration are explained.
S
papers were presented a t the meeting of the Optical Society of America in New York City, March 4,’5, and 6, which are of interest to analysts. They are abstracted below: EVERAL
Standards of Reflectance. HARRYJ. KEEGAN,Xational Bureau of Standards, Washington, D. C.
Applications of Spectrophotometry in a Textile Plant. I;I~B.:DT. SIMON,Shelton Looms, Sidney Blumenthal and Co., Inc.
ERICK
In 1931, the International Commission on Illumination adopted a resolution (3a) which may be translated as follows: “For the colorimetric measurement of opaque materials the luminance of the specimen studied ought to be expressed as a function of the luminance of a surface of the oxide of magnesium considered under the same conditions of illumination and observation.” Accordingly, the National Bureau of Standards further developed its technique for the preparation of magnesium oxide from freely burning magnesium turnings and published a letter circular (present number LC-547) describing the advantages and disadvantages of such a standard. Reference is made to this proceduie in three engineering test method sperifications : the spectral characteristics and color of objects and materials, a colorimetric test and pulp, and certain spectrophotometric and colorimetric test methods for paint, varnish, lac uer, and related materials. Although magnesium oxide standarls of reflectance are widely accepted in principle, it is understood that relatively few laboratories follow a technique of preparation that \Till yield the most accurately reproducible standards. T h i details of the technique developed a t the Sational Bureau of Standards are shown, together with calibrations of a working standard of reflectance made of machine-ground and polished white glass. These repeated calibrations made over a period of about 10 years show, from the minor random fluctuations, tl-e degree to which the successively prepared magnesium oxide standards are reproducible. The maximum spread in spectral reflectance is about 0.5yC.The calibrations also show from the lack of a significant regular trend in these fluctuations that the master working standards are permanent' to a degree even exceeding the best reproducibility that we have been able to obtain with magnesium oxide; and i t is far more permanent than magnesium oxide, which may yellow by a detectable amount within one day after preparat,ion. The bureau is noiv prepared to issue reflectanve standards of fire-polished white glass calibrated by comparison with the master standards. These standards of spectral reflectance are available both to public and private agencies for spectrophotometry and colorimetry.
Certain special methods of spectrophotometric technique have been developed or applied in connection with the problems cncountered in a textile mill. These mainly concein the measurement of dyed fabrics and the solutions of the dyes that are uscd to color them. Inasmuch as the methods of handling water-soluble dyes in aqueous solution are well known, only the procedurvb for preparing vat and naphthol dyes are discussed. 1Iulticomponcnt dye mixtures are the usual case encountered in dyeing and pi,inting of textiles. In order to obtain quantitative data 011 these mixtures, a polyethylene oxide condensate must be added to the solution to produce additivity. The concentration of each component of the mixture then can be accurately computed by mc:ins of a reciprocal matrix when a given combination is analyzed Icpeatedly. Some of the phenomena of the dyeing process are studied, using the spectrophotometer as a tool for the measurement of dye baths while the dyeing is proceeding. A miniature dye box was developed for simulation of production dyeing and is connected with a continuous flow cell placed in the spectrophotometer. These are discussed and demonstrated. Spectrophotometric Method for Determination of Lead. KENNETHH. SMITH,A N D S. F. BARR, GEORGEL. REYMANN, Stoner-Lludge, Inc. The application of a recording spectrophotometer as a useful tool in the development of techniques and methods of quantitative anabsis has been demonstrated. In the standardization of a procedure for rapid and precise determination of m i c r e quantities of lead in lacquers by the dithizone method, it was observed in measuring the absorption a t 520 millimicrons that a t low p H ranges high results and poor reproducibility were obtained. By a study of the transmission curves drawn by a G.E.Hardy recording spectrophotometer throughout the entire visual range, a second absorption band a t 620 millimicrons was observed. As the pH was raised the absorption a t 620 millimicrons decreased, reproducibility was improved, and values approaching the theoretical were obtained. An optimum pH range of 10.5 to 11 was thus quickly and easily established.
An Application of Spectrophotometry in the Textile Industry: A N D J. I.. Testing Dyestuff Shipments. E. P. MERSEREAU BARACH, -4lexander Smith and Sons Carpet Co.
387
388 Evaluation of the Elementary Causes of Deviations in SpectroGEFFSER,Keirton Steel Co. chemical Analysis. JOSEPH The difference betwen an individual spectrochemical determination and the ”true” composition of a sample may be divided into two parts: (1) a constant amount called the bias, equal to the difference between the “true” composition and the average of all such spectrochemical determinations made under essentially idrntical conditions, and ( 2 ) a variable amount called the deviation, equal to the difference between the individual determination and the average of all such determinations. The frequency distribution of the deviations of all determinations generally approximates the normal, and its sigma (standard deviation) is a measure of the uncertainty of the analytical method. The deviation of an individual determination may be subdivided further into components due t o elementary causes such as sample inhomogeneity, photographic response variations, excitation instability, and others. Using the statistical technique of analysis of variance, the contribution of each of several such elementar causes to the total uncertainty may be estimated, together wit1 fiducial limits within which the true value of each estimated contribution may reasonably be expected to lie. The results of a comprehensive experiment for evaluating the total uncertainty, the uncertainty components, and their fiducial limits for the spcctrochemiral analysis of copper in steel are reported. Quantitative Spectrographic Analysis of the Rare Earth Elements. \‘ELMER A. FASSEL A N D H. A. ~ ~ I L H E L MIowa , State College, Ames, Iowa. The spectrophotometric methods generally used for the quantitative analysis of the rare earths, do not permit the determination of low concentrations-i.e., less than 2% of rare earth impurities in another rare earth, and the determination of major amounts of those members of the group which possess no strong absorption bands in the wave-length region 2200 to 10,000 A. Emission spectra methods which are designed to supplement the spectrophotometric methods have been developed. The specific examples described are the determination of samarium in neodymium (0.1 to 2y0), europium in samarium (0.01 to 47,),and yltrium and gadolinium in complex mixtures (10 to 1000%). The methods, however, should be readily adaptable to similar detiTi,minations involving the other members of the series. Fcir the determination of minor constituents, the procedures involve the high amperage direct current arc excitation of rare earth oxide-pondered graphite mixtures. Selected lines of the major rare earth constituent serve as almost ideal internal standards. For the determination of major constituents in complex mixtures, similar excitation conditions are used. The selection of cerium as the internal standard for these dcterminations was based on the rrlative case with which any cerium present in a mixture could be preferentially separated from thc mixture and tlicn reintroduced in a standard amount. Studies on the, variation of the intensity ratios during excitations and the effect of large changes ,in arc current, pcr cent graphite, and rl-eiglit of sample charge on the integrated intensity ratios arc included. Precision and accuracy data indicate that the expcrimental error for duplicate determinations is about +4c; of the amount present. Wide Range Analysis for Zinc Using Spectrographic Line Widths. E. JOHXEASTXOSD A S D BERNICE E. \yILLIAhIS, t-.s. Department of Agriculture, Albany, Calif.
A spectrographic method has been developed for determination of zinc in biological ashes by use of line width as a concentration index. Synthetic standards and analytical samples, in the form of sulfates, are mixed 1% ith a potassium sulfate-graphite buffer containing barium and cadmium as internal rontrols. Samples are excited in a direct current arc and spectra recorded with a Littrow quartz spectrograph. The contour of Zn 2138 A. is recorded with a recording microphotometer and the width d,etermined a t the maximum density of the control l i n e m a 2255 A. or Cd 2288 A. A plot of the logarithm of this width us. logarithm of zinc concentration prepared from standard samples containing 0.004 t o lOy0 zinc serves as an analytical curve. Results determined by ordinary density measurements have been compared with those from width measurements. Although the two methods show comparable reproducibility of repeated exposures a t the lower limit of the analysis range, the width method is more precise a t higher ranges and has proved applicable even a t concentrations where the line density method is limited by self-reversal and low photographic plate contrast. Concentrations as high as
ANALYTICAL CHEMISTRY 10% have been determined, indicating possible application of such a method to the estimation of major constituents in such biological ashes or inorganic powders. Practical Applications of a Replica Grating Spectrograph Installation. J. T. Rozsa, National Spectrographic Laboratories, Inc. Techniques for analyses by a Wadsworth mounted replica grating spectrograph with mated accessories have been worked out on a variety of applications, including oil, low alloy steel, lead, aluminum, and zinc alloys, siliceous ceramic materials, blood, and general qualitative analysis. Working curves, analytical line pairs, exposure times, and general performance data are given. For applications not involving high spectral line count materials or extreme sensitivity quantitative work a replica grating will be found as satisfactory as an original grating. Image Contrast Control with Phase Microscopy. OSCARW. RICHARDS, American Optical Co. Four types of diffraction plates are possible, depending on whether the absorbing material is on ( A ) the conjugate, or ( B ) the complementary area, and the retarding medium is on the conjugate (+), or on the complementary area (-). Bright contrast occurs with A+ and B+ diffraction plates, because regions of longer optical path in the specimen appear brighter than those of lesser path; conversely, dark contrast occurs in the image when A - and B - plates are used. Dark contrast is useful when the image should resemble that from a stained preparation and for measurement. However, the dense contrast from A plates may obscure some of the underlying detail in the specimen, which would be visible with the more transparent dark contrast B - or bright cont’rast A+ diffraction plates. Bright contrast is useful for counting, motion study, and for stereophot,omicrographic analysis. Smaller objects are seen more easily in the image with bright than with dark contrast. Application of the Weber-Fechner law and the periodic principle reduces the many possible combinations of diffraction plates to those needed in practical microscopy. The image of small biological particles, as virus and certain cancer cells, has best contrast n-ith 0.1X retardation. Rlany specimens show best with X/4, but other highly refractile materials like glass require greater retardations. At l& magnifications ( +loox) a retardation of X/3 is often better than X/4. Khile different retardations could be obtained with one plate and light of different wave length, the differential sensitivity of the eye t o different colors precludes generally satisfactory application. Absorbing material on the diffraction plate increases the contrast in the image of both unstained specimens containing optical path differences and of weakly absorbing, poorly pigmented specimens. Increased visibility is often possible by the use of a diffraction plate whicsh increases the contrast in the image from the principal object and decreases the image contrast of interfering material. Further increased contrast is attained by combining color contrast and phase contrast in the image of specimens with selective wavelength absorption. Photomicrographs illustrate these principles. The Multipupil in Phase Microscopy. American Optical Co.
HAROLD OSTERBERG,
In the convcntional phase microscope the diffraction plate is located a t or inside the microscope objective and a t the ’plane conjugate to the condenser diaphragm. Condenser diaphragm and diffraction plate act as entrance and exit pupils, respectively. Additional real images of the condenser diaphragm may be formed by means of auxiliary lens systems. These images are called multipupils. Diffraction plates may be placed a t one or all of these multipupils. The increase in the length of a bipupil system can be moderate and can afford ample space a t the second pupil for the more complex elements of variable phase systems. As expected, multipupil systems function as effective phase contrast systems. It is shown on general theoretical grounds that the multipupil system is equivalent t o a single system of phase microscopy whose over-all magnification is equal to the product of the magnifications of the multipupil system and whose pupil function is the product of the complex pupil functions associated with each of the multipupils. The physical interpretation of the composite pupil function as a product is that the optical paths through corresponding areas of the multipupils are additive, while the corresponding amplitude transmissions are multiplied. This is another expected result. The theory will illustrate the usefulness of Fourier transformations in Considering problems of phase microscopy.
