V O L U M E 21, N 0 . ’ 4 , A P R I L 1 9 4 9 LITERATURE CITED
(1) Doub, Leona;d, and Vandenbelt, J M., J . Am. Chem. Soc., 69, 2714 (1947). (2) Vandenbelt, J. hi.,and Doub, Leonard, private communication.
CHARLES J. KERN
Ferrous Metallurgy SIR: I n the February issue there was a bibliography connected with the article on “Ferrous Metallurgy” [Beeghly, H. F., ASAL. CHEM.,21, 241 (1949)l which contained a number of excellent references to the colorimetric determination of molybdenum. I should like to offer as an addition to this list an article by George M. Poole, chief chemist of the Ingersoll Steel and Disc Division of the Borg-Warner Corporation, New Castle, Ind. [Iron Age, 148, No. 15, 62, 164-5 (1941)]. This is an excellent article and well worth including. L. A STARRETT 167 Webster Park Ave. Columbus 2, Ohio
Optical Society of America HE Optical Society of America held its winter meeting a t Tthe Hotel Statler, Kew York, 1;. Y., March 10 to 12, 1949. The program included a Symposium on Luminescence and contributed papers on vision, general optics, color, infrared, ultraviolet microscopy, and spectroscopy. The papers of particular interest to analytical chemists are abstracted here.
An Automatic, Continuous Tristimulus Integrator. H. R. DAVIDSOS AND L. W. IMM, Central Research Laboratory, General Aniline & Film Corp., and Librascope, Inc., Easton, Pa. An automatic tristimulus integrator has been developed for use with the General Electric recording spectrophotometer. Selsyn transmitters mounted on the spectrophotometer relay the wave length and reflectance to the computer where integration is carried out by means of mechanical analog techniques developed during the war. The integrations are performed continuously while the curve is being drawn a t either fast or slow speed. Tristimulus values for any curve may, therefore, be obtained by the spectrophotometer operator with no additional expenditure of time other than that required to record the values and return the counters to zero. The precision of the prototype computer is about ~ 0 . 0 0 0 5&-hen the tristimulus values are so normalized that Y=l.OOOO for a sample whose reflectance is 100%. The combination of spectrophotometer and integrator is a t least as sensitive and usually more sensitive than the eye for the detection and evaluation of small color differences. The absolute accuracy of the tristimulus values obtained is approximately +0.001. Examples were given to indicate that this high speed computer, which will be available commercially, makes practical the application of numerical methods to the solution of color problems. Tristimulus Computation in the Dyestuff and Textile Field. I. H. GODLOVE, General Aniline & Film Corp., Easton, Pa. The tristimulus integrator described by Davidson and Imm has been found, because of its high precision and saving of time, t o yield many results of interest t o the textile dyeing field not conveniently obtained previously. It permits statistical analyses7 for example, obtaining a measure of “unlevelness” (nonuniformity) of dyeings. The average differences between the trichromatic coefficients x and y for A.M. and P.M. repeats on six red wool dyeings were 0.0004. This includes the over-all errors due to the spectrophotometer itself, the positioning of samples, and the integrator. Other work indicates that the precision is adequate for small-difference colorimetry. Work has been done on liquid and film filters to yield analyses for night lighting as well as daylight, “change of shade in artificial light” being of much interest to dyers. Results contrasting additive mixing on a “union” (cotton and wool) dyeing and the subtractive mixture of dye solutions, were shown; also studies on “dyer’s brightness,”
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which is related to saturation. The computer has also been used to follow the striking changes of color due to aggregation of dye molecules in solution; this and other dye phenomena were illustrated. Performance of a New Double Beam Infrared Spectrophotometer. JOHN U. WHITE ASD M.4x D. LISTON, The PerhnElmer Corp., Stamford, Conn. A new recording infrared spectrophotometer has been constructed and tested under a variety of operating conditions. Resolution has been observed approaching the theoretical limit for the rock salt prism used. Stability corresponds to 1.5 times the Johnson noise of the thermocouple used as detector, or to an to 0.5 X watt, r.m.s. equivalent noise input of 1.5 X depending on the speed of response. The variation of IO with wave length is small, and the scattered light is kept to less than 1% throughout the useful range. The instrument’s performance was illustrated with spectra measured under conditions showing its versatility in such variables as resolution, speed, and stability. A Rapid-Scanning Spectrometer for the Kear Infrared. B. W. S. SILVERMAN,Applied Physics Laboratory, i n e Zoiiris Eiopiiina ’u’riiveiaiGy,Baltimore, Md.
BPLLOCKAKD
A scanning spectrometer has been built for use in the lead sulfide region. Suitable spectra in emission as well as in absorption have been obtained a t scanning rates up to 120 spectra per second in the region 360 millimicrons to 3 mu. Scanning time per cycle is approximately 20% of the total cycle. Scanning is achieved by oscillating the Littrow mirror of the spectrometer, using a torque motor and direct link as the driving mechanism. This results in an approximate $ne wave oscillation with a maxiWith lithium fluoride optics. mum usable amplitude of 1.5 the region 1 to 3 microns can be covered in a single range. Preliminary results have also been obtained with a rocking grating as the dispersive element. Resolving power limitations are set by the time constant (approximately 30 microseconds) of the Pb-S cell and amplifier. A liquid air-cooled Pb-Te cell was tried in the instrument; however, the long time constant (1 to 2 milliseconds) required a decrease in scanning speed to a few cycles per second.
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Infrared Absorption Spectra of Ten Substituted Methanes. EARLEK. PLYLER AND W. S. BENEDICT, National Bureau of Standards, Washington, D. C. The infrared absorption spectra of CHCls, CHBra, CHI,, CH2C12, CH& CHBrC12, CHBrZCl, CBrC13, CBr2C12,and CClr have been measured in the region from 2 to 38 mu. Chloroform and bromoform were investigated in the vapor state and in the liquid state. A comparison of the spectra for the two different states reveals only small shifts in the wave lengths of the bands. The spectra of the other compounds were obtained in the liquid state or in solutions. Cell thicknesses from 0.05 to 2.0 mm. were used. The thick cells made it possible to observe many combination bands. The observed bands have all been interpreted as fundamentals, combination and overtone bands, and difference bands. In the compounds with similar structures, the relative intensities of the various bands show regularities. The fundamentals may be assigned to different symmetry types, on the basis of a normal coordinate treatment, using force constants similar to those reported by Decius.
A Color-Translating Ultraviolet hlicroscope. Polaroid Corp., Boston, Mass.
E. H. LAND,
The translating ultraviolet microscope is a highly specialized apparatus designed primarily to aid biophysicists in identifying cell structures. Not only is the resolution of the ultraviolet microscope approximately twice that of the visible light microscope, but the complex organic molecules in tissue cells exhibit their own specific absorption spectra in the ultraviolet. This new microscope utilizes this latter phenomenon to record the absorption data, thereby “fingerprinting” the specimen. This instrument is still in the development stage; probably the time factor (almost a minute) to record the absorption on photographic film will eventually be reduced considerably. At present several sources of ultraviolet are being used; the G. E. light pressure mercury arc (H-6) enjoys some favor because it provides a continuous and discontinuous spectrum. A Wadsworth (diffraction grating) type of monochromator is used t o isolate the desired wave lengths (over very narrow regions). Refracting components of quartz and fluorite have been added to the Schwarzschild mirror type of microscope objective so as t o
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obtain larger numerical apertures with better chromatic correction. The image is recorded on 35-mm. film which is processed in the instrument and may then be projected onto a fluorescent screen. Living cells require photography because not more than about 4000 ergs of the 2650 A. line can be tolerated. Use of this instrument necessitates the formulation of a catalog or atlas of absorption data from a large number of molecules. In identifying an unknown, reference is made t o this atlas. The preparation of this reference atlas is carried out experimentally and is undoubtedly very time-consuming. An absorption curve between 220 and about 360 mu is plotted. Certain strong absorptions in the ultraviolet correspond to specific colors (absorptions) in the visible. Hence the reason for the “translation”-for example, if the maximum absorption is at 260 mu, equivalent to blue in the visible, the crystal may appear yellow (minus blue). In practice the ultraviolet absorptions corresponding to the three visible primary colors (red, blue, and green) are translated. This instrument represents a rather ingenious development, and is probably the most significant contribution t o ultraviolet microscopy since Kohler’s work during the early part of this century. However, the technique is specialized and may enjoy only limited applications to cell structures of relatively larger dimensions.
ANALYTICAL CHEMISTRY quantitative spectroscopic analysis is generally an appreciable fraction of the total analytical time. This can be reduced considerably by the use of a new coordinate paper on which the plot of transmittance versus relative exposure is approximately a straight line for all the common emulsions. By the use of this aper, the need for the (1-transmittance) portion is eliminated. b h e n it can be established that the calibration on this paper is a straight line, the number of calibration points can be reduced. The new emulsion calibration paper has a logarithmic abscissa and a modified logarithmic ordinate which expands nonuniformly from about 30 to 97% transmittance. The approximate linearit of emulsion calibration curves for Eastman SA-1 films, i4-1 plates SA-2 films, I-N plates, and 33 plates, between 2 and 97% transmittance, has been verified with data from five independent laboratories. A method was described for eliminating all emulsion calibration procedures when standards are placed on the same plate or film with unknowns.
A Laboratory-Cast Pin Sample for the Spectrographic Analysis of Copper-Base Alloys. E. W. PALMER, J. P. IRWIN, A W C. C. FOGG, The American Brass Co., Waterbury, Conn.
A practical and inexpensive method has been developed for preparing pins of standard size and shape from any form of metallic sample (wire, sheet, heavy bars, drillings, etc.) received for s ectrographic analysis by a brass mill laboratory. The sampye is reduced to fine chips and a small portion (approxiColor-Translating Ultraviolet Microscopy aiid Ultraviolet mately 1 gram) is remelted under argon in a specially designed Spectrophotometry. ELKANR. BLOUTAND MIRIAMS. FLOWER, graphite crucible which also serves as the mold in which the Research Laboratory, Polaroid Corp., Boston, Mass. sample is solidified. The crucible and contents are heated in a small laboratory electric arc furnace. Sample pins so prepared Ultraviolet absorption spectrophotometry has been extensively are machined to dimensions that vary with the excitation to be used in the characterization and identification of many materials. used and the elements to be determined. Even for alloys conThe procedures used in the Polaroid laboratory for color-transtaining easily oxidized or easily vaporized elements, in the lating ultraviolet microscopy, and in particular some of its amounts usually encountered, the pin sample satisfactorily reapplications to biological, organic, and pharmaceutical chemistry flects the composition of the material prior to remelting. Repliwere discussed. By taking photomicrographs of materials under cate analyses can be made on the same pin by remachining. Becontrolled conditions at three different wave lengths in the ultracause the high conductivity of copper-base alloys makes these violet and then projecting simultaneously the images so obtained materials unusually sensitive to changes in electrode size and through three visible additive color filters, one obtains a colored shape, this development of a standard sample makes possible, representation of the material in which the color de ends on its for the first time, really quantitative spectrographic work on the inherent ultraviolet absorption. Variables involvef in the use wide variety of forms and gages of alloys submitted to the brass of the technique, such as control of exposure times, photographic mill spectrographer. development and specimen size, were discussed, and the advantages and disadvantages of this method were compared with An Air Interrupter for Use with an A.R.L. Spark Sourcr. ultraviolet absorption spectroscopy and spectrophotometry. EMIL KACZOR AND KATHERINE CHAMBERLAIN, Wayne UnivcrExamples and comparisons of ultraviolet spectrophotometry sity, Detroit, Mich. and color-translating ultraviolet microscopy from the fields of biology and biological chemistry (tissue sections, nucleic acid, Substitution of an air interrupter for the rotary gap on this proteins, and amino acids) and organic chemistry (aromatic spark source is not practical, as the transformer lacks power t o acids, purines, pyrimidines, fibers, and high-polymer films) were charge the capacitors to sparking potential several times per presented. cycle. B separate unit was described that is powered by the transformer in the original unit. Changeover from conventional Spectra of the Heavy Elements. FRANK S. TOMKINS AND operation with the rotary gap to air interruption is rapid and MARKFRED, Argonne National Laboratory and Armour Research convenient. An inductively coupled pickup was also described Foundation, Chicago, Ill. for obtaining oscilloscope patterns indicating voltage and current conditions in the leads to the analytical gap. To study single The spectra of the new heavy elements are characterized by patterns, a camera synchronizing attachment has been built that great complexity similar to that well known for thorium and makes it possible to photograph a single trace on an ordinary uranium. Consequently, description of the spectra to be adeoscilloscope with green medium persistence screen. An Eastman quate for term analyses and assignment of electron configurations twin lens reflex camera was used. The moving contact that is must be extensive, containing complete, accurate wave lengths built into the shutter closes the circuit to charge a condenser and much other material. Because considerable effort and after the leaves are fully open. This potential is applied to the amounts of sample are required it will be some time before such horizontal plates of the oscilloscope and produces a single sweep descriptions are available. On the other hand, it wouM be useful across the screen. The shutter time is made long enough to take for spectrochemical analyses to have wave lengths t o 0.1 1.and advantage of the full persistence period of the trace. Fully intensities in a convenient spectral region, and this information exposed photographs of single sweeps can be obtained in t h i s has been collected for protactinium, neptunium, plutonium, and way on Verichrome film. americium. Intensities for each line were obtained as the reciprocal of the limiting dilution a t which it could be seen with the New Techniques in the Spectrochemical Analysis of X o u copper spark source, and therefore the same intensity scale is metallic Samples. M. F. HASLERAND C. E. HARVEY,-4pplicd used for each element. Hence it could be observed that the Research Laboratories, Glendale, Calif. spectrum of americium appears to stand in the same relation to those of the other heavy elements that the spectrum of europium Several new techniques have been developed which greatly does to those of the preceding rare earths, both elements conextend the range and application of spectrochemical methods in taining relatively few lines of high average intensity. This sugnonmetallic sample analysis. The first has to do with a method gests by analogy that Am I contains seven f electrons plus two of vaporizing and collecting a nonmetallic sample in a manner others. which reduces it to a standard chemical and crystallographic form. By this means, samples and synthetically prepared standards can be reduced to a common form which allows analysis by Emulsion Calibration Paper for Quantitative Spectroscopic various high precision spectrochemical methods. The second is a K. HUGHESAND R. W. MURPHY,Technical Analysis. HAROLD method of eprtrking to the edge of a rotating disk, which is a Service Department, Socony-Vacuum Laboratories, Paulsboro, briquet containing a nonmetallic sample mixed with a binder. N.J. This method of sparking allows results of high precision to be The time devoted to collecting and lotting the required data obtained, providing the correct binder, discharge conditions, and in anv of t,he well-known methods oremulsion calibration for rotational speed of the disk are employed. A combination of
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V O L U M E 21, NO. 4, A P R I L 1 9 4 9 these two techniques has been utilized to solve the difficult problem of mica analysis. A method has been developed which allows analysis of both major and minor constituents with an accuracy of 2 to 3% of the amount present. A similar method has been used to extend alkali determinations in cement down to 0.01% with greatly increased accuracy, yet utilizing spectrum lines in the ultraviolet and violet.
New York Academy of Sciences HE
Section of Physics and Chemistry of the New York Acad-
Temy of Sciences held a conference on specific methods of
analysis on March 25 and 26, at which the following papers were presented. These papers will be published as a monograph. An abstract of the last paper is given here because it deals with a subject which, although not entirely new, has not received the emphasis which its place in analysis deserves. X-Ray Absorption and Chemical Analysis. HERMANA. LIEBHAFSKY,Research Laboratory, General Electric Co., Schenectady, N. Y. Analytical Specificity of Countercurrent Distribution. J. DELAFIELD GREGORY AND LYMAN C. CRAIG,Rockefeller Institute for Medical Research, New York, N. Y. Methods and Application of Differential Thermal Analysis. RALPHE. GRIM,State Geological Survey, Urbana, Ill. Optical Properties of Surface Films. ALEXANDRE ROTHEN, Rockefeller Institute for Medical Research, New York, N. Y. Goniometric Analysis of Crystals. J. D. H. DONSAY,Johns Hopkins University, Baltimore, Md. Analysis of Mixtures Based on Rates of Reaction. LEE, University of Minnesota, Minneapolis, hlinn.
THOhfAs
8.
If two compounds react with a given reagent a t different rates it is frequently possible to base a method of analysis of mixtures of the two compounds on this difference. The method is useful chiefly in the analysis of mixtures of two organic compounds that contain the same functional group. The principles involved are illustrated in an analysis of mixtures of ethyl and isopropyl acetates which is based on a difference in rates of saponification. The total ester content of the sample is determined. A reaction mixture is prepared in which the total molar ester concentration is specified-e.g., total ester concentration is 0.100-and the initial concentration of alkali is also specified. The mixture is allowed to stand for a specified reaction period and the concentration of hydroxyl ion remaining is then determined by acidimetric titration. The concentration of hydroxyl ion remaining is compared with a calibration curve that gives directly the initial composition of the mixture. Thus, two titrations (the determination of total ester content of the sample, and the determination o f hydroxyl ion remaining a t the end of the reaction period) are dufficient to establish the original composition of the mixture. In general, the simultaneous reactions upon which the analysis of mixtures is based are called homocompetitive reactions, homo referring to the fact that the two compounds that constitute the mixture contain the same functional group. The homocompetitive reactions may be second-order reactions (as in the case of saponification of esters) or first-order reactions (as in the case of the decomposition of two aldehyde bisulfite addition pxoducts). I t is possible to treat the kinetics of two homocompetitive reactions in a n exact theoretical way. From this treatment it is possible to calculate calibration curves for the analysis of mixtures on an entirely theoretical basis, provided that the values of the two specific rate constants are known. (It is also possible, and often desirable, to establish the calibration curve empirically by analyzing mixtures of known composition.) The accuracy of the method of analysis is dependent on several factors. Ratio of Specific Rate Constants of the Two Reactions. In general, the ratio of the rate constants should be 4 to 1 or greater if the analysis is to be made with ease. If the ratio of rate constants is 1 to 400 or greater, and if a suitable reaction period is chosen, it can be assumed that one of the two compounds reacts quantitatively during the reaction period and the other compound does not, practically speaking, react a t all. In such a case a calibration curve is not necessary and the analysis is simplified. Reaction Period. For any given pair of homocompetitive reactions there exists an optimum reaction eriod for the analysis mixtures. The optimum reaction period Jepends on the values
of the rate constants of the two reactions and is calculated from the equations Second-order reactions: First-order reactions:
top$. = t,,,t,
rn k" TO
-In (k"/k ') = ro(k' - k " )
where k' and k" are the specific rate constants of the two reactions and re is the initial concentration of the reagent. Temperature at Which Reactions Are Carried Out. In general, the ratio of specific rate constants of two homocompetitive reactions increases with decreasing temperature. The following relation is usually applicable regardless of whether the reactions are second order or first order: k' constant log 7 = ___
k
T
where 1' is the absolute temperature. The homocompetitive reaction method has been applied to the analysis of several types of mixtures. Mixtures of Esters. The relative rates of saponification of methyl, ethyl, isopropyl, and tert-butyl acetates at 25' C. are in the ratio of 119:72:17:1. The relative rates of saponification of methyl formate, acetate, monochloroacetate, and dichloroacetate a t 25 O C. are in the ratio of 223: 1:761 : 16,000. From these values it is seen that the analysis of many pairs of esters is possible. As an example of the analysis of compounds that do not react with the reagent a t greatly different rates, mixtures of ethyl acetate and isopropyl acetate were analyzed and the results were compared with the calibration curve calculated from the two specific rate constants. The theoretical curve agreed with the experimental points within 1 to 2%. The average deviation (error) in analysis of mixtures of the two esters was 1% (absolute). Mixtures of Olefins. The rates of reaction of perbenzoic acid with the following types of olefins, RCH-CH2, RC(CH3)CHI, RCH-CHR, and RC(CHa)-CHR, at 25" C. (mixture of chloroform and benzene as solvent) was found to be 1:25 :30: 400. Thus it is possible to analyze mixtures containing two different types of olefins. An interesting application of the analytical method was made in the determination of "internal" and "external" double bonds in various types of synthetic rubbers. Mixtures of Carbonyl Compounds. Analysis of mixtures of carbonyl compounds might be based on rates of formation of aldehyde and ketone bisulfate addition products. However, in general, it is preferable to base the analyses on rates of decomposition of the addition products. The rates of decomposition of formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, and acetone bisulfites were found to be in the ratio 1:60:160:1600:400 (at 25OC. and p H 3.4). As an illustration of the analytical method mixtures of acetone and formaldehyde were analyzed. A preliminary investigation of the effect of pH on the rates of decomposition disclosed that the ratio of rates of decomposition was very large in solutions of high acidity. Thus in 1 .V hydrochloric acid a t 25" C. the rates of decomposition of acetone bisulfite and formaldehyde bisulfite are in the ratio of more than 10,000 to 1. Analyses of mixtures of the two carbonyl compounds yielded results accurate to a t least 1%. It is expected that analysis based on homocompetitive reactions will be used chiefly for mixtures of homologous organic compounds, especially of methyl and ethyl compounds; mixtures of primary and secondary, or of secondary and tertiary organic compounds; mixtures of ortho and para isomers, etc.; mixtures of different types of ethylenic compounds; mixtures of nionochloro and dichloro organic compounds, etc.
Instrument Society of America. Royal York Hotel, Toronto, Canada, May 12 and 13, 1949. Second Annual Summer Symposium on Analytical Chemistry. Wesleyan University, Middletown, Conn., June 24 and 25, 1949. Fourth Instrument Conference and Exhibit. Municipal Auditorium, St. Louis, Mo., September 12 to 16,1949. I
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