A N A L Y T I C A L CHEMISTRY
958
the calcium prdsent in the extract. Results obtained by this method appear to be a t least as accurate as, and probably more acrul-ate, than those obtained using the J. Lawrence Smith method, and the time necessary to complete the analysis is cut in half.
be used for qualitative and quantitative determinations. Neutron spectrometers useful in such studies were described. Both neutron transmittance measurements and radioactivation by neutrons already have been applied successfully to a number of analytical problems.
Factors Affecting Precision in Spectrochemical Analysis with buffers. PAULE. LIGHTY,Lime Crest Research Laboratory, hewton, IG J. ’II i ii~a~irlt~r in u hich precision and accuracy are affected by hi&r ri~atwid1 and concentration, sample fineness and matrix, t Iwtrcde grometry, gap length, current constancy, internal standard, linr psiis, and pretreatments of sample, was studied, and a method 1%a b evolved which provides standard deviations of 10% 01 batter for the elements and materials investigated. The method adopted resembles in some respects those des~iikxdbs Harvey (Harvey, C. E., “Method of Semiquantitat i l e Specliogrrtphic Analysis,” Glendale, Calif., Applied Research Irnbolritorics,1047), and by Weaver and Brattain [Weaver, J. R., a d Lhttain, 1C R , ANAL CHEM.,21, 103841 (194911, in that littiiunl c2trbonate io used as a flux, but the errors are reduced to thc riimerisio~iiof a quantitative system by the use of nickel as an mtc-rnttlstmd;trd, and adherence to other conditions is found to be fulrc’t ionally important.
Radio Frequency Mass Spectrometer. WILLARDH. BENXational Bureau of Standards, Washington, D. C. A mass spectrometer has been developed which uses velocity selection rather than magnetic deflection. A low voltage radio frequency alternating potential is applied to each of three grids of a fourteen-grid tube. The operating principles were described and some of the results obtained with the instrument were presented.
NEW SPECTROSCOPIC METHODS OF ANALYSIS
betermination of Sulfur in Petroleum Fractions by X-Ray Atlantic ReAbsorption. Y. W. LEVINEA N D A. H. OKAMOTO, fining Co., Philadelphia, Pa. A Geiger-LIiiller spectrometer has been used for absorption nlemurements to determine the sulfur content of petroleum fractions. The sulfur content is calculated from the difference in absorption between the sample and a pure hydrocarbon standard of approximately the same density. The method minimizes uncertainties due to variations in the carbon-hydrogen ratio of the sample and to fluctuations in the intensity of the x-ray beam, so that an accuracy of 0.02y0 sulfur can be attained for samples coritaining 1e.s than 2% sulfur. &Ray Fluorescent Analysis. LO-CHINOCHANG,Columbia University, New York, N. Y. The speaker discussed the theoretical background, the equipment outlay, advantages, limitations, possible errors, and a plicstlons of the x-ray fluorescent method of analysis. TRi method was related to the quantitative determination of elemeirt,s in metallic and nonmetallic substances. Neution Spectroscopy in Chemical Analysis. T. I. TAYLOR, Columbia I’iiiversity, Xew York, N. Y. A reuiew o f the 1)roperties of neutrons and their interactions with matter shows a number of possible applications to chemical analysis. As the velocity or the wave length of neutrons is changed, interesting variations are found in the magnitude and the nature of these interactions. Resonance absorption occurs for many elements at particular neutron velocities and these may
NETT,
INFRARED SPECTROSCOPY
Report of Activities and Progress of the Infrared PunchCard Committee. CARROLL CREITZ,National Bureau of Standards, Washington, D. C. Arrangements with the National Research Council for handling the committee’s finances are proceeding satisfactorily. A card identical with that adopted last year is now available for handplotting spectra. The Wright-Patterson Air Force Base has, by means of a fund transferred to the National Bureau of Standards, initiated the production of punch cards bearing infrared spectra. Data, for the bibliographic cards are being checked against existing bibliographies. Solicitation of spectra for inclusion in the file was made. Spectra of compounds of reasonably high purity and on which physical propwties have been determined are especially desired. Directiop for preparation of spectra for printing were given. Infrared Spectrometer with Cathode Ray Presentation. H. POWELL, AngleIranian Oil’ Co., Sunbury-on-Thames, England. An infrared spectrometer with visual presentation on a longpersistence cathode ray tube and suitable for use in an industrial laboratory was described. The performances of the instrument with a Bell Telephone Laboratories thermistor bolometer and high speed Hilger-Schwarz vacuum thermo ile, respectively, as radiation detectors were illustrated by rererence to traces of hydrocarbon spectra. The effects of band width of the display unit and of seanning speed on the over-all resolution of the spectrometer were also illustrated. The resolving ower a t the present rate of scanning, which covers approximate& 3.0 mu anywhere in the region 2 to 15 mu in 12 seconds, is considered sufficient for most work on hydrocarbon molecules.
A Direct-Recording Infrared S ectrophotometer Utilizing Memory Standardization. W. S. ~ A L L A W A Y , National Technical Laboratories, South Pasadena, Calif. The application of the memory standardization technique for the recording of infrared spectra directly in per cent transmittance was discussed. The problems involved and the advantages to be gained by this approach were considered and some performance curves of the Beckman instrument were presented.
Symposium on Thin Films F. A. HAMM, General Aniline & F i l m Corporation, Easton, Pa.
HIS Symposium on Thin Films, the third of an annual series Tof symposia sponsored by the Armour Research Foundation of Illinois Institute of Technology, was held a t the Sheraton Hotel, Chicago, Ill., on June 8, 9, and 10. The prior Symposia on Light and Electron Microscopy and on Resolution and Fine Partides formed an appropriate background, so that the subject of thin films was a natural sequel in what promises to be an interesting series of related meetings. The familiar sight of many of those who attended the earlier Armour symposia plus the appearance of new faces representing many walks of science lends weight to the idea that thin films are of considerable general interest. Some 200 people representing many branches of chemistry, physics, and engineering shared their knowledge in a cooperative and pleasingly informal way. Last year’s symposium a t which no formal papers were read had been considered as an experiment. The same atmosphere in which informality and spontane-
ous audience participation prevailed was thoroughly enjoyed again this year. Success in the experiment has been realized; consequently the Armour Research Foundation would do well to consider the continuation of this novel technique for conducting a meeting. The cochairmen, W. C. McCrone and C. F. Tufts, organized the program so that the various technical aspects of the general subject of thin films were properly evaluated. These aspects were discussed a t four sessions appropriately labeled formation, geometry, structure, and problems and applications. The chairmen for these sessions were R. D. Heidenreich, Bell Telephone Laboratories’; Henry Levinstein, Syracuse University; L. 0. Brockway, University of Michigan; and Allan T. Gwathmey, University of Virginia, respectively. A panel of “experts” had also been chosen to aid the chairmen. The choosing of aocalled experts must usually be done advisedly. This symposium
V O L U M E 22, NO. 7, J U L Y 1 9 5 0 was no exception. It developed that many of the real experts were members of the audience. Fortunately they graciously, and with an air of good humor, cooperated in the dissemination of their pertinent knowledge. W. E. Mahin, director of research of the Armour Research Foundation, opened the symposium with a few welcoming remarks. Immediately after the first session on formation had been opened, it became apparent that the definition of terms and the assignment of parameters were no easy matter. After some deliberation and argumentation, i t was agreed that each individual was rightfully entitled to define what is meant by a thin film in t e r m of parameters that most appropriately suited the problem. Methods of detection and formation and specifications on geometry were outlined. Again these considerations might have been discussed a t great lengths because they are obviously almost unlimited in number. As a matter of gerieritl agreement it was concluded that thin films are interfaces between two other phases. These interfaces are coherent, have relative dimensions, and affect the surface properties, not the bulk properties. The evaporation of metals and dielectrics in general is of tremendous interest both commercially and academically. Structure and environmental factors affecting structure were discussed for several materials. Germanium when evaporated onto silica at 25” C. was shown by electron diffraction to be glassy. When the target was a t 400” C., the germanium deposit was crystalline. Furthermore, the deposit consists of large and small spheres, with the large spheres growing a t the expense of the smaller ones, when evaporation is continued. Thus growth must occur equally in ail directions. The higher vapor pressure of the smaller spheres a t the elevated temperature presumably accounts for their decrease in size. Furthermore, the heat of condensation and the degree of orientation for evaporated films of metals such as aluminum are greater if the condensing substrate is highly crystalline, as in the case of mica as compared with glass. The evaporation of metals such as silver and aluminum and dielectrics such as magnesium fluoride and zinc sulfide to form films of controlled thickness in the preparation of mirrors, monochromatic filters, dichroic filters, beam splitters, etc., was discussed from the standpoints of theory and practice. One enigma has still not been solved: how to prepare front-surfaced aluminum mirrors without pinholes. Furthermore, the oxidation of evaporated metal films cannot be prevented by surface coating. The well known relations between refractive index and thickness of film and reflectivity or transmissivity were illustrated with samples of filters, beam splitters, and mirrors. The formation of highly polished surfaces of metals by electrolytic polishing (anodic reaction) was also described. The surface of aluminum can thus be more highly polished than in any other way. Effects of grain size and oxide formation on the reflectivity and electrical resistivity of evaporated metal films are of interest, too. The presence of residual gases has only a second-order effect on the grain size and oxide formation. Thick films of many metals such as silver, gold, copper, and chromium have a higher electrical resistivity than thin films or the bulk metals because of their porosity. It was somewhat surprising to learn that gold “blacks” are not black because of their sponginess or particle size distribution. Small amounts of tungsten, up to 5%, cause the “black” appearance in a manner not fully understood. Thin films of organic materials were strikingly illustrated by the “dark” and “bright” series of interference colors produced by a wedge film of barium stearate on glass. Monolayers of this long-chain compound are about 25 A. thick. Complementary interference colors may be readily produced by varying the refractive index of the supporting medium to values above and below that of the oriented organic film. These step wedges of
Electron Microscope Society of America. n o t e i Statler, Detroit, Mich., September 14 to 18. Eighth a l i n d meeting Instrument Conference and Eilibit. Iiistruinent Society of America, Buffalo, N. Y . , Septenibzr 18 t o 22 Fourth Symposium on Andyticd Chemistry. I o;tisia,ia Stata University, Baton Rouge, Lit., January 2Y to February 1, 1951
