INSTRUMENTATION A report on papers presented in all-day Symposium on Instrumental Methods of Chemical Analysis, sponsored by New York Section of American Chemical Society by Ralph continues unabated in analytical symposia. On November 20, the New York Section of the AMERICAN CHEMICAL SOCIETY sponsored an all-day Symposium on Instrumental Methods of Chemical Analysis. More than 500 chemists attended the sessions which were held at the Washington Square College of New York University. R. II. Millier presided and, after fitting introductory remarks by C. F . Rassweiler, chairman of the New York Section, and J. E. Vance, chairman of the Chemistry Department of New York University, the opening address was delivered by Associate Editor L. T. Hallett. In outlining the role of instrumental methods in modern analysis, the speaker traced the evolution of analytical techniques which has led to the numerous and diverse physical tools that now perform the majority of analyses. It was pointed out that the most elaborate instruments, despite their speed and precision, still depend to a large extent upon the maintenance of primary standards, criteria of purity, and other essentially chemical requirements. Hallett stressed the need for continuous effort in instrumental research, as distinguished from instrument application. The need arises from the fact that it is frequently necessary to modify an existing instrument or supplement it with additional devices to solve a special class of problems. In his opinion, a small development group, familiar with electronics, servomechanisms, and the general techniques of modern physics, is an indispensable part of an analytical research department. T. I. Taylor of Columbia University covered a remarkable amount of territory in discussing mass spectrometry and neutron spectrometry in modern analysis. The various applications of mass spectrometry were described, such as isotopic abundances required in problems of isotope separation, age determinations of minerals, exchange reactions, and tracer experiments. The isotope dilution method has been particularly valuable in biological research, especially in determining such compounds as the amino acids. For general gas analysis, particularly in the petroleum industry, as many as 15 different hydrocarbons can be identified and quantitatively determined in a sample no larger than 0.1 cc. In some of the speaker's researches on the catalytic exchange and addition of deuterium to butènes in relation to the double bond isomerization, the mass spectrometer was indispensable. In the uranium hoxafiuoride diffusion plant at Oak Ridge, mass spectrometers performed continuous analyses of gas
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streams [ANAL. CHEM., 20, 188 (1948)].
I t was pointed out
that when combined with the dilution method of flow measurement and with appropriate servomechanisms, mass spec-
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trometers may be used for automatic control of certain in* dustrial processes. The extensive use of neutrons in analytical chemistry seems to await only a convenient source of neutrons and t h e availability of neutron velocity spectrometers. Radioactivation with neutrons has already been applied to a number of analytical problems. Here the sample to be analyzed is immersed in a flux of neutrons, some of which are absorbed by the nuclei of the element to be determined. After suitable treatment, the radioactivity induced in the element is determined. This is a measure of the quantity of the element originally present in the sample. Taylor clearly outlined the variation in the interaction of neutrons with substances as the velocity of the neutrons is changed. At high velocities the effective cross section for neutron interaction is about 3 X 10~24 cm. 2 (3 barns). A t lower velocities, approaching resonance velocity, a marked increase occurs which may be as high as 10,000 barns in t h e • case of cadmium and indium. At still lower velocities an inverse variation begins and the slopes of the 1/v lines are distinctive enough in some cases for analytical purposes. A cooperative venture with Havens of the Columbia physics department was described involving a modulated cyclotron source of neutrons with a time-of-flight velocity selector. These are startling developments, presaging a new" era in analysis, b u t the techniques have already shown their value in such difficult analyses as tantalum in columbium, hafnium in zirconium, rhodium in platinum, and hydrogen in fluorocarbons. R. C. Gore of the American Cyanamid Co. presented an enormous amount of information in rapid fire order illustrating the applications of infrared spectroscopy to organic chemical problems. After an orderly, logical presentation of the fundamental principles and a discussion of equipment and means for modifying existing instruments for special problems, he illustrated specific examples in great numbers. The peculiar advantages of heavy and ordinary water as solvents were shown to be very useful, despite the fact t h a t one ordinarily assumes that aqueous solutions are useless in the infrared. As an excellent example of the great amount of work being done in this field, the speaker pointed out that the monograph of which he is co-author was out of date before it was published and that at present more than 20,000 infrared patterns are known and the list still grows. He also gave an account of a useful polarization attachment which uses thin selenium films mounted at t h e Brewsterian angle with respect to the optic axis. 23 A
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ANALYTICAL
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Splash guard opened showing jet pipe for coolant; a companion jet is on the opposite side of the wheel.
A laboratory siie cutter with ample power for fast cutting of samples up to 1 " in diameter.
This cut-off machine is built with the usual Buehler emphasis on precision in both the construction of the machine itself and the work it performs. The con trols are arranged for the utmost convenience of the operator — a feature that contributes to speed and accuracy in cutting samples.
Complete view of cab inet showing storage bin for extra wheels and tools.
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The cutting wheel mounted directly on the ball bear ing motor shaft is free from side play or vibration and is cooled by a stream of coolant directed on both sides of the wheel under the guard. The cutting is done on the front of the wheel by using the long lever handle to raise the clamp base holding the sample to contact the wheel. This mechanism is bal anced so that pressure against the cutting wheel is under perfect control at all times by the operator. A metal splash guard, removed in the illustration, furnishes pro tection from spray. Overall dimensions are 24" χ 28" χ 50". Shipping weight, 575 lbs. THE BUEHLER LINE OF SPECIMEN PREPARATION EQUIPMENT INCLUDES . . . CUT-OFF MACHINES · SPECIMEN MOUNT PRESSES · POWER GRINDERS · EMERY PAPER GRIND ERS · HAND GRINDERS · BELT SURFACERS · POL ISHERS · POLISHING CLOTHS · POLISHING ABRASIVES
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METALLURGICAL APPARATUS H 5 WEST WACKER BRIVS, CHICAGO 1, ILL.
CHEMISTRY
An interesting and enlivening account of x-ray diffraction as an analytical tool was given by I. Fankuchen of the Brooklyn Polytechnic Institute. As a physicist, the speaker admitted his reluctance in saying that 90% of all x-ray meas urements are concerned with analytical problems of one sort or another. Although several excellent x-ray analysis instru ments are available in this country, in his opinion there is a dearth of good single crystal x-ray goniometers and the im ported versions are much better than ours. The speaker also described some of his work on microcameras and a twin crys tal spectrometer. The great need for an extensive revision of x-ray data was pointed out and the unusual value of the x-ray method as a means for determining molecular weights was emphasized. Some of the distinctive analytical applications of electron diffraction and electron microscopy were described by Κ. Η. Storks of the Bell Telephone Laboratories. Examples of the various techniques for specimen preparation were described, such as mulling powders in parlodion for dispersion and film casting on slides. An interesting case, illustrating the need for reference to alternative methods, was one in which x-ray examination had shown the presence of nickel whereas the electron diffraction pattern showed definitely that nickel ox ide was present. P. P. Debye, also of the Bell Telephone Laboratories, de scribed particle size determinations by light scattering, a technique which has been so useful in studying macromolecules. It has been possible to extend the technique to sys tems of molecular weight as low as that of sucrose. After describing the theory of light scattering and the special photometers required for the measurements, the speaker de fined the dissymmetry coefficient, obtainable by measuring the scattering intensity at 45° and 135° to the optic axis. He also discussed the interpretation of scattering data in terms of the behavior which is to be expected for spherical, rodshaped, and coiled molecules, respectively. Instruments, techniques, and applications for radioactive isotopes were described by B. Schloss of the Nucleonic Sales Co. An excellent summary of the fundamental concepts and techniques of nuclear physics was followed by demon strations with scaling equipment. Lack of time unfortu nately hampered the speaker, but still permitted the audience to gain a clear, systematic picture of this important field. Informational Advertising We wish to acknowledge the important aid which many in strument manufacturers and dealers are giving analysts and the entire field of analytical chemistry, by supplementing their advertising with literature references and helpful hints. We hereby assume the calculated risk of singling out one of these and know with certainty that we shall receive many reproofs for neglecting others who have been equally helpful. Walter Burfischer of the AVilkens-Anderson Co., I l l North Canal St., Chicago, has issued another set of "Curves and References"—a compilation of literature abstracts, helpful hints, and breezy comments on spectrophotometric deter minations. They are classified according to the type of analysis: steel, water analysis, vitamins, clinical, etc. A number of publications are also listed, some of them free and others at regular publishers' rates. These references deal primarily with methods adaptable to the Coleman and Klett instruments, but are valuable to anyone concerned with opti cal methods of analysis. We wonder if all advertising managers are aware of the good will which this class of service engenders among the scientific public.
