instrumentation - American Chemical Society

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INSTRUMENTATION ;rs presented at Pittsburgh in the Symposium on Instrumental Analysis are dised and several new developments in the field of electronics are presented beg RalpH ίΤΉΕ Third Analytical Symposium sponsored b y the AnalytiA cal Division of the Pittsburgh Section of the AMEBICAN CHEMICAL SOCIETY was held on February 12 and 13. T h e gen­ eral details of this meeting are discussed in Chemical and Engi­ neering News and elsewhere in this journal b y Associate Editor Hallett. Our remarks a t this time are confined to the Sympo­ sium on Instrumental Analysis. The first session of this symposium was held on Thursday after­ noon, R. H. Mtiller presiding. After brief introductory remarks by Millier outlining the scope and concept of modern analysis as an essentially new science, a very interesting paper by Nelson Gildersleeve of the General Electric Co. outlined the instrument­ ing of physical methods of chemical analysis. This paper illus­ trated in very striking fashion the steps which must be taken in order to convert a typical laboratory measurement in physical chemistry to a form where it m a y be executed semiautomatically or even automatically—in any case, by relatively inexperienced personnel. Examples were chosen from the entire region of the electromagnetic spectrum: x-rays, ultraviolet, visible, a n d in­ frared. One consequence of the careful instrumentation of a physical-chemical technique resides in the comparative ease with which such procedures can be extended to automatic control. R. L. Garman of the General Precision Laboratory, Pleasantville, Ν . Υ., discussed the role of electronics in chemical instru­ mentation. This paper furnished a stimulating extrapolation into the future of chemical instrumentation in indicating the al­ most unlimited resources of the newer electronic techniques. T h e uses of supersonics, microsecond timing techniques, and microwaves were described. I n addition, all-electronic arrange­ ments for special measurements were discussed suitable for dielec­ tric constant determinations, trichromatic photometry, and Beer's law deviation compensators. Garman also described a circuit which marks the first fundamental advance in polarographic in­ strumentation—i.e., an amplifier coupled to an output cathode follower stage with R C damping in the latter stage. This permits recording polarographic diffusion currents with the complete elimination of oscillations and none of the difficulties ordinarily encountered when damping circuits are introduced in the circuit proper. The remainder of this paper was devoted to a brief sum­ mary of mechanical and electronic analog computers. This paper, like the first, emphasized the fact t h a t instrumental analy­ sis is not solely concerned with the use of existing instruments, b u t indicates t h a t new instrumental approaches arc available in abundance. The final paper, devoted to radioactive instrumentation and its potential use in routine analysis and process control, was pre­ sented by F . C. Ilenriques, Jr., Tracerlab, Inc., Boston, Mass. T h e fundamentals of radioactive measurements were carefully outlined, followed by a description of various counters, scaling circuits, and counting-rate meters. The future of radioactive techniques is assured b y the increasing availability of radioactive isotopes from the Atomic Energy Commission, the wide variety of measuring techniques, and the countless applications both physical and chemical, which the technique offers. Several un­ usual applications were discussed including the automatic regis­ tration of height of liquids in a column, layer thicknesses such as the coating of a wire with a thin layer of lead, or the thickness of metal foil as it is rolled. M a n y other applications concerned

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with automatic inspection are feasible and although alternative techniques are both feasible and possibly preferable, the radio­ active method has certain inherent advantages, particularly when the extraordinary sensitivity is concerned. All these appli­ cations require amounts of radioactive substances which present no health hazard whatsoever. The Friday morning session of the symposium dealt with a discussion of photoelectric spectrochemical analysis by J. R. Churchill, Aluminum Co. of America, New Kensington, Pa. This was prefaced by a description of excitation equipment and the general layout of a large industrial spectrographic laboratory. The two principal photoelectric spectrometers and uses in the routine analysis of alloys were described. A striking example of the stability and reproducibility of such equipment over long periods of time was amply illustrated by analytical data. The second paper, on x-ray diffraction, a fundamental analyti­ cal tool, was presented by H. P . Klug, Mellon I n s t i t u t e , Pitts­ burgh, P a . This lecture not only emphasized the distinctive advantages of x-ray diffraction and its ability to function as a nondestructive method of analysis but also gave a very compre­ hensive picture of stoichiometry and stereochemistry. The dis­ tinctive uses of the x-ray method were also emphasized in dis­ tinguishing between polymorphic forms and the identification and analysis of solid solutions. Applications of the x-ray spectrometer in qualitative and quan­ titative analysis were described by L. E. Alexander, also of the Mellon Institute. The advantages and some of the limitations of the Norelco Geiger counter x-ray spectrometer wore explained, and it was shown t h a t when the more important constituents of a crystalline mixture are wanted, the method is as valuable as the photograhic technique and considerably more rapid. Intensity measurements are more precise, and even for those cases involv­ ing components of unequal absorbing powers, suitable calibra­ tion curves can be prepared from a graded series of synthetic mix­ tures. . Specific examples were illustrated by the analysis of in­ dustrial dusts for quartz. A description of the Beckman flame photometer and its uses by Gilbert, Hawes, and Beckman was presented for the authors b y Haller, who told how this accessory to the Beckman quartz spectrophotometer may be applied to t h e analysis of over 40 elements. In the case of sodium, the sensitivity is a few parts per billion. With moderate consumption of gas and oxygen and a special burner which produces an essentially dry mist, sample is consumed a t the rate of 0.2 ml. per minute. Extensive d a t a were presented showing the effect of optimum wave length, dependence of oxygen-gas ratio, and other variables which control the pre­ cision and sensitivity. I n the Symposium on Modern Courses in Analytical Chemistry which was hold concurrently on Friday afternoon, M . G. Mellon of Purdue University presiding, two papers on instrumental analysis were presented by H. W. Safford and L. L. Merritt, Jr., dealing with the course offerings at the University of Pittsburgh and Indiana University, respectively. I t is to be hoped t h a t the authors will publish their papers soon, because both represent serious efforts to meet the defects in our present methods of teach­ ing analysis. Their pioneering efforts echo the early slogan of the Pittsburgh analysts t h a t it is "better to light a candle t h a n to sit and curse the darkness." Despite this, one wonders how our 2l A

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universities can continue in the thousand-year-old belief that they are the fountainhead of new knowledge. Current practice in modern analysis is far ahead, and there is excellent evidence to show that the gap cannot be closed by one or two well planned courses "tacked on" to an outmoded curriculum. The success of this two-day meeting was due in large measure to the unremitting labor of J. R. Anderson of the Mellon Insti­ tute, who was in charge of program details. Electronic

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General Electric Co. announces a new electronic tube suitable for the measurement of currents of the order of 10~ 15 ampere. The construction differs from the conventional tubes of this class in that it employs a dual control grid and duel anode and the response is essentially a differential one between the two halves of the tube. Transient and sporadic effects influence both parts similarly, and therefore reduce the influence of random fluctua­ tions. The tube carries the designation GL-5674 and has a fila­ ment rating of 3.8 volts at 0.090 ampere. Typical operation re­ quires a plate voltage of 6 and space-charge-grid voltage of 5 volts for a plate current of 20 microamperes per plate. Another important advance in electronics is marked by RCA's announcement of a special series of tubes designated as red tubes. This series is specifically designed for applications having rigid requirements for reliable and long tube life. They are guaran­ teed for a minimum life of 10,000 hours. The unique structural design and rigid tolerances account for highly reproducible char­ acteristics and long life, including, among other things, the ability to withstand shocks of 100 grams for extended periods. Three tubes in this series, the 5691, 5692, and 5693 are the red tube equivalents of the 6SL7GT, 6SN7GT, and 6SJ7 tubes, respec­ tively. Complete data on these tubes are available in booklet SRT-1001 from the Radio Corp. of America, Commercial Sec­ tion, BR 40, Harrison, N. J. Although this development will be welcomed by the designers and users of instruments, it is important to note t h a t design engi­ neers have, for a long time, obtained extremely long tube life by the use of conservative circuit design and operation of all tubes somewhat below their optimal rating. This has proved particu­ larly sound and economical in the design of industrial equipment where reliable and trouble-free performance is mandatory. A striking contribution to the general field of computing ma­ chines is described by H. W. Fuller of Harvard University [Electronics, 21, 98 (1948)]. Over and beyond specific use in computers, the paper describes an array of tube circuits which can synthesize the Arabic numerals from 1 to 0 for instantaneous pres­ entation on a cathode ray oscillograph together with means for presenting them in any desired sequence. In our opinion, there are many uses for the repeated or even instantaneous presenta­ tion of data, numerical sequences, or identifying pulses bearing a definite relationship to each other in time, magnitude, or polar­ ity. I t is not unusual to find t h a t conventional tube circuits re­ peatedly become complex and bulky as the information to be pre­ sented is complex. Long before such a state is reached, it be­ comes profitable to consider the advantages of cathode ray scan­ ning as a simple and versatile substitute [R. H. Millier, ANAL. CHEM., 19,74

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In a recent issue [Electronics, 21, 140 (1948)], R. S. Mackay of the University of California describes a simple but precise nonlinear indicator for vacuum gages. The circuit combines a Philips cold cathode ion gage with a 6E5 electronic indicator tube. The circuit can be arranged so that the electronic eye closes abruptly when a vacuum enclosure is pumped down to a preset pressure. The adjustment to various pressure ranges can be made very easily by shifting the bias on the indicator tube.