INSTRUMENTATION Recent exhibit of instruments and apparatus at Instruments and Measurements Conference in Stockholm included almost every field of technical measurement by Ralph HE Instruments and Measurements and Exhibition which was held in Stockholm in the latter part of September attracted a large group from the Continent, Britain, and the United States. Time did not per mit our attending the conference, but we did have a brief view of the exhibit of instruments and apparatus at the St. Eric's Fair Grounds. The entire undertaking was sponsored by the State Council of Technical Research in co operation with the Royal Swedish Academy of Engineering Sciences and the Association of Technical Physicists. Almost every field of technical measure ment was represented by one or more exhibits including machine tool opera tion, meteorology, aerodynamics, tele communications, computing, and mate rials testing, with heavy emphasis on nuclear technolog3^. The latter was well represented by Norwegian exhibits and the French Government had a scale model of a nuclear reactor. A number of exhibits were of definite or indirect interest to analysts and a few of these might be discussed with profit.
T Conference
Study
of Critical
Phenomena
H. L. Lorentzen of the Oslo Univer sity Division of Chemistry has developed an instrument for the study of critical phenomena in which the irregular mass distribution in sealed-off tubes in which critical phenomena are taking place can be studied by refraction measure ments. The light source is a disk illuminated by a sodium vapor lamp. Metallic strips are placed vertically between the disk and sample tube. An optical arrangement on the far side produces a sharp picture of the strip. The refractivity gradient along the tube can be determined photographically by measurement of the distance between the imaged strips. A special thermo stat was developed utilizing the thermal
expansion of the thermostat liquid, the volume of which was about 1 liter. Temperature fluctuations were less than ±0.001° C. and magnetic stirring forced liquid through the chamber at a rate of 50 liters per minute without adverse mechanical vibration. The photoelectric scanning method for counting individual microscopic cells and particles was demonstrated by Dr. Lagercrantz of the Department of Medical Chemistry of Uppsala Univer sity. We described this technique some months ago in this column. I t con tinues to hold much promise for appli cations beyond the original intent. From the same institution an improved apparatus for the Dumas determination of nitrogen has been developed by W. Kirsten, in which a very high combus tion temperature (1000° C.) is employed. Nickel oxide is used and the combustion and sweeping are completely automatic. A standard deviation of 0.045 *~7ο i s
reported for this technique. Full de tails are to appear in Mikrochernie. An automatically recording surface balance using a dynamic gage as a pressure meter yields pressure-area curves on a standard electronic recorder. The equipment can be placed in a com pletely closed thermostatically con trolled container which allows the study of surface films under high three-di mensional pressure, since no optical or mechanical links between balance and recorder are necessary. Automatic
Distillation
Unit
An automatic distillation apparatus for moderate vacuum is a development of the Henkel Kemiskt Tekniskt AB of Stockholm and is based on Swedish patent No. 126,302 of K. J. I. Groth (1946). The instrument is based on distillation at constant temperature and by lowering of the pressure. A pen is fixed to that part of the pressuredecreasing device which moves verti 25 A
H.
Müller
cally downward when the contact ther mometer in the distillation head is ac tuated. The pen is pressed against a chart fixed on an aluminum plate which moves horizontally while the take-off valve is open. The resulting curve shows pressure vs. take-off quantity. An automatic sample receiver consisting of twenty glass tubes circularly arranged in a vacuum desiccator rotates slowly when the take-off valve is open. When the pressure-decreasing device is in operation, the take-off circuit is blocked in order to decrease the reflux ratio during fraction transitions. With this automatic apparatus 200 grams of fatty acid methyl esters are normally dis tilled in 48 hours. The Research Laboratory L.K.B. Stockholm has been responsible for much beautiful and precise equipment. The laboratory has recently studied means for improving the Westphal balance for rapid and precise density determinations. One which eliminates the error due to surface forces acting on the thread which supports the plum met, consists of a float containing an iron core and this is attracted down ward magnetically by a surrounding coil. Current through the coil is con trolled photoeleotrically by a beam of light which scans the float. Errors in density are less than 7 in the fifth decimal place. Two developments from the Depart ment of Physical Chemistry at Uppsala University stem from the design of Professor Claesson and G. Jacobson. One is an interference osmometer in which the two halves of an osmotic cell are connected to two vertical tubes where the menisci are observed interferometrically. This permits the meas urement of extremely small osmotic pressures. In another application, the concentration of a solution is observed interferometrically in a tube 400 mm. long for concentration as low as 0.01%.
ANALYTICAL
26 A
CHEMISTRY
INSTRUMENTATION
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The use is primarily for following the effluents of absorption columns. From the Research Institute of Na tional Defense in Stockholm comes an electronic instrument for pressure meas urements in physiology. It undoubt edly has many other applications. It is based upon the principle that pressure variations are translated into current variations by means of a mechanoelectronic transducer. A small pressure chamber is fitted with a very thin platinum membrane about 12 mm. in diameter. Deflection of the membrane is transmitted directly to the movable anode of an R.C.A. 5734 transducer tube. In this tube, microscopic changes in the position of the anode with respect to the other tube elements produce large changes in the anode current. Specifically, this manometer produces an output signal of about 1 volt for a membrane displacement of 0.002 mm. Several reports of this work, including constructional details and applications, have appeared in American journals, [Pettersson, H. J., and Clemedson C. J., Science, 111, 696 (1950); J. Lab. Clin. Med., 38, 631 (1952)]. Electronic
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Multiplier
Many computational devices of var ious degrees of elaboration have been developed by this agency, but few of them have any direct bearing on the interests of the analyst. One of these will be mentioned because it is an ex cellent application of a very useful general principle. P. Lundborn has devised an electronic multiplier which accepts two factors of either sign and delivers a d.c. output which is the prod uct of the two with correct sign and with an accuracy of 0.1%. In principle, it is an accurate pulse modulator. A square wave is amplitude modulated by a voltage representing one of the factors to be multiplied and width modulated by the other. The product is continuously available, in effect as the duty cycle which is at all times equal to the product of pulse height and width. If freely running, the repetition rate enters as a scale factor. Electrical multiplication is easily accomplished with adjustable voltage dividers, but the purely electronic equiv alent without moving parts is not too simply achieved. As a rule, summing (Continued on page 28 A)
28 A
ANALYTICAL
CHEMISTRY
INSTRUMENTATION amplifiers with logarithmic inputs are required. Impressive Swedish Laboratories Dr. Arne Westgren honored us with a personally conducted tour of the Royal Academy of Sciences. In one of the stately chambers of this building, mem bers of the academy hold their delibera tions in selecting four of the five Nobel laureates. Another chamber houses the laboratory equipment, furniture, decorations, and mementos of Jons Jakob Berzelius. This is a priceless restoration of the spirit, times, and ac complishments of the great chemist. Any analyst, conscious of Berzelius' early contributions to analysis, has trepidation in signing the guest book. Dr. Westgren graciously conducted us to the Physics Department of the Nobel Institute, where much fundamental re search in nuclear physics is in progress.
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BECKMAN MODEL Β SPECTROPHOTOMETER A moderately priced precision in strument employing a glass-prism monochromator. Its low cost per mits the application of accurate, rapid spectropho to metric methods to r o u t i n e analyses f o r m e r l y a c c o m p l i s h e d by more t e d i o u s procedures. High photoelectric sensitivity is maintained over the wide spectral range of 3 2 0 to 1000 millimicrons.
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Analysis and Color Measurements . . . Techniques in General Organic and Inorganic Chemistry . . . Metals . . . Petroleum and Fuels . . . Glass, Plastics, Resins and Rubber . . . Biologicals and Medicine... Pharmaceuticals.. .Vitamins . . . Foods and Beverages . . . Oils, Fatty Acids and Pigments . . . Cosmetics . . . Clays, Paints and Papers . . . Textiles . . . Dyes and Leather . . . Plant Materials, Soils and Insecticides. • Special Sections include listings on Structural Identification . . . Rate and Equilibria Studies... Emission (Including Flame Spectrophotometry) . . . Special Instrumentation and Standards . .. Calibration Filters .. . Theory . . . and Miscellaneous References A free copy of this valuable bibliography will gladly be sent those supplying their job titles a n d the type of product or process in which they are working, together with name a n d address. Ask for Bulletin # 1 4 - 1 5
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The elegance and professional ap pearance of equipment in Swedish labora tories are striking, even though one is prepared for it from reading their publi cations. No one is startled to find cleanliness, order, and neatness in that country, but to an instrument-minded visitor it is apparent that the\ r do not approach apparatus or instrument de sign without full and constant coopera tion of skilled machinists, glassblowers, and artisans of every class. One would be foolish, indeed, to deprecate the "string-and-sealing-wax" approach to scientific investigation. Too much of our knowledge has come to us from those whose inspiration and genius overcame the limitations of the junk barrel. One gains the impression that our Swedish friends have no particular enthusiasm for gadgets. They prefer instruments, and with this attitude we have no quarrel whatsoever. The intense scientific and technical activity in Sweden and its highly de veloped instrument industry are star tling to the visitor. More than thirty agencies, institutes, and companies were represented in these exhibits, only a few of which we have described. We have completely neglected, for obvious reasons, the developments in communi cation. Some idea of the activity in that field can be inferred from the fact that there are nearly 6,000,000 tele phones in Sweden, where the total population is approximately that of New York City!
