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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
COLLECTIVE NUMERICAL PATENT INDEX to Volumes 31-40 of
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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)
