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Hot wires of various design, operated by the constant resistance method, were calibrated by means of a plane sound wave of 2500 Hz. This is achieved by locating a small open resonance tube axially in a homogeneous incompressible airflow. Its third harmonic is excitated by superimposing a coaxial, damped, progressive, plane wave on the main airstream. The hot wire to be calibrated is situated in an anti-node of the particle velocity. The amplitude at this station is known from the pressure gradient of the standing wave measured at two small holes in the wall by a probe microphone. This device in turn is calibrated in a specially developed “pistonphone”. Numerical results of the diverse designs are communicated; an absolute accuracy of ±2% is achieved.

A theoretical and experimental investigation is made of supersonic ejectors with mixing at constant cross-section. In the theoretical part formulae are derived treating the essential points of the behaviour of such an ejector. The theory is mainly based upon one-dimensional flow of a perfect gas; some extensions are included concerning the influence of friction and mixing profile.

Measuring a fluctuating pressure at a discrete point in an air flow requires a narrow probe connected by a transmission tube (of arbitrary length) to the membrane chamber of a microphone. A correct transmission of the pressure in the tube is achieved by a special construction of the chamber giving the tube the characteristic specific acoustic impedance at its terminal. The chamber is accordingly shunted to the ambient atmosphere by a narrow slit; the effect of the inertia of the slit is balanced by the capacity of the chamber, the resistance constitutes the required real impedance.

Es ist eine Methode für die Messung eines schwankenden Staudruckes entwickelt worden. Das Gerät besteht aus Staurohr, Verbindungsrohr, piezo-elektrischem Druckaufnehmer und elektrischem Filter. Die aerodynamischen, mechanischen und elektrischen Eigenschaften des Systems werden besprochen und eine Eichmethode beschrieben. Das ausgeführte Gerät besitzt eine nahezu geradlinige Eichkurve bis 800 Hz und eignet sich für die Turbulenzmessungen hinter verschiedenen Gittern. Die Ergebnisse stimmen befriedigend mit Hitzdrahtmessungen überein.

A search for high molecular residues in penicillin G was carried out using several recently described methods. By the membrane filtration method the protein content of a large number of batches of penicillin G, 6-APA (chemically prepared), and ampicillin was determined. Significantly lower protein values were found for these compounds than for microbiologically produced 6-APA and the ampicillin made from it. Purified macromolecular complexes of penicillin gave protein values in the membrane filter method. Our results indicate that the protein content of most commercially available benzylpenicillins is negligible.

The aim of the investigation was primarily the computation of the dynamical corrections on the static calibration curve. A brief account is given of the available analytical expressions for the heat transfer of a hot wire to the ambient airflow. The appropriate form is inserted in the small perturbation energy equation giving, with constant values of the characteristic parameters, a linear second order differential equation. A number of numerical examples was computed from the exact solution yielding the influence of frequency on the sensitivity and the temperature distribution along the wire. The analysis is supplemented by a short review of some complicating factors not included in the linear theory.

A harmonic pressure generator is developed based on the principle of plane sound waves. The pressure is generated in a cylindrical enclosure by a piston with a flat bottom; the piston is driven by a coil situated in a radial magnetic field. The coil is supplied with an alternating current; the corresponding amplitudes of the piston are measured by a precision accelerometer mounted inside the hollow piston.