J. W. Beams

The Production of High Rotational Speeds

Methods of spinning rotors to very high speeds by means of compressed air are discussed. A detailed description is given of the construction of apparatus to spin rotors both in gases at various pressures and in vacuum. Some uses of the apparatus and its operating characteristics are outlined.

Spinning Rotor Pressure Gauge

A magnetically suspended rotor pressure gauge is described for measuring pressures below 10−4 torr. The data are in good agreement with those obtained with a calibrated Alpert ionization gauge over the range 10−4 to 5×10−8 torr. When the gas in the vacuum system was frozen out with liquid helium, the rotor gauge recorded a residual pressure of about 5×10−10 torr. A brief discussion is given of a number of effects which unless eliminated may introduce errors into the measurements at the lowest pressures.

Magnetic Suspension for Small Rotors

A magnetic suspension for small rotors has been developed which employs scattered light to regulate the vertical height of the rotor. Upon entering a horizontal beam of light the rotor scatters or reflects light into a photo‐electron multiplier cell. This cell actuates an electronic circuit which in turn regulates the current through the supporting solenoid in such a way as to maintain the ferromagnetic rotor at the desired vertical position. Rotors with diameters down to 0.004″ have been stably supported. A 164′′ rotor was spun to an estimated speed of 800,000 r.p.s. which gave a centrifugal field in excess of one‐half billion times gravity. Besides providing a support for rotors, the apparatus may be used as an analytical balance for weighing materials inside a vacuum chamber. It detects changes in mass of from 10−8 to 10−9 gram. Other uses also are indicated.

Tensile Strengths of Liquid Argon, Helium, Nitrogen, and Oxygen

The tensile strengths of several liquids at low temperature were measured by a linear deceleration method. The values found were as follows (expressed in atoms): argon −12, nitrogen −10, oxygen −15, and helium −0.16. The values are somewhat lower than those calculated from the theory.

Magnetic Suspension Balance Method for Determining Densities and Partial Specific Volumes

Two modifications of the magnetic suspension balance are described for determining densities and partial specific volumes. Both modifications are capable of high precision. Also, they require comparatively small amounts of the materials and short times for the determinations.

Magnetic Suspension Balance

An analytical balance is described in which the materials to be weighed are attached to a ferromagnetic body that is freely suspended by the axial magnetic field of a solenoid. The vertical position of the suspended mass is maintained by the automatic regulation of the current through the solenoid by means of an electronic servo‐circuit actuated by a light beam and photomultiplier tube arrangement. The horizontal position of the supported mass is maintained by the symmetrically diverging field of the solenoid. Changes in the nonferromagnetic masses of the suspended bodies are determined by the resulting changes in the current through the solenoid necessary to keep the bodies freely suspended. Masses ranging from 105 grams to 2×10−6 gram have been suspended. The precision of the balance is limited only by the natural fluctuations in the circuit, the photomultipliers and the support system. This balance is especially useful where it is necessary to weigh materials inside of sealed chambers which contain gas...

Magnetic Densimeter‐Viscometer

A combination magnetic densimeter and viscometer, which essentially simultaneously measures the density and viscosity on 0.3 ml specimens of fluids, is described. A small cylindrical buoy is freely suspended magnetically and coaxially with a larger surrounding cylindrical glass tube which contains the fluid in which the buoy is completely immersed. After calibration, the electrical current in the air core solenoids which magnetically support the buoy measures the density of the fluid while the period of revolution at constant power input determines the viscosity. The density can be measured to the order of magnitude of one part in 106 and the viscosity to one part in 104.

Magnetically suspended vacuum-type ultracentrifuge.

A centrifuge rotor constructed of steel and Duralumin ST‐14 weighing 4.93 kilograms and having a radius of 65 mm to the center of the standard centrifuge cell, which contains the material to be centrifuged, is suspended magnetically in a high vacuum (pressure less than 10−5 mm Hg). The rotor is driven to running speed by an air turbine below the vacuum chamber. The turbine is connected to the rotor by a small steel shaft along the axis of rotation and passing through vacuum‐tight oil glands into the vacuum chamber. When the rotor reaches operating speed, the shaft is disconnected and the rotor is allowed to coast freely during the sedimentation experiment. This is possible because of the very small deceleration of the rotor (less than a 0.1 revolution per sec per hour). As a result the temperature and rotor speed not only can be measured accurately, but can be maintained very nearly constant. The ultracentrifuge has been used both for rates of sedimentation measurements and for sedimentation equilibrium m...

Spark Light Source of Short Duration

A simple spark-gap light source together with an associated pulsing circuit has been utilized to produce light flashes of approximately 10−7-sec. duration suitable for the study of shock waves produced by high speed bullets and for the photography of shock and turbulent disturbances in supersonic air streams.

An Inverted Air‐Driven Ultracentrifuge

An air‐driven ultracentrifuge is described in which the air turbine is below rather than above the large rotor or centrifuge. The centrifuge is mounted inside a vacuum tight chamber on a flexible shaft which extends vertically downward, through an oil gland that seals the vacuum chamber, to the turbine below the chamber. The rotating parts are supported upon an air cushion below the turbine. The turbine is driven by air jets. The rotation of the centrifuge is very smooth and the maximum speed is limited only by the strength of the centrifuge.