Guy Barr

Two designs of flow-meter, and a method of calibration

A compact form of capillary-tube flow-meter is obtained by enclosing the capillary in the widened arm of a U-tube manometer. A modification of Becketts pulsing gas meter is described, in which a stream of gas displaces liquid from an inner to an outer tube; when a certain pressure-difference is reached, the breaking of a liquid seal allows the gas in the inner tube to be discharged so that the original conditions are restored. The volume discharged per pulse from such a meter was found to be 10 per cent. greater at high speeds than at low. Calibration of meters of small capacity is effected by connecting them to a graduated tube that has a soap film across its bore. When the walls of this tube are wet, the film is mobile and stable, so that gas may be collected and measured at a pressure that is almost exactly atmospheric.

Errors in viscometry due to surface tension

In viscometers of the Ostwald type used for the determination of kinematic viscosities relative to water, surface tension causes a reduction of the head available and increases the time of flow. The correction is greater for water than for organic liquids, but is not proportional to the surface tension. Earlier estimates of the correction are shown to be suspect, and the classical tables of Bashforth and Adams are applied to show how the capillary rise in a measuring bulb of specified size (3.85 ml.) and form varies during the discharge. The calculated corrections for two liquids with surface tensions differing rather more than those of water and benzol diverge by 0.5% when a mean head of 10 cm. is assumed, and a simple experiment demonstrates that this estimate is probably low owing to effects of drainage on the shape of the meniscus. Two methods are proposed for eliminating the correction during the calibration of viscometers.

A motor-driven circulating pump

The pump is suitable for circulating gas rapidly at pressures not far from atmospheric, through a system of low resistance. A glass bell is enclosed in a vessel, which may be entirely of glass, containing mercury into which the bell dips: the spaces above and below the bell communicate with two pairs of valves of improved type. The bell is raised and lowered mechanically, pumping gas on both strokes.

A New Relay for Moderately Heavy Currents

The action of the relay depends on the fact that no arc can be maintained between mercury electrodes in hydrogen. One lead is brought to mercury contained in a vertical tube within a solenoid. An iron rod, at the upper end of which is a glass cup, floats in the mercury. The cup also contains mercury, and the other lead is connected to an iron rod which dips into this. When no current flows in the solenoid, the rim of the cup is about 1 cm. above the level of the main body of mercury. When the relay current (about 0.03 ampere) is running the iron rod is sucked down until the rim of the cup is submerged by about 0.5 cm. The space above the mercury contains hydrogen. The relay can be used to break quite large currents (20 amperes) without much spark.

The construction of wave-length scales for spectrograms

A method is described by which an approximate scale of wave-lengths may be projected geometrically from a uniformly divided scale on to a spectrogram whereon a sufficient number of lines have been identified to enable constants of a Hartmann interpolation formula to be derived. Such a scale is of value in assisting the recognition of other lines between which accurate interpolation may be required.

Two new methods of measuring the internal diameters of transparent tubes

Two new methods of measuring the internal diameters of glass and other transparent tubes are described. The first consists in immersing the tube to be tested in a suitable liquid and varying the wave length of the illuminating beam until equality of refractive index is obtained. The system being now homogeneous, the diameter can be measured directly. Information is given with regard to the most suitable liquids to employ and the paper contains a number of practical hints which will facilitate the carrying out of the test. The second method consists in taking an X-ray shadow photograph of the tube and measuring the dimensions of the image formed. Between the two methods it is possible to measure accurately the internal diameter of practically any type of transparent tube, whether sealed or open, no matter what the outside shape of the tube may be.