Volume 13, Issue 10, October 1942
Index of content:
13(1942); http://dx.doi.org/10.1063/1.1769938View Description Hide Description
An apparatus is described for following in detail changes in light intensity that occur in times of the order of one microsecond. It has been applied to measure the decay of fluorescence and to measure the decay of light from a nitrogen discharge. The light to be measured falls on an electron multiplier tube which is connected to a cathode‐ray oscilloscope, on which the decay curves and a time scale are observed. In measuring fluorescence, a ``square'' pulse of exciting light is produced by a Kerr cell whose potential difference is controlled by the sweep circuit of the oscilloscope. For the fluorescence of diacetyl vapor a mean lifetime of 1.40×10−3 sec. was obtained, for diacetyl dissolved in water and in CS2 1.0×10−6 sec. and 1.9×10−6 sec., respectively. With the nitrogen discharge tube in place of the Kerr cell, photographs were taken at several pressures of the decay of the light of red and blue band systems, and of the discharge tube current which decreases more rapidly than the light. The blue system (C 3Π→B 3Π) decays exponentially with a mean lifetime (extrapolated to zero pressure) of 7.7×10−6 sec. The red system (B 3Π→A 3Σ) decay can be resolved into two exponentials with mean lifetimes of 29×10−6 sec. and about 1.5×10−6 sec., respectively.
13(1942); http://dx.doi.org/10.1063/1.1769939View Description Hide Description
An apparatus is described for the measurement of the scattering of low velocity ions in gases. This consists essentially of an ion source, focusing devices, a magnet for velocity and species selection, and a measuring chamber. Technique of construction and operation is described which enables scattering curves to be obtained where the effective cross‐sectional area is plotted against ion velocity down to a velocity of two volts. This apparatus has been found useful for condensable gases such as water, as well as for non‐condensable gases. It has been constructed in such a way that ion neutralization as well as elasticscattering can be quantitatively determined as a function of velocity.
13(1942); http://dx.doi.org/10.1063/1.1769940View Description Hide Description
Previous cells for the ultracentrifuge have proved inadequate because of leakage, distortion, breakage of quartz windows, and lack of facilities for proper alignment. These difficulties have been studied and remedies provided, particularly through the strengthening of cell parts, the use of a specially coated Duralumin centerpiece, the provision of a key for alignment, and an arrangement for always orienting the windows in the same manner to prevent reversal of stresses.
- PHYSICAL INSTRUMENTS FOR THE BIOLOGIST
The Oximeter, an Instrument for Measuring Continuously the Oxygen Saturation of Arterial Blood in Man13(1942); http://dx.doi.org/10.1063/1.1769941View Description Hide Description
The oxygen saturation of arterial blood in man can be measured continuously in situ by means of bichromatic photoelectric colorimetry of the intact fully flushed ear. The accuracy of the device as determined by gas analysis of arterial blood samples is from 3 to 8 percent. The entire optical and photoelectric system, comprising a miniature lamp bulb, two color filters, and two selenium barrier‐layer photo‐cells, weighs 30 grams, and slips over the shell of the ear. One of the color filters transmits a wave‐length band which is equally absorbed by oxy‐ and reduced hemoglobin, thus providing a means of measuring the amount of total hemoglobin in the optical path, independent of its degree of oxygen saturation. The other color is very differently absorbed by the two hemoglobin forms. Several direct reading forms of the instrument are discussed.