An automatic recording spectrophotometer designed to cover the range 10,000 to 2000A is described. With present light sources the instrument will trace absorption curves at high speed from 9800A to 3400A, and can be used somewhat more slowly to cover the spectrum to 2300A. A ten-foot concave grating monochromator with fixed slits is used to provide a spectral band 0.5 to 10A wide, the purity available depending on the light intensity and the speed of recording desired. An 11-stage electron multiplier is used to balance a light beam which has passed through the sample to be measured, against the same beam later reduced by a photometric disk by a recorded amount. An electric “memory” device is used to accomplish this balance, and at the instant of balance a spark is passed through a piece of suitable graph paper wrapped around a rotating cylinder. Twenty absorption measurements can thus be made and recorded per second. The instrument will plot either transmission or density values against wave-lengths on a linear scale, to an accuracy of about 1 percent.
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