For routine quantitative spectrographic analysis of phosphorus, using the line at 2136A, the Geiger-Müller photoelectron counter has certain advantages over both the photographic plate and the electron multiplier photo-tube. The construction of the counters and the methods of electrically shielding and mounting them on the Littrow spectrograph are briefly described. The adjustments of counter orientation, slit widths, and focus are discussed with reference to the analyses of ferrous alloys where good resolution is necessary. Because of the absorption of radiation by quartz at low wave-lengths, both absolute and relative intensities are dependent upon the position of the arc on the electrode surface. This effect, which results in appreciable error in the measured percentage composition of a sample, is investigated photographically and with G-M counters, and several methods of reducing the effect are discussed. The effect of temperature changes of the dispersing prism on line position is investigated and a suitable method of control is mentioned. Preliminary consideration of this direct-reading method shows that it seems possible to reduce the various errors so that the source fluctuation is the controlling factor.
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