The design and construction of a photoelectric spectrophotometer for analytical research
A spectrophotometer has been built, consisting of three parts, a monochromator, a photocell amplifier, and a recorder;The monochromator used a new optical system, a modification of the Wadsworth mounting for concave reflection diffraction gratings;Upon calibration of the monochromator using a helium spectrum tube as a light source, the wave length scale was found to be linear;Seven separate amplifiers were constructed, of which one was finally used. It suffered less from random currents and drift than did the other six, but was still so erratic that results could be reproduced with a precision of only five percent;A recorder mechanism was constructed, and was found to be too unreliable for good analytical work even after a number of changes were made in the circuit;The transmittancies were obtained for two glass filters calibrated by the Bureau of Standards. These were found to check reasonably well with the calibrated values, except at the extreme ends of the spectrum. This comparison afforded a qualitative estimation of the amount of stray light present in the monochromator. A barrier layer cell coupled directly to a galvanometer was used in these determinations;Results of high precision were found to be not obtainable in the instrument constructed without the use of optical and electrical parts of precision manufacture.
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