The Design of a Precision Photoelectric Colorimeter

Abstract

AMONGthe first applications of the modern photoelectric cell was its use to replace the human eye in photometric measurements. Many circuits and cell arrangements for specialized types of photoelectric photometry have been proposed in the literature (4, 8, IS, 17). The earlier photometers were of the direct-reading type and employed a single photoelectric cell. In 1919, Gibson (8) of the Bureau of Standards described the null method for photometric measurements, using it for the routine photometry of lamps. The null method with two photoelectric cells eliminates many of the inaccuracies entering through direct reading.More recently the photoelectric cell has received attention as a means of minimizing the human element as a factor in colorimetry. Müller (11) in 1928 described a photoelectric colorimeter of the direct-reading type and discussed its ap-

Determining Riboflavin in Dried Milk Products

“…By the proper selection of filters, the photometer may be used for many types of colorimetric measurements. One of the limitations in the use of filters instead of a monochromator is that strict proportionality between concentration and density (log Iq/I) is obtained only over a limited range of concentrations, if the transmission curve of the filter does not exactly coincide with the absorption band of the pigment (8). Consequently, if the photometer itself does not give a linear response to varying light intensities, a calibration curve must be plotted for each pigment.…”

Modified Photoelectric Photometer for Colorimetric Determinations in Water and Sewage Laboratories

“…Three photoelectric circuits have been built. A is the unbalanced simple type described by Hurwitz (3) which was built for $26, B is the balanced series photronic cell circuit described by Brice (#), and C is the balanced parallel photronic cell circuit described by Winthrop, Shrewsbury, and Kraybill (9). Circuits B and C are twice as expensive to build but have the distinct advantage of being independent of changes in light intensity due to voltage fluctuations when laboratory heating units or automatic pumps go on or off the power circuit.…”

A multipurpose photoelectric reflectometer

“…In many instances, however, an abridged spectrophotometric measure-613 ment is useful because it is known that some particular property may be studied by using a single spectral range or several ranges each isolated by spectral filters. One or two wavelength regions are most commonly found to be sufficient for chemical analysis by photometric means ("chemical colorimetry") [10,52,58].…”