Photoelectric Colorimetry in Microanalysis

Abstract

Photoelectric methods afford precise means for investigating colorimetric reactions. Most of the methods are in the range of microanalysis. The highest precision is undoubtedly afforded by the vacuum photoelectric cell-amplifier method. Barrier-layer cells are precise but considerably simpler. Either method can be made to yield data of fundamental importance.light Jo incident on both cups, containing solutions of concen-

Colorimetric Determination of Copper with Ammonia

“…Conformity to Beer's Law That Beer's law is followed by the color system is shown by the fact that a straight line resulted when the logarithms of the observed transmittancies at 620 µ for six solutions, containing from 40 to 600 p. p. m. of copper, were plotted against the respective concentrations. This is in agreement with the work of other investigators (16,26,27).…”

Photoelectric Colorimetry

“…That the fundamental law of light absorption, the Lambert-Beer relationship, should form the basis for every exact colorimetric method has been shown by Müller (6). In this investigation the conformity of the absorbing entity to this relationship was used as the criterion of an acceptable method.…”

“…Two photoelectric colorimeters were used in this work, both of which have been described previously (6,7). Preliminary measurements were made using the photronic cell instrument, by the use of which a photometric precision of 0.5 to 1 per cent is obtained.…”

Spectroscopic Determination of Copper in Ores and Mattes

“…With the development of photoelectric colorimeters it is now possible to dispense with the use of standard solutions. About 2 years ago such an instrument called the photelometer was devised by Sanford, Sheard, and Osterberg (7) and recently similar instruments have been described by Eimer and Amend (1), by Yoe and Grumpier (9), by Zinzadze (10), and by Mtiller (6). In using them the intensity of light transmitted by a colored solution is correlated with the concentration of the constituent responsible for the color.…”

“…Since Beer's law has been shown (6,9) to hold for ammoniacal copper solutions up to concentrations of almost 1 gram of copper per liter, the concentration of copper in a given solution can be calculated from the fundamental Lambert-Beer equation I = 7o X 10-ric in which 7o represents the intensity of the incident light of given wave length which enters the solution, I the intensity remaining after its passage through the solution, l the length in centimeters of the solution, c the moles of absorbing substance per liter of solution, and e a constant which is a measure of the absorption due to a single molecule and is called the molecular extinction coefficient.…”