A simple photoelectric colorimeter

ORDINARY colorimetric methods of measurement suffer from the disadvantage of requiring subjective judgments depending on the colour sensitivity of the eye of the observer. Their accuracy is limited by the eye fatigue which they engender and is dependent upon the quality of the light by which they are made. Most of them are also subject to other limitations: they require the use of complex and empirical calibration curves, are relatively slow, or necessitate fairly large quantities of material. The improvements brought about by the use of spectroscopic or photometric methods are still limited by the basic disadvantage of subjective measurement, intensities of two fields having to be balanced against each other or spectral bands located. This paper describes a simple colorimeter, using a differential copper copper-oxide photoelectric cell and two colour filters, which possesses none of these disadvantages. It is relatively cheap, simple, and quick to use, can be adapted to very small quantities of fluid, and has a linear calibration curve. It is especially well adapted to the measurement of the degree of oxygenation of hwamoglokin solutions, and is not subject to the usual disadvantages of the other optical methods (such as inaccuracies due to inactive hsemoglobin) which have been used for this purpose.