The authors communicate the following:

We previously reported on the making of the light absorbance measurements using the CHEMPAC (Manufactured by E&L Instruments, 70 Fulton Terrace, New Haven, CT 06512; purchased from Electronic Marketing Co., 1092 Johnson Road, Woodbridge, CT 06525.) laboratory/computer interfacing colorimeter. Reasonable results were obtained using the GREEN and YELLOW sensors; however, anomalous results were obtained using the RED sensor.

The problem with our previous measurements using the RED sensor has been traced to the placement of the RED sensor high up in the colorimeter sample compartment coupled with our apparent incomplete filling of the sample cuvette in making the light absorbance measurements.

The problems we noted in the original article have been eliminated by attention to the complete filling of sample cuvettes in making both calibration and absorbance measurements. The RED sensor gives results comparable in both precision and accuracy to those obtained using the GREEN and YELLOW sensors. The correct data may be obtained by writing the authors at: Department of Chemistry, Worcester Polytechnic Institute, Worcester, MA 01609.