VOLUME 2 8, NO. 4, APRIL 1956 459 acteristio lines to be counted, and absorption effects in three regions to consider. The three counts should, however, contain enough information in many cases to permit the drawing of valid conclusions.

The differential method of colorimetric analysis as applied to the Beckman Model DU spectrophotometer is discussed. The maximum increases in accuracy of this method over the normal one are computed for the instrument.Taking special precautions, experimental accuracies and precisions in the range of about ±0.5 to ±1 part per thousand are obtained on potassium dichromate and potassium permanganate solutions.

A rapid and accurate method for determining nitrate in alkaline earth carbonate mixtures used as cathode coating materials in the electronics industry utilizes ultraviolet absorption of nitrate ion in dilute perchloric acid solution. The system is sensitive and stable and adheres to the usual absorption laws. The interference of a number of anions and cations is considered. Because of the high purity of the carbonates with respect to metal ions, no separations or corrections need ordinarily be employed.However, methods for dealing with the interference of common metal ions are considered with a view toward possible wider application of the method.

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