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A Turbidimetric Potassium Determination Affected Little by Temperature¹

ABSTRACT

A modification of the turbidimetric cobaltinitrite method for determining potassium is presented. The method is applicable to use in routine soil testing laboratories and has been in use for 3 years in Kansas county laboratories.

The method is not appreciably affected by temperature changes over the temperature range of 15° to 35° C but is subject to errors at temperatures greater than this. Comparisons of the effect of temperature on this method with two methods now in common use showed it to be subject to less error.

The effects of temperature have been minimized by modifying the usual techniques in two ways: (1) by selecting the proper wave length and adjusting the photometer with a blank solution to prevent measurement of the amount of color in the solution phase, and (2) by introducing sodium cobaltinitrite powder directly into the potassium solution-alcohol mixture, resulting in slow formation of the potassium precipitate.

¹ Contribution No. 477, Department of Agronomy, Kansas Agricultural Experiment Station, Manhattan, Kans. Presented before Division II, Soil Science Society of America, Cincinnati, Ohio, November 18, 1952.

Received for publication December 26, 1952.