°Average values, using calibration curve prepared in absence of U.region of 1 Mg. of technetium. However, this blank, if not corrected for, nullifies a negative error at higher technetium levels, which is probably due to oxidation of the technetium (V) thiocyanate. Consequently, reasonably accurate results are obtained in the presence of a limited amount of nitrate.Above 6% nitrate, the thiocyanate in the extract deteriorates too rapidly to permit accurate measurement of absorb-