Selenium as a catalyst in the Kjeldahl method as applied to soil and grass analysis

Abstract

(a) A comparison was made between the catalytic efficiency of selenium and of copper sulphate in the Kjeldahl method as applied to the analysis of grass. The same value for total nitrogen was eventually obtained by both methods, but with selenium it was reached some 90 min. earlier than with copper sulphate.(b) The clearing of the digested matter was no criterion for deciding whether all the nitrogen in grass had been converted to ammonium sulphate, maximum values not being obtained with selenium until between 2 and 3 hours afterwards.(c) The catalysts were compared for three samples of soil with digestion periods ranging from when the digested material first cleared to 32 hours afterwards. The selenium figures showed an increase for the first 3 hours, and then remained constant up to the 32-hour period. The copper sulphate figures, however, showed a steady increase for the first 24 hours, after which they became constant at the same values as those reached earlier by the selenium figures.