Determination of Total Nitrogen, Nitrate-Nitrogen, and Total Nitrogen not Including Nitrate-Nitrogen: Further Observations on a Modification of the Official Salicylic-Thiosulphate Method

Abstract

The data here presented are in continuation of a series of investigations previously reported (Ranker, '25). These previous data were presented in support of a proposed modification of the official salicylic-thiosulphate method for the determination of total nitrogen including nitrate-nitrogen. BThe recommended procedure is as follows: Place the sample in an 800-cc. Kjeldahl flask; adjust to neutrality or make slightly alkaline; if water is present evaporate just to dryness on a water bath under vacuum. Add 35-40 cc. of salicylic acid mixture (1.0 gm. of salicylic acid to 30 cc. of concentrated nitrogenfree sulphuric acid); mix thoroughly and allow to stand for at least an hour with occasional shaking (if organic matter is present, stopper tightly with a rubber cork and allow to stand over night). Add 5 gms. of sodium thiosulphate and heat for 5 minutes with a low flame; cool; add 7-10 gms. of anhydrous sodium sulphate and a pinch of copper sulphate. Digest for an hour at the boiling point after the solution clears; just before the solution solidifies dilute to an estimated volume of 400 cc.; cool completely. Add a small piece of paraffin, 100 cc. of a saturated solution of sodium hydroxide, and a piece of