Year: 1935
Type: article
Abstract: ABSENCE OF NITRATES.-Any of the recognized modifications of the Kjeldahl method may be used.The amounts of catalyst and acid required vary with the amount of organic matter to be oxidized.For 50-cc.aliquots of the alcoholic extract of fruit spurs, containing 1-3 mg.N, 15 cc.concentrated H2SO4 and 5-7 gm. of a mixture of 10 gm.K2SO and 1 gm.CuSO4 * 5H20 were adequate.Frothing is likely to be severe as the last of the water or alcohol is driven off.By careful regulation of the flames and occasional shaking it has been possible to make 30 digestions at once without loss.For the final titration the mixed methyl red-methylene blue indicator proposed by JOHNSON and GREEN (8) is excellent.B. IN THE PRESENCE OF NITRATES.-Theuse of the salicylic acid method devised by RANKER and described in the previous report ( 27) is trouble- some because of the necessity of evaporating an exactly neutral portion of the extract to dryness in the Kjeldahl flask before adding the reagents.This difficulty is overcome by the reduced iron method, which was adapted to plant materials by PUCHER, LEAVENWORTH, and VICKERY (11).The reduction may be carried out in either aqueous or alcoholic solution.The conditions for the reduction prescribed by PUCHER et al. should be followed exactly.Those for the subsequent digestion may be modified somewhat.For 25-cc.aliquots of the alcoholic extract of tomato leaves, containing 1-5
Source: PLANT PHYSIOLOGY
DOI: 10.1104/pp.10.2.393
Language: English
Subfield: Soil Science
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W4230456402