Oklahoma Agricultural and Mechanical College, Stillwater, Oklahoma
THE following procedure is suggested as a couvenient one for conducting the digestion of samples in the Kjeldahl method for nitrogen when the usual digestion rack is not available, or for some reason cannot conveniently he used. The method has been tried out by students in the regular course in quantitative analysis, working in a crowded laboratory, and functions perfectly. Prepare the sample for digestion in the usual manner. Select an ordinary Gooch filtering crucible of such size as to fit nicely in the mouth of the flask. Line the mouth of the flask with a gasket made of lead or tin foil, to provide a tight fit of the crucible in the mouth of the flask. With the crucible snugly in place, fill it about two-thirds full with medium or coarse fiber
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asbestos, loosely placed. the asbestos with concentrated sulfuric acid and proceed with the digestion. The choking acid fumes, copiously produced, are perfectly absorbed in the crucible, no hood or special equipment being necessary. To shorten the time required for digestion of the sample, the use of some form of selenium catalyst is recommended. Of these, cupric selenite appears to be the most effective. For details concerning the use of this substance as a catalyst in the Kjeldahl method for nitrogen, see the Journal of Biological Chemistry, 113, (3), April, 1936. The preparation of cupric selenite is described in the Journal of the American Chemical Society, 52, 3881 (1930).
