REACTIONS AND IDENTIFICATION 323 with dilute sulphuric acid. A greenish-blue coloration, some-times followed slowly by an actual precipitation of Prussian blue, indicates nitrogen. If only a green coloration is obtained, it often indicates insufficient reaction with the sodium: if, however, such a solution is filtered, "specks 1 ' of deep blue material can fre-quently be seen collected on the filter-paper and are a clear indication of the presence of nitrogen. (1) Some nitrogenous organic compounds react very slowly with sodium even under the above conditions of fusion, and give in conse-quence only a feeble indication for nitrogen. If, in spite of this feeble indication, the general properties of the substance point to the presence of nitrogen, repeat the fusion using the apparatus shown in Fig. 69, but heat the sodium until it boils gently in the vertical tube. Then drop the substance, in very small portions at a time, down the tube, so that it falls through the column of sodium vapour into the boiling metal. Nitrogen
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