~The Kjeldahl Method of Determining Nitrogen.~--This method, which has been so largely used by analysts for the determination of nitrogen in organic bodies, more especially perhaps in manures, was proposed by J. Kjeldahl,[A] of the Carlsberg Laboratory of Copenhagen. It was afterwards modified by Jodlbauer, of Munich,[B] and applied to the analysis of nitro- explosives by M. Chenel, of the Laboratoire Centrale des Poudres, whose method of procedure is as follows:--0.5 grm. of the finely powdered substance is digested in the cold with a solution of 1.2 grm. of phenol and 0.4 grm. phosphoric anhydride in 30 c.c. of sulphuric acid. The mixture is kept well shaken until the solution is complete. From 3 to 4 grms. of zinc-dust is then cautiously and gradually added, the temperature of the mass being kept down until complete reduction has been effected. Finally, 0.7 grm. of mercury is added, and the process continued in the usual way, according to Kjeldahl; that is, the liquid is distilled until all the ammonia has passed over, and is absorbed in the standard acid. The distillate is then titrated with standard ammonia. [Footnote A: J. Kjeldahl, _Zeitschrift Anal. Chem._, 1883, xxii., p. 366.] [Footnote B: Jodlbauer, _Chemisches Centralblatt_, 1886, pp. 434-484. See also _Arms and Explosives_, 1893, p. 87.] The NO_{2} group is at the moment of solution fixed upon the phenol with the production of mono-nitro-phenol, which is afterwards reduced by the action of the zinc-dust into the amido derivative. During the subsequent combustion, the nitrogen of the amido-phenol becomes fixed in the state of ammonia. M. Chenel is perfectly satisfied with the results obtained, but he points out that the success of the operation depends upon the complete conversion of the phenol into the mono-nitro derivatives. This takes place whenever the organic compound forms a _clear solution_ in the cold sulphuric acid mixture. Substances like collodion or gun-cotton must be very finely divided for successful treatment. The following table shows some of the results obtained by M. Chenel:--