[Illustration: Fig. 44. SCHULTZE-TIEMAN APPARATUS.]
For the estimation of nitrogen in nitro-cellulose take .5 to .65 grm., and place in the decomposition flask f (Fig. 45), washing in with about 25 c.c. of water by alternately opening clips D and E. The air in the flask is driven out by boiling, whilst the air is shut off by the tube i dipping into the basin W, which is filled with the soda lye, and tube K is placed in the test tube R, which contains a few c.c. of water. As soon as all the air is completely driven out, clips D and E are closed, and the gas jet is taken away. (This flask must be a strong one, or it will burst.) Into test tube R, 25 c.c. of concentrated solution of protochloride of iron and 10 to 15 c.c. concentrated hydrochloric acid are poured, which are sucked up into the developing flask f by opening clip E, air being carefully kept from entering. The clip E is now closed, and tube i is put underneath the burette, and the development of NO gas is commenced by heating the contents of the flask f. When the pressure of the gas in the flask has become greater than the pressure of the atmosphere, the connecting tube begins to swell at i, whereupon clip D is opened, and the boiling continued with frequent shaking of the bulb, until no more nitrous gas bubbles rise up into the soda lye, the distilling over of the HCl causes a crackling noise, the clip D is closed, and E opened. The burette is again put hermetically on the indiarubber stopper in basin W, and the apparatus is left to cool until the water discharged through P shows the same temperature as the water flowing through (into the cooling jacket) Z. If the level of the soda solution in the tube X is now put on exactly the same level as that in the burette by lowering or elevating the tube X as required, the volume of NO obtained in c.c. can be read off within 1/10 c.c., and the percentage of nitrogen calculated by the usual formula.
[Illustration: FIG. 45.—Decomposition Flask for Schultze-Tieman Method.]
The solution of protochloride of iron is obtained by dissolving iron nails, &c., in concentrated HCl, the iron being in excess. When the development of hydrogen ceases, it is necessary to filter warm through a paper filter, and acidify filtrate with a few drops of HCl. The soda solution used has a sp. gr. of 1.210 to 1.260; equals 25° to 30° B. The nitro-cellulose is dried in quantities of 2 grms. at 70° C. during eight to ten hours, and then three hours in an exiccator over H_{2}SO_{4}. The results obtained with this apparatus are very accurate. The reaction is founded upon that of MM. Champion and Pellet's method.
~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:—
______________________________________________ | | | | | Total Nitrogen. | | Substances Analysed. |______________________| | | | | | | Calculated. | Found. | | |_____________|________| | | | | | Saltpetre (KNO_{3}) | 13.86 | 13.91 | | | | 13.82 | | | | 13.73 | | | | 13.96 | | Ammonium nitrate | 35.00 | 35.31 | | | | 34.90 | | | | 34.96 | | Barium nitrate | 10.72 | 10.67 | | | | 10.62 | | Nitro-glycerol | 18.50 | 18.45 | | Di-nitro-benzol[A] | 16.67 | 16.78 | | | | 16.57 | | Para-nitro-phenol | 10.07 | 10.03 | | Picric acid[A] | 18.34 | 18.42 | | | | 18.43 | | Ammonium picrate | 22.76 | 22.63 | | | | 22.67 | | Di-nitro-ortho-cresol | 14.14 | 14.10 | | | | 13.98 | | Tri-nitro-meta-cresol | 17.28 | 17.57 | | | | 17.27 | |_______________________|_____________|________|
[Footnote A: Dr. Bernard Dyer obtained 18.39 per cent. for picric acid and 16.54 per cent. for di-nitro-benzol.—Jour. Chem. Soc., Aug. 1895.]