Theoretical organic chemistry / by Julius B. Cohen.

  • Julius B. Cohen
Date:
1902
Catalogue details

Licence: Public Domain Mark

Credit: Theoretical organic chemistry / by Julius B. Cohen. Source: Wellcome Collection.

    40/604 (page 20)
    apparatus. In this case, fused lead chromate broken up into small pieces must be used in place of the 'copper oxide in the combustion tube. The halogens and sulphur are retained by the lead, the former as halide salt, and the fatter as lead sulphate. Nitrogen.—Nitrogen is usually estimated by one of the fol¬ lowing methods : by burning the substance with copper oxide in an atmosphere of carbon dioxide, and collecting the free nitrogen over potash solution (Dumas) ; by heating the sub¬ stance with soda-lime, and estimating the ammonia evolved (Will and Varrentrapp) ; or by decomposing the substance with concentrated sulphuric acid at a high temperature, and con¬ verting the nitrogen into ammonium sulphate (Kjeldahl). Whilst Dumas’ method is universally applicable, the other two pro¬ cesses cannot always be employed, and only give trustworthy results when the nitrogen in the compound is directly combined with carbon and hydrogen. Dumas’ Method.—A combustion tube closed at one end is filled as shown in Fig. 15. A layer of magnesite is first intro¬ duced, then some coarse copper oxide. This is followed by Fine COARSE spiral Coarse CuO cuO CuO magnesite III iVS S' <■ 15cm. < 13cm. *8cm.V 13cm. v ASBESTOS ASBESTOS . PLUG _ PLUS Fig. 15.—Arrangement of tube for nitrogen estimations. the substance well mixed with fine copper oxide. The tube is then partly filled with coarse copper oxide, and finally a spiral of metallic copper is introduced. The copper spiral serves to reduce any oxides of nitrogen, which would be otherwise absorbed by the potash solution. The open end of the tube is attached to a Schiffs azotometer (Fig. 16). It consists of a graduated tube, surmounted with a tap and furnished with two side tubes, one being attached to the combustion tube, and the other to a reservoir containing potash solution. By opening the tap and raising or lowering the reservoir, the solution may be introduced into the graduated tube or removed into the reservoir. The reservoir is first lowered, and the potash solution run out of the