LECTURE EXPERIMENT ON THE SYNTHESIS AND COMBUSTION OF AMMONIA F. FROMM Polytechnic Institute of Puerto Rico, Son Gerrnirn, Puerto Rico
THE production of nitric acid by the arc process is a very common lecture experiment. But as the commercial production of nitric acid is now based on the oxidation of ammonia, i t is desirable to show also the synthesis and combustion of ammonia in a lecture demonstration. It seems that such an experiment has not been described in the Anglo-American literature (1); hence, it may be worth while to give an account of the method used more than ten years ago in the Departmeut of Technology a t Konigsberg (2). For the synthesis of ammonia from the elements any source of hydrogen and nitrogen may be used. As the yield is not important, high pressure can be avoided, provided that a good tungsten catalyst is prepared. Following Franck's suggestions (3), 10 g. of purified, fibrous asbestos is soaked in a solution of 10 g. of tungstic acid in ammonia and evaporated to dryness. The dry asbestos is then heated to 600°C. in a hard glass tube in a current of dry ammonia gas, until the tungstate is reduced and the asbestos appears black. The catalyst is then cooled in a current of ammonia, and finally hydrogen gas is passed over it until ammonia can no longer be detected by the test with turmeric paper. This catalyst is placed in a pyrex glass combustion tube supported horizontally and connected by a Ttube with two gas washing bottles and sources of hydrogen and nitrogen. The speed of the two gases through the wash bottles is regulated so that three bubbles of hydrogen enter the tube with one bubble of nitrogen. The issuing gases are led into an Erlenmeyer flask or other suitable receiver. As soon as the tube is free from any explosive mixture with air the catalyst is
heated gently. After a short time the formation of ammonia can be shown in the receiver by the test with turmeric paper or the formation of white fumes of ammonium chloride. For the combustion of ammonia the same apparatus may be used. The tungsten catalyst is replaced by platinized asbestos or platinum gauze. Ammonia gas and a mixture of two volumes of air and one volume of oxygen are passed a t the same speed through the tube. The receiver contains a little water. As soon as the catalyst is heated to 400°C. i t begins to glow without further heating and the formation of nitrous gases takes place. They dissolve readily in the water of the receiver where the presence of nitric acid can be shown by the usual tests. Sometimes it happens that white fumes of ammonium nitrite are formed instead of the brown nitrogen dioxide. This is due to an excess of ammonia. In order to avoid this it is only necessary to reduce the quantity of ammonia passing through the tube. In this form the oxidation of ammonia is less dangerous than the test tube experiment suggested by H. F. Davison (4). Moreover, it offers the advantage that the reaction is not stopped a t the production of the nitrogen oxides, but is continued to the actual formation of nitric acid. LITERATURE CITED
J. CHEM. EDUC., 446 (l941). (2) HESSENLAND, "Prakt~kumder gewerblichen Chemie," J. F. Lehmann's Verlag, Miinchen, Berlin, 1938, pp. 61-2,66-7. (3) Cf. ARENDT-DURMER, "Technik der Experimentalchemie," Verlag Leopold Voss. Leipzig, 1925, p. 512. (4) DAVISON,"A collection of chemical lecture experiments," Chemical Catalog Company, New York City, 1926,". 55.
