LETTERS To the Editor: In the account of the simple demonstration of the oxidation of ammonia given by Hauben & Siegel in your April issue, it was noted that none of the previously described demonstrations show how one can take advantage of the exothermic nature of the reaction. A very simple method of demonstrating the same process is in use in this laboratory, and was obtained from Professor E. J. Hartung of the University of Melbourne. The catalyst consists of a helm of stout platinum wire that is mounted in the end of a piece of soft glass tubing, the tubing is fitted with a flat cork so that when the helix is introduced into a conical flask of about 1-liter capacity the cork rests loosely on the mouth of the flask, and the helix is suspended about 4 to 5 cm. above the bottom of tbefiask. In order to demonstrate the reaction a few cc. of
concentrated ammonia solution (density 0.880) are poured into the flask. The platinum wire helix is then heated to bright redness in a Bunsen flame, and while still hot is lowered into the flask. The ammonia mixed with the air of the flask begins to he oxidized a t the surface of the catalyst, and within about a minute the flask is full of a fine cloud of crystals of ammonium nitrate. The exothermic nature of the reaction is very obvious from the continued glowing of the catalyst which is still visible, even when a suitable amount of ammonium nitrate fog has been formed. We have always found this demonstration to be very simple in operation, and to be quite spectacular. I t has never been found necessary to treat the platinum wire specially other than to be sure that it is cleaned. N. S. BAYLISS
PHASE DIAGRAMS AND THE MASS LAW (Continued from page 487) ACKNOrnEDGMENT
data which are available in the published literature (Gf. I , 2). If one wishes to consider the probable form to Of these high-tem~erature diagrams high pressures, one should take account of the fact that ammonium carbamate has a solid-liquid-vapor triple point a t approximately 152'C. and 83 atm. @). The compound also becomes chemically unstable a t high temperatures.
The present article has been written largely as a sequel to the paper of Briggs Migrdichian the ammonium carhamate equilibriuni and, in closing, the author hereby acknowledges it as such, LITERATURE CITED
(1) Bruccsnm MI~RDIC~IAN, J. Phw. Chem., 28, 1121 (1924).
ti)
(1929).
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Sot,. 51, 748
