116 Dr. E. P. Perrnan and Mr. G. A. S. Atkinson. [May 3, 



very nearly so. These results indicate that at the highest temperatures 

 the decomposition is of the first order, i.e., it is monomolecular, pro- 

 ceeding according to the equation NH 3 = N + 3H ; the union of the 

 atoms to form molecules is probably so quick that it can be neglected 

 when compared with the rate of decomposition of the ammonia 

 molecule. The departure from this mode of decomposition at lower 

 temperatures is possibly caused by the volume and mutual attraction of 

 the molecules. No formula has yet been devised to express the results 

 satisfactorily. 



In the presence of substances having a catalytic action, the resulting 

 curve is altered in character, the curvature being greater at the higher 

 pressures. This is well shown in the curves at 750 and 791 (fig. 2), 

 mercury vapour being present, and in those at 797 and 1025 (fig. 3), 

 when iron wire and platinum black respectively were present. In 

 these two latter experiments it will be noticed that the rates of 

 decomposition reached and passed those without catalyser for about 

 100 higher. 



Eject of Sudden Change of Pressure on the Rate of Decomposition. 



As a final experiment the effect of a sudden change of pressure was 

 tried, the globe containing both iron wire and finely divided platinum. 

 The change of pressure was brought about by allowing the gases in 

 the globe to blow off into the air for a few seconds, and a reading of 

 the pressure gauge was made as soon as possible afterwards. 



The ratio of the pressures before and after the change is 

 9-1 = 1-39, and that of the ratio of decomposition (taken 

 approximately from the values of AP) is 19-6/15-2 = 1-29 



The agreement is sufficiently close to show that the reaction is 

 ally of the first order, or monomolecular, apart from the little- 

 understood disturbing influences.* 



Summary and Conclusion. 



i0n amm nia has been investigated under 

 the containing vessel was of porcelain. The 



8.. TM't Hoff. Vorlwung,' 2nd edition, p. 234. 



