AUTOCATALYTIC DECOMPOSITION OF SILVER OXIDE. 



By Gii.itERT X. Lewis, IMi. I)., J'lii/siml ('hcmiKl. 



In tlie course of an investigation to determine the equililn'iuni 

 pressure at a given temperature in the system 2Ag20 = 4Ag + Oj, 

 a singular phenomenon appeared. The experiment consisted 

 sim])ly in lieating silver oxide at a constant temperature of 

 335° C. , the stout glass tube which contained the oxide l)eing 

 connected with a manometer. After heating several hours the 

 manometer gave no evidence that any decomposition had oc- 

 curred. This occasioned some surprise, since 250° C. is freciuently 

 given as the temperature at which silver oxide begins to 

 decompose. As I Avas alK)ut to stop the experiment in order to 

 test the tightness of the joints I detected a slight defection of 

 the manometer. This increased considerably during the lU'xt 

 hour, and I noticed that the greater the pressure became the 

 greater became the rate of its increase, until finally the pressure 

 had reached 20 atmospheres and was increasing at the astonish- 

 ing rate of between 3 and 4 atmospheres per hour. At this 

 point the cement joining the tube and the manometer began 

 to give way and the experiment had to be discontinued. It 

 had progressed far enough, however, to stimulate considerMl))*' 

 curiosity as to the ex])lanation of so unusual a behavior. 



The graihiiil acceleration in the decomposition wbii-h was 

 observed could only be attril)Uted to one of the following causes: 

 (1) The increasing pressure; (2) the increasing concentration of 

 oxygen; (3) the accumulation of metallic silver; (4) some ebange 

 in the .silver oxide, such as the sl(»w agglonu'ration of its grains. 

 Of these four the first two were eliminated at once l»y a rough 

 experiment carried on ;it atnios|)lierii' pressnre. wbieii showed 

 the same ]iheniinienon of aeeelerating deeom[)osition. It seemed 



5 



