LEWIS. — AUTOCATALYTIC DECOMPOSITION OF SILVER OXIDE. 723 



a Imlf hours, in seven minutes ; and before twenty-four hours had passed 

 all action had ceased. 



This experiment gave a general idea of the course of the reaction. At 

 the beginning the velocity is very small, increasing more and more rapidly 

 to a maximum, then falling, rapidly at iirst, later more slowly, until finally 

 the reaction is complete. This decomposition has the general character 

 of an explosion, and in fact it is nothing more or less than an explosion 

 which is slow enough so that its velocity can be measured, and differing 

 from the ordinary explosion only in that the latter is a reaction which 

 progresses with accelerating velocity because of increasing temperature 

 due to the heat given off by the reaction, while the decomposition we are 

 studying takes place at constant temperature, and is in fact an endothermic 

 reaction. 



To find the cause of the acceleration in this case was the next problem. 

 Two possible explanations were left. The phenomenon might be due to 

 a gradual physical change in the silver oxide, such as to bring it into a 

 more and more reactive condition, or it might be due to the presence of 

 the silver produced in the reaction. The latter supposition could fortu- 

 nately be tested directly by experiment, for if the silver formed by the 

 reaction were a catalyzer, then unquestionably silver prepared in the 

 same way and mixed with the oxide before the experiment would pro- 

 duce a similar effect. Therefore, the preceding experiment was repeated, 

 using instead of the pure silver oxide a mixture of 5.5 grams of oxide 

 and 0.1 of a gram of the powdered metallic silver obtained from the last 

 experiment. These were rubbed together until very intimately mixed. 



Noticeable decomposition began as soon as the mixture was put into the 

 thermostat. The rate of evolution of oxygen after two hours was 1 c.c. 

 in five minutes ; after five hours, in three minutes ; after seven hours, in 

 one and one half minutes ; after about eight hours the maximum of 1 c.c. 

 per minute was reached, and in twelve hours the reaction was over. 



In the last experiment the reaction at the end of twelve hours was just 

 beginning to have a measurable velocity. This difference between the 

 two experiments seemed to point conclusively to catalytic action by the 

 silver. Yet, it is not inconceivable that the difference might be due to 

 some difference in the treatment of the two samples of silver oxide. In 

 order to remove this doubt the following experiment was tried later, under 

 new conditions, with a different preparation of silver oxide, and at a 

 different temperature. 



Three portions of silver oxide were taken, each w^eighing 3.3 grams. 

 To the first (A) 1.1 grams of silver powder was added, to the second (B) 



