722 PROCEEDINGS OF THE AMERICAN ACADEMY. 



perature of the room. The end of this brass tube was connected with a 

 gas burette (K) and to the recorder (L). This latter was simply a glass 

 tube about 2 mm. in diameter, marked off at such intervals that the 

 volume from one mark to the next was exactly 1 c.c. A small column 

 of water (M) served as index. With stopcock H closed and I open, the 

 small water column advanced along the recording tube, and the time 

 taken by the forward meniscus in moving from one mark to the next was 

 read with a stop-watch. When the reaction was very fast the recording 

 meniscus was allowed to run through several centimeters in order to per- 

 mit a more accurate measurement of the time. Thus it was possible to 

 measure accurately the rate of evolution of oxygen, whether 1 c.c. in an 

 hour or 1 c.c. in ten seconds, the latter being the greatest velocity measured. 

 After measuring the reaction velocity, the water indicator could be brought 

 back to its initial position by cautiously opening the stopcock (H). I was 

 then closed and H left open, thus allowing the gas to collect in the bu- 

 rette until the velocity was again meas'Ured. In this way the velocity at 

 any moment, and the total volume of gas that had been evolved, could be 

 measured independently. After the first few experiments, however, the 

 burette was done away with, and only the velocity was measured, as it 

 was found that in the few cases where a knowledge of the total volume 

 was desired it could be ascertained with sufficient accuracy by a rough 

 measurement of the time-velocity curve. 



This simple apparatus gave complete satisfaction, cleanliness in the 

 recording tube being the only precaution necessary for its success. 



The Course of the Reaction. 



In the first experiment with the apparatus 4. 1 grams of silver oxide 

 were used, the temperature was 327.5^ C, and the measurements of the 

 reaction velocity were made for twenty-four hours at intervals of one half 

 to one hour. For several hours the decomposition was inappreciable ; at 

 the end of ten hours the rate was 1 cc of oxygen evolved per hour ; after 

 thirteen hours, 1 c.c. in twenty-seven minutes ; after fourteen hours, 1 c.c. 

 in eighteen minutes; after sixteen hours, in four minutes ; after eighteen 

 hours, in one and one half minutes, and at this point the velocity was 

 increasing rapidly. After twenty hours the rate was 1 c.c. in one minute, 

 and rapidly falling, showing that between the last observation and this 

 a point of maximum velocity had been reached. After twenty and one 

 half hours the rate of evolution was 1 c.c. in two minutes; after twenty- 

 one hours, 1 c.c. in three and one half minutes ; after twenty-one and 



