449) 
The rest of the tube was filled as full as possible with silver oxide. The 
tube was then sealed and left in the thermostat for five days, at the end 
of which time not only was the silver unoxidized but white spots of silver 
had appeared throughout the oxide. 
These experiments show pretty conclusively the absence of silver 
suboxide. A still stronger proof is given by the experiments at 302°. 
In one of the experiments at this temperature which showed the pres- 
sure of equilibrium to be about 20 atmospheres, the volume of the tube 
and the manometer and the weight of silver oxide were determined. It 
was found that enough oxide had been used to produce a pressure of 35 
to 40 atmospheres if it had all changed to suboxide, yet a considerable 
quantity of silver was found in the final mixture. 
Finally, it was found possible to show by direct analysis that the black 
powder left in the tubes was not silver suboxide. It sometimes happened 
that at the end of the experiment the silver oxide was almost entirely de- 
composed in one part of the tube and apparently unchanged in another. 
This was due to the fact that the decomposition being autocalytic in 
character, progresses very rapidly at any point where it has once begun. 
In the first experiment at 302° a considerable portion of the black sub- 
stance left in the tube appeared to contain no silver. A sample of this 
weighing 0.0892 grams was heated in a tube connected with a gas burette. 
It yielded 4.71 cc. of oxygen (at 27°, 760 mm.). The above quantity of 
pure silver oxide should give theoretically 4.73 ce. This is an unex- 
pectedly good agreement. 
In the experiments at 445° there was no case in which the remaining 
oxide did not contain some silver, but two samples were chosen which 
appeared to be least decomposed ; 0.205 grams of the first: gave 7.24 ce. 
of oxygen (calculated for Ag,O, 10.85 cc.; for Ag,O, 5.42 ce.) ; 0.0851 
grams of the second gave 4.35 cc. (calculated for Ag,O, 4.52 ce.; for 
Ag, O, 2.26 ec.). It is obvious that here also the black substance can 
not be silver suboxide and is presumably silver oxide mixed with a certain 
amount of silver. 
THE HEAT OF FORMATION OF SILVER OXIDE. 
We have now obtained the pressure of equilibrium at different tem- 
peratures between silver, oxygen, and a certain black powder. We have 
proved that this black powder is not silver suboxide, but that at 302° 
and presumably at the other temperatures as well, it has exactly the 
composition, Ag,O. ‘There still remains the possibility that this sub- 
stance, although of the same composition as the silver oxide which 
exists at ordinary temperatures, may be an allotropic phase. In other 
words, there may be a transition temperature between room temperature 
and the tem eratures of our experiments at which a break in continuity 
EF - ilver | oxide occurs. — This | - possibility must be 
can safely calculate the decomposition ; pressure of 
‘silver oxide at 25° from the pressures at the higher temperatures. 
Agr ;+ 
Lane Ce’ | hae 
