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decomposition pressure of silver oxide, the gain in weight of the silver 
can be readily explained by its oxidation to silver oxide. The loss in 
weight of the silver oxide can only be explained by assuming that it 
contained water or carbon dioxide. I should consider this improbable 
if it were not for the fact that my own experiments have shown how 
difficult it is to prepare and to keep silver oxide free from these im- 
purities. It is perhaps not generally known that carbon dioxide, as well 
as water, is rapidly taken up by silver oxide from the atmosphere. One 
sample which I prepared in such a way that it was absolutely free from 
this impurity absorbed a considerable quantity of carbon dioxide while 
standing for a month in a loosely corked bottle. When carbon dioxide 
and water are once present, they can be expelled only with great difficulty. 
Some of the former frequently remains after the silver oxide has been 
heated an hour or two at 300°. 
That silver suboxide was not present in any of the experiments I have 
described will be evident from the following considerations. According 
to the phase-rule, silver, silver oxide, silver suboxide, and oxygen can not 
all exist together in equilibrium. In the absence of suboxide only one 
state of equilibrium is possible, that between Ag, Ag,O, O,. But in 
case the suboxide could form, then two states of equilibrium would be 
possible, namely between Ag,O, Ag,O, O,, and between Ag,O, Ag, O,. 
With a given quantity of silver oxide enclosed in a small volume the first 
equilibrium would exist; in a larger volume, the second. 
In all the experiments previously described the final mixture in the 
tube has contained silver, as shown by the color and by the metallic 
flakes produced upon grinding the whole in a mortar. In any given 
case, therefore, the remaining black powder must be a single phase, either 
all silver oxide or all silver suboxide. Let us assume that it is the 
latter and see to what consequences we are led. For example, let us 
assume that the pressure of 32 atmospheres which we obtained at 325° 
is the decomposition pressure of silver suboxide. Now suppose that we 
inclose so much silver oxide in a tube that if it should all decompose 
according to the reaction, 
: 4 Ag,O = 2 Ag,O + 0, 
a pressure of over 32 atmospheres would result. Then metallic silver 
could not form and the only possible equilibrium would be that between 
the oxide and suboxide. 
This very experiment was undertaken. A glass tube was filled with 
silver oxide, sealed, and heated for a week at 325°. At the end of this 
time a considerable quantity of silver had formed, although, calculated 
from the volume of the tube and the amount of oxide, over 100 atmos- 
pheres would have been generated by the change from the oxide to the 
suboxide alone. A similar experiment was made at 345°. A small 
quantity of silver was placed in a tube and covered with a little glass wool. 
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