CONCERNING SILVER OXIDE AND SILVER SUBOXIDE. 
By Giiperr N. Lewis. 
(From the Chemical Division, Bureau of Science. ) 
On account of the uncertainty as to the correctness of the value at 
present accepted for the electrolytic potential of oxygen, I have attempted 
to calculate this extremely important quantity by an indirect method. 
One very necessary datum needed in this calculation is the decomposition 
pressure of silver oxide at 25°. The determination of this pressure is 
the subject of the present paper. Incidentally it will be necessary to 
consider the suboxide of silver which, by certain chemists, has been sup- 
posed to exist. 
LeChatelier * was the first to show the reversibility of the reaction, 
2 Ag,O =4 Ag+ O,. 
By the decomposition of silver oxide in a closed tube at 300° he obtained 
a pressure of 10 atmospheres. On the other hand, by heating silver at 
the same temperature in oxygen at 15 atmospheres he observed the 
oxidation of the silver. He therefore placed the decomposition pres- 
sure of silver oxide between 10 and 15 atmospheres. 
Knowing this pressure for one temperature, and the heat of decom- 
position, it should be possible to calculate with the aid of the van’t 
Hoff equation, the pressure at another temperature. However, such a 
calculation must be made with great caution. In the first place, we 
must be sure that at both temperatures we are dealing with precisely the 
same reaction. 
Guntz? has undertaken to show that the pressure he obtained by 
heating silver oxide at 358° was not the decomposition pressure of silver 
oxide but of silver suboxide. In other words, he believed that silver oxide 
at first decomposed entirely into suboxide and oxygen, according to the 
equation, 
4 Ag,O = 2 Ag,O + O,, 
and that the suboxide then partially decomposed until equilibrium was 
reached, according to the equation, 
2AgO=8Ag+O,.. | 
Zeit, Phys. Chem. (1887), 1, 516. 
°C. R. 128 (1899), 996. 
439 
