6 
Proceedings of the Royal Society of Edinburgh. [Sess. 
copper oxide was prepared by ignition of the nitrate. The copper oxide 
was placed in the bulb A of the apparatus shown in the figure, and the 
nitric acid in the bulb B. The air was swept out of the apparatus by a 
current of C0 2 , and the nitric acid then poured on to the copper oxide. 
No interaction occurred until the mixture was heated to 70°. The evolved 
gases were drawn by a slow stream of carbon dioxide into the empty bottle 
C, which was kept in a freezing mixture at a temperature below — 5°. 
After passing through this cold bottle the gases no longer attacked rubber 
and could, therefore, be led by a rubber tube to the gas burette D. In a 
preliminary experiment an evacuated apparatus was used, but the nitric 
acid then distilled off from the copper oxide, leaving it only slightly acted 
upon. This was the reason for filling the apparatus with carbon dioxide. 
The gas burette was filled with concentrated potash to absorb carbon 
dioxide and nitrogen peroxide. In an experiment in which 1-5 grms. of 
copper oxide and about 8 c.c. of nitric acid were mixed, the amount unab- 
sorbed by potash was 109 c.c. This was found to consist of 7*2 c.c. of oxygen 
and 37 c.c. of nitrogen. The carbon dioxide contained a little air, but the 
amount of nitrogen was somewhat higher than was expected, though the 
amount of carbon dioxide used was not known. There is no question, however, 
