10 
Proceedings of the Royal Society of Edinburgh. [Sess. 
method, i.e. the bulb of the thermometer was imbedded in a tube containing 
the hexahydrate and the tube placed in a bath. The temperature of the 
bath was then steadily raised. The thermometer in the copper nitrate 
indicated a similar steady rise in temperature up to 24’60°, at which 
temperature it remained constant for some time, and then again rose 
steadily. 
On cooling the temperature fell steadily to 24’65°, where it remained 
constant for some time, and then again fell regularly. The thermometer 
used in these experiments was compared with a new Reichsanstalt standard, 
and the necessary corrections have been applied in the above values. 
Vapour Pressures of these Hydrates . — Attempts were made to determine 
the vapour pressure of the saturated solution, hexahydrate system, by the 
dew-point method (Cumming, Jour. Ghem. Soc., 1909, 95, 1772), but it was 
found that the silver cylinder quickly became tarnished. A cylinder was 
therefore used which was heavily plated with gold, but a deposit formed 
on this also. The deposit on the gold was found to be acid in reaction, so 
that the vapour given off from a saturated copper nitrate solution must 
contain traces of acid. The vapour pressures were not constant, and it 
appears probable, therefore, that there is considerable hydrolysis in aqueous 
solution. 
It was thought interesting to find the concentration of nitric acid, 
which would be in equilibrium with a mixture of Cu(N0 3 ) 2 , 3H 2 0 and 
Cu(N 0 3 ) 2 , 6H 2 0. The hexahydrate is dehydrated by concentrated nitric 
acid, and this continued until the nitric acid was about 40 per cent. HN0 3 . 
The trihydrate is hydrated to the hexahydrate by dilute nitric acid, and 
this process was found to proceed until the concentration of nitric acid had 
risen to about 20 per cent. HN0 3 . At this stage the actions have 
apparently stopped, so the expected equilibrium has not so far (after 
several months) been attained. Further experiments, however, on the 
vapour pressure phenomena are contemplated. 
Summary. 
1. Graham states that when nitric acid of specific gravity greater than 
1*4 acts on copper oxide a basic nitrate is obtained. We were unable to 
obtain a basic salt under these conditions. 
2. Copper oxide and approximately 100 per cent, nitric acid yield 
copper nitrate trihydrate, nitrogen peroxide, and oxygen. The equation 
for the reaction is probably 
CuO + 6HN0 3 = Cu(X0 3 ) 2 , 3H 2 0 + 4N0 2 + 0 2 . 
