1911-12.] Preparation and Properties of Basic Copper Nitrate. 9 
Copper Oxide mid Nitric Anhydride. — One object of these experiments 
was the preparation of anhydrous copper nitrate, but our results offered 
little hope of its isolation by dehydrating the trihydrate, even at ordinary 
temperatures. In all cases dehydration was accompanied by further 
decomposition and formation of a basic salt. 
It was thought possible that copper oxide and nitric anhydride would 
combine, and experiments were therefore tried, to ascertain if anhydrous 
copper nitrate could be made in this way. The copper oxide was prepared 
by ignition of the nitrate, and was strongly heated immediately before use 
to expel any traces of moisture. Nitric anhydride was prepared from 
fuming nitric acid and phosphorus pentoxide by the method recommended 
by E. Gibson ( Proc . Roy. Soc. Edinburgh), and obtained as hard transparent 
crystals, which were mixed in a sealed tube with about one-third the bulk 
of copper oxide. Some of the nitric anhydride still remained after several 
days, but no change in the copper oxide could be detected. The nitric 
anhydride decomposed, leaving a yellow liquid, and the decomposition 
apparently went on at about the same rate as with a sample of nitric 
anhydride sealed alone in a tube. Incidentally it may be mentioned that 
liquid nitrogen peroxide was also found to have no action on copper oxide. 
No action occurred when copper oxide and crystals of nitric anhydride 
were heated together in a dry test-tube until all the nitric anhydride had 
evaporated. 
Equilibrium between the Hexahydrate and Trihydrate. — There are 
several references in the literature to the equilibrium conditions of the 
reaction 
Cu(N0 3 ) 2 ,6H 2 0 = Cu(N0 3 ) 2 , 3H 2 0 + 3H 2 0, 
but the only recent and exact work on the subject appears to be the 
solubility determinations of Funk (Z. anorg. Ch., 20, 412, 1899). According 
to his results the transition temperature is 24*5°, while the hexahydrate has 
a metastable melting point at 25*4°. 
We obtained by the dilatometer method the following values for the 
transition temperature : — 
Rising temperature, 24*7°, 24*75°, 24-60°, 24*60° 
Falling temperature, 24*65°, 24*70° 
} 
mean = 24*66° (corr.). 
In performing the first dilatometer experiment, it was found that there 
was a well-marked break at the transition temperature, and when the 
warming was continued there was a further abrupt break in the curve at 
25'6°. This probably indicates the melting point of the (metastable) 
hexahydrate. 
The transition temperature was also determined by the thermometric 
