174 Mr Wood and Mr Jones, On Complex Carbonates. 
the second was demonstrated by titration with acid, using first 
phenolphthalein and then methyl orange as indicators. The 
dotted line therefore shows the general course of the curve only 
and is approximately the mean between the points representing a 
very large number of determinations. 
Sometimes when attempting to get points in the neighbour- 
hood of the point C it was found that the solid at the bottom of 
the solution instead of being the amorphous green basic copper 
carbonate was the black hydrate, in these cases the solutions had 
been allowed to stand a very long time and their compositions 
which are represented by points near D are not on the curve. 
It is clear that the conditions for the existence of the double 
salt are determined by the curve, it can exist in contact with 
solutions with compositions between those represented by the 
points B and C. In order to prepare large quantities of the salt 
a sample of basic copper carbonate was prepared and analysed, its 
composition was represented by CuC0 3 Cu(0H) 2 2H 2 0. A solution 
of potassium carbonate containing about 100 grams in 100 grams 
of water was made and shaken for several days with a mixture of 
the basic copper carbonate, potassium carbonate and bicarbonate 
in the proportions required by the equation : 
CuC0 3 Cu(0H> 2 2H„0 + 2KHC0 3 + K 2 C0 3 
= 2CuC0 3 K 2 C0 3 + 4H 2 0. 
After several days the green basic copper carbonate had been 
completely converted into the blue hexagonal crystals of the 
double salt. The double salt was then filtered from the mother 
liquor with the aid of the pump and was dried by pressing 
between layers of filter paper until the paper was no longer 
damped. The salt obtained in this way is identical with that 
obtained by Reynolds, but in some cases was found to be con- 
taminated with potassium bicarbonate. 
The double salt decomposes in contact with water, potassium 
carbonate and a very small quantity of copper carbonate going 
into solution and basic copper carbonate remaining insoluble. It 
dissolves in a solution of potassium carbonate of sufficient con- 
centration, i.e. a solution containing more than 85 grams of 
potassium carbonate to 100 grams of water, to form deep blue 
solutions. These solutions become turbid on diluting with water, 
but, if not saturated with copper carbonate, do not change on 
boiling for some time. Solutions prepared from basic copper 
carbonate at once give on heating a black precipitate of hydrated 
copper oxide, the formation of this precipitate is prevented by 
the addition of potassium bicarbonate and the solutions which are 
stable on boiling at once give a precipitate if a little caustic 
potash be added to the hot solution. It is clear therefore that the 
