172 Mr Wood and Mr Jones, On Complex Carbonates. 
and the conditions for the formation of an individual salt were 
not determined. 
In order to establish the solubility relationships of copper and 
potassium carbonates a very large number of solubility deter- 
minations have been made. The determinations were all made 
at 25° C. The solutions were put in small bottles and set in a 
rotating shaker holding twelve bottles, which was immersed in 
a water-bath and kept in motion for a long time. A weighed 
quantity of the solution was first titrated with standard acid, the 
copper in the neutral solution was then estimated by adding 
potassium iodide and titrating the iodine liberated, or, it was 
estimated in a separate portion of the solution by boiling with 
excess of grape sugar, dissolving the precipitated cuprous oxide 
in ferric sulphate and titrating the ferrous salt produced with 
potassium permanganate. The amount of potassium carbonate 
present was then found by subtracting the amount of acid 
necessary to react with the copper carbonate from the total 
amount used and calculating the potassium carbonate equivalent 
to the acid left. At first precipitated basic copper carbonate 
was used as the source of copper. As long as solid potassium 
carbonate was present in excess, fairly consistent results were 
obtained in separate experiments, the results of these agree with 
those represented on the ascending portion of the curve from 
A to B. 
In the more dilute solutions however most erratic results were 
obtained, the amount of copper carbonate dissolved seemed to 
depend on the amount that had been added as solid. This was 
found to be due to the interaction of the copper hydroxide with 
the potassium carbonate in solution producing potassium hydrate 
and so altering the conditions. It was then found that solutions 
containing from 90 to 100 grams of potassium carbonate in 
100 grams of water which had been saturated with basic copper 
carbonate contained about 3 5 grams of copper carbonate in the 
same quantity of water and deposited blue hexagonal plates of a 
double copper potassium carbonate on standing in the cold. This 
salt was found to be identical with that prepared by Reynolds. 
The preparation of this salt in quantity will be described later. 
This double salt was afterwards used as the source of copper 
and the solutions were saturated in contact with the double salt. 
The solutions in equilibrium with potassium carbonate as solid 
phase, represented by the points on the curve between A and B, 
had practically the same concentrations of copper carbonate now 
as when basic copper carbonate had been used. The point B at 
which the solution is in equilibrium with the two solid phases 
potassium carbonate and double salt, could be determined with 
fair accuracy, the solution then contains 105 grams of potassium 
