Mr Wood and Mr Jones, On Complex Carbonates. 173 
carbonate and 3T5 grams of copper carbonate in 100 grams of 
water. 
The points on the curve between B and C represent solutions 
in equilibrium with double salt as solid phase. The results here 
begin to be slightly less regular and it is evident that some 
disturbing cause is coming into action. One cause of these ir- 
regularities is probably the existence of copper carbonate in a 
complex salt in solution instead of in a double salt (see later). 
Ordinates, grams of CuC0 3 per 100 grams water. 
Abscissae, ,, ,, K 2 C0 3 ,, ,, ,, ,, 
All attempts to fix the point at which the solution is in equi- 
librium with the two solid phases double salt and copper carbonate 
were futile, since the latter substance is not capable of existing 
alone and at once decomposes partially into carbon dioxide and 
copper hydrate. This naturally causes the formation of potassium 
bicarbonate in the solution and so alters the conditions. For the 
same reason the remainder of the curve which should represent 
solutions in equilibrium with copper carbonate could not be 
traced : if the double salt were added at the beginning, then the 
solution would contain amounts of bicarbonate depending on the 
amount of double salt added; and on the other hand if basic copper 
carbonate were added at the beginning, then the solution would 
contain varying amounts of potassium hydroxide depending on 
the amount of copper that had been dissolved. The presence of 
the bicarbonate in the first case and of potassium hydroxide in 
