Vic. iil. ON SOLUBILITY. 835 
Although Noyes * had apparently furnished experimental evidence 
of the applicability of Nernst’s formula for calculating the solubility of 
mixtures of salts, Bullerdieck,17° working under the conditions of Noyes’ 
experiments, found evidence of the formation of complex salts in solu- 
tion, thus detracting much from the importance of this application of 
Nernst’s formula to solutions. Additional contradictory evidence was 
furnished by Bogdan,'7® who found that the solubility of boric acid in 
water is increased alike by the addition thereto of electrolytes and 
non-electrolytes. 
The variableness or fixity of composition of the undissolved residue 
when preparing solutions saturated with two separate salts was made 
use of by Foote ‘"? for determining double-salt formation. From the 
laws regulating the solubility of substances containing a common 
‘ion,’ it was argued that if the solid residue consists of two distinct 
salts, whether simple or double, their relative proportion may vary 
but the concentration of the saturated solution remains constant. 
When, however, the residue consists of only one salt, its composition 
remains fixed, whilst that of the solution may vary within limits, 
according to the relative amount of each salt originally present. 
Making use of this argument,!7* the author detects double thiocyanates 
of silver and potassium, and double chlorides of cesium and mercury. 
1904 Much attention was given in the following year to the study 
* of solubility variations of salts as caused by the presence of other 
electrolytes in the solution. Cameron and Breazeale?°* studied the 
solubility of calcium sulphate in aqueous solutions of sodium and 
potassium sulphate, and Seidel and Smith ?°* followed the changes of 
solubility of calcium sulphate in solutions of sodium and magnesium 
nitrate. The presence of these salts was found to occasion an in- 
creased solubility of the sulphate, but the presence of calcium nitrate 
conditioned a decrease. 
Groschuff 1** determined the solubility of acid nitrates of potassium 
and ammonium in aqueous solutions of nitric acid, and discussed his 
results from the standpoint of the equilibrium theory. 
In connection with an inquiry into the use of mercurous sulphate 
in standard cells, Hulett 7°? examined the change of solubility of that 
salt when dissolved in sulphuric acid of various concentrations. Avuer- 
bach *** studied the solubility relations of MgCO,,3H,O and KHCO,, 
which form a double salt of the composition MgCO,,KHCO,, 4H,0, 
the solubility of magnesium carbonate in the acid carbonate solution 
being found to increase with increased concentration of the latter up to 
the point at which the double salt begins to be formed. 
When several salts are dissolved together in a solvent the mutual 
solubility influence exerted by those salts is one of the main factors 
determining the order of their deposition when the solvent evaporates. 
The problem of foretelling the order of deposition of salts from such 
complex mixtures was attacked by Van’t Hoff and his pupils. By the 
application of the Phase Rule of Willard Gibbs and the skilful use of 
diagrams constructed from certain knowledge of the solubility of the 
* Vide Part J. R. 164. 
3H 2 
