840 REPORTS ON THE STATE OF SCIENCE.—1912. V.C. iti, 
tration of the non-ionised portion of a salt in solution has the same value 
in dilute solutions of other salts as when alone. In this connection Noyes 
and Bray *°* made an examination of the solubility of certain salts in the 
presence of some other salt which give a common ‘ ion’ when in solu- 
tion, e.g. potassium sulphate and silver sulphate, and found that in sll 
cases examined the ‘ ionic solubility-product ’ was increased so much that 
the ‘ law ’ was not even approximately true. In some few isolated cases, 
recorded by Noyes, Boggs, and others,4°*, approximate agreement was 
observed and the discovery of an example in fair agreement with the 
** law ’ was published by Bray and Winninghoff;*°7 they having found 
that potassium nitrate and sulphate occasion an increased solubility of 
thallous chloride, whilst thallous sulphate diminishes it. Bray,‘ 
reviewed the work referred to above, and concluded that the concentra- 
tion of the non-ionised portion of salt is not constant but usually 
diminishes, and the ‘ ionic solubility-product ’ usually increases. His 
attempt to express the observed variations as functions of the total 
“jon concentration ’ led to no real advance being made. 
This line of work was continued by Harkins,*°® who came to the 
conclusion that with solutions of uni-bivalent salts, the addition of a 
salt giving a common univalent ‘ ion’ lowered the solubility in accord- 
ance with the principle of the ‘ solubility-product.’ The addition of a 
salt giving a common bivalent ‘ion,’ however, produced changes 
entirely different from those anticipated. A salt with no common 
‘ion’ always increased the solubility of the first salt. Further work 
was published by Harkins and Winninghoff,*!® and Harkins *! also 
contributed a discussion of the results from the standpoint of the ‘ ionic 
dissociation ’ hypothesis. ; 
With the object of testing the constancy of the ‘ ionic solubility-pro- 
duct,’ Kendall +4* measured the solubility of sparingly soluble acids in 
aqueous solutions of a second acid, the experiments being ordered so 
as to give combinations of two weak acids, of a weak and a strong acid, 
and of two strong acids. The results obtained showed considerable 
divergences from the values required by the theory of a constant ‘ ionic 
solubility-product.’ These differences were attributed in all cases to 
the solvent power exerted by the second acid in solution. 
Herz **” found that hydrogen chloride and hydrogen bromide are 
equally effective in lowering the solubility of succinic acid in water, and, 
with the exception of lithium chloride, are more powerful in this respect 
than are the alkali salts. It was observed also that tartaric and racemic 
acids increase the solubility of boric acid by an equal amount. In a 
subsequent publication this author *!® recorded results of work dealing 
with the solubility of salts of the alkali metals in aqueous solutions 
of their corresponding acids. 
Masson ** undertook an extension of the research made by Engel 
with the object of elucidating, if possible, the conditions governing the 
dissolution of salts in aqueous solutions of their acids, for those cases 
where Engel’s rule is not obeyed. He found the rule of equivalent 
precipitation to be of limited applicability and deduced a differential 
equation which expresses the relationship between the concentration of 
acid and of salt. * 
