VII. : ON SOLUBILITY. 849 
Findlay '** applied to the case of solubilities the equation* R=R'+C 
(t'—t) developed by Ramsay and Young} to represent the relation be- 
tween the vapour pressure of two substances. He found that if the 
solubility graph of one substance is known, then if two observations of 
solubility of the second substance at different temperatures are made, 
the solubility of the second substance at any absolute temperature can 
be calculated. This method was adopted in the case of several salt 
pairs,!?? also when measuring the solubility of mannitol, picric acid, and 
anthracene, !** and was extended to other cases in a later publication.**? 
The application of the electrolytic dissociation hypothesis to the 
calculations of solubility from conductivity measurements is liable to 
lead to erroneous results, and this is clearly shown by the work of Noyes 
and Kohn.'42 Kohlrausch, when calculating the solubility of silver 
chloride by the method referred to, assumed that silver hydroxide is com- 
pletely dissociated in solution: by direct analysis Noyes and Kohr, how- 
ever, obtained results which were not in agreement with Kohlrausch’s 
and which led them to conclude that the hydroxide is only dissociated to 
the extent of 70 per cent. 
The relationship between freezing point, boiling point and solubility 
was discussed by Wildermann,'*® and as a result, this author devised 
certain mathematical equations from which the solubility graphs for a 
substance dissolving in water could be calculated. 
Lumiére, Lumiére and Seyewetz °° made the interesting observa- 
tion that the solubilities of trioxymethylene and sodium sulphite in 
water are increased by the presence of each other, and they suggest 
this may be due to partial depolymerisation taking place in the solution. 
1903 The subject of the velocity of dissolution was again taken up 
‘by Bruner and Tolloczko.'8* They experimented with alabaster 
and gypsum and found that the velocity is not a linear function of 
time, as Drucker deduced, but in the case of alabaster is a logarithmic 
function. 
An experimental examination of the thermodynamical relation be- 
tween the heat of solution and change of solubility with temperature 
in the case of dissociated substances was undertaken by Noyes and 
Sammet.1** They made use of o-nitro-benzoic acid and potassium 
perchlorate, and although the results obtained in the case of the former 
substance were not in good agreement, those with potassium perchlorate 
were in approximate agreement with the requirements of Van’t Hoff’s 
equation, so these authors expressed the opinion that electrical conduc- 
tivity is a correct measure of dissociation. 
According to Bogdan,'"* non-electrolytes increase and electrolytes 
diminish the solubility of phenylthiocarbamide, whereas both electrolytes 
and non-electrolytes increase the solubility of boric acid. This author 
contributed also a lengthy discussion of the theories of Jahn and Nernst. 
* In this equation R and R’ represent the ratios of the absolute temperatures at 
two points of equal solubility of the substances ; c is a constant and ¢’ and ¢ are the 
temperatures at which the solubility of the second substance is known. 
Notr.—Meyerhoffer' credited Kopp (Vide Part I. R. 10) with the discovery that 
each hydrate of a salt has a definite solubility graph. Ostwald,’ however, attributed 
this discovery to Gay-Lussac. 
} Vide Phil. Mag., 21, 33. 
1912. 31 
