CARBON DIOXIDE OF THE OCEAN 591 
salts of the original mixture have an ion in common with the 
new salt (as for instance Clin Na Cland KCl), then the product 
of the ionic concentration of each salt is increased. Now if, 
before mixing, this product for either salt nearly equaled its 
constant of solubility, the increase may be enough to bring 
about precipitation. If, for instance, to a solution of lead chlo- 
ride, which is not altogether insoluble in water, is added a 
sufficiency of K Cl, this addition. causes a precipitate of lead 
chloride, since the addition of the Cl ions of the potassium 
chloride causes the product Pb x Cl? to be larger than K 
where Pb =concentration of lead ions, and Cl = concentration 
of chlorine ions. . 
If, however, the salt added has no ion incommon with ions 
of the other salts, it will take away from the ions of all the 
salts to form some of all the undissociated salts that result from 
the combination of the two new ions with all the ions of the 
original salts, therefore the product of ionic concentration for 
all the salts is decreased, or, in other words, the solubilities of all 
the salts are increased. Hence, 
Proposition 3.—In a mixture of salts those with a common 
ion increase the ionic concentration of each, aiding precipitation, 
and those without a common ion decrease ionic concentration of 
each, and retard precipitation, each increasing the solubility of 
the other 
Hydrolytic dissociation.—Water, which is one of the weakest 
of acids, is itself dissociated into hydrogen and hydroxy] ions 
(HO z= + OF); but this takes place to a.very slight 
extent only. Kohlrausch found that at 18° C. for water dis- 
tilled in a vacuum there is less than one gram of hydrogen ions 
in two million liters of water,t and Ostwald, Arrhenius, and Weis, 
and Kohlrausch? in later experiments (see reference below), 
found about one-sixth of this dissociation by other methods. 
Of course these free ions will react with ions of the salts in 
tW. NERNST: Theo. Chem., pp. 658-662. 
2F, KOHLRAUSCH and AD. KEYDWEILLER, Zeits. f. Phys. Chem., XIV, pp. 
317-330. 
