THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XXIX. — A71 Experimental Investigation into the Exist- 

 ence of Free Ions in Aqueous Solutions of Electrolytes ; 

 by Julius Olsen.^ 



Yan't Hoff in ISSTf showed that the gas laws of Boyle, 

 Gay-Lussac, and Avogadro, hold also for dilute- solutions. 

 From considerations of osmotic pressure, theoretically and 

 experimentally, he was able to apply Avogadro's law to solu- 

 tions, and gave it as follows : 



" The pressure which a gas exerts at a given temperature, if 

 a definite number of molecules is contained in a definite vol- 

 ume, is equal to the osmotic pressure produced by most sub- 

 stances under the same conditions, if they are dissolved in any 

 given liquid." 



These laws may be combined in the well known expression 

 PV = RT 

 which holds for most substances, where P is the osmotic pres- 

 sure and Y, T, and R, as in the gas law, are volume, absolute 



PY 



temperature, and = -^ for a perfect gas, respectively, and in- 

 cludes Avogadro's law if we consider kilogram-molecules of 

 the substances, as Horstmann has shown. 



Yan't HofE found that the above expression held for most 

 substances, but there were many important exceptions. These 

 exceptions were the acids, bases, and salts ; in these the osmotic 

 pressures were greater than the law required. In other w^ords, 

 he found that the solutions with abnormal osmotic pressures 

 were the electrolytes. He accordingly introduced into the 

 expression the coefficient i and wrote it 



PY = ^RT 



* An abstract of a thesis presented to the Graduate Faculty of Yale Uni- 

 versity for the degree of Doctor of Philosophy. 

 fZeitschr. Phys. Chem., i, 481, 1887. 



Am. Jour. Sci. — Fourth Series, Yol. XIY, No. 82. — October, 1902. 



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