190 NON-METALS AND THEIR COMBINATIONS. 



abnormally large values of freezing-point depressions, boiling-point 

 elevations, and osmotic pressures. In the discussion of the latter 

 subjects (which see) it is pointed out that the abnormally acting sub- 

 stances behave as if there are more particles in solution than the 

 number of molecules corresponding to the weights of the substances 

 dissolved, which fact can be accounted for only on the supposition 

 that some molecules are decomposed by the solvent into smaller par- 

 ticles. Further, since molecules which, like those of sugar, act nor- 

 mally in regard to freezing-point, boiling-point, and osmotic pressure 

 phenomena, and thus show no indication of decomposition by the 

 solvent, do not conduct electricity, it follows that the fragments of 

 decomposed molecules must be responsible for the ability to conduct 

 in the case of solutions of electrolytes. In electrolysis (see page 82) 

 these fragments are the particles that are attracted to the charged 

 poles, hence the further assumption is made that the fragments (or 

 ions as they are called) are themselves charged with electricity, be- 

 cause it is known that electricity attracts only bodies that possess a 

 charge of electricity. Briefly summed up, then, the THEORY OF 

 ELECTROLYTIC DISSOCIATION assumes that molecules of electrolytes 

 when dissolved in water break up to a varying degree into independent 

 particles charged with electricity, and that the nature and number of 

 these charged particles determine to a large degree certain physical and 

 chemical properties of solutions. 



This theory was proposed by the Swedish physicist Arrhenius in 

 lSS7 its general adoption has been hastened by the work of van't 

 Hoff, Ostwald, and Nernst. 



The dissociation of molecules in solution is also called IONIZATION, 

 and the electrically charged particles are called ions. These are al- 

 ways of two kinds, namely, electro-positive ions, or cations, because 

 they are attracted to the negative pole or cathode during electrolysis, 

 and electro-negative ions, or anions, because they are attracted to the 

 positive pole or anode. Since solutions are themselves electrically 

 neutral, that is, show no charge of electricity as a whole, it follows 

 that the sum of the electric charges of the positive ions equals the 

 sum of the charges of the negative ions. The two kinds of ions are 

 in electrical balance. 



Composition of ions. This is learned from a study of the pro- 

 ducts that are attracted to the anode and cathode, respectively, in 

 electrolysis, and from the manner in which molecules of electrolytes 

 exchange their parts or radicals in chemical actions. In molecules 



