LIFE AND ENERGY 25 



other is by means of the charges on the ions, each ion carrying a 

 definite quantity. There are various other reasons for regarding 

 this as the correct account of the phenomena (P., p. 173). 



It has been agreed to denote the possession of a positive charge 

 by the addition of a dot to the chemical symbol of an ion, and a 

 negative charge by a dash. Thus the hydrogen ion is H', the 

 chlorine ion is CT. Ions may possess more than one charge, 

 according to their valency. Thus, sulphuric acid dissociates into 

 two H- ions, and one SO" ion, which must have two dashes to 

 satisfy the positive charges of the two hydrogen ions. 



Since it is by the agency of water that the dissociation into 

 ions is effected, it is natural to expect that the more water there is 

 in proportion to the solute, the greater will be the degree of 

 dissociation. We have seen that 0.154 molar sodium chloride is 

 almost completely dissociated into its two ions, since it is equal in 

 osmotic pressure to a 0.3 molar solution of a substance which is not 

 dissociated (E., p. 170). 



Acids and alkalies, as well as neutral salts, conduct electrical 

 currents excellently ; in fact, better than neutral salts. What are 

 the ions here? And why do they conduct better? In the case 

 of itcids, we find that hydrogen gas is given off at the cathode, 

 therefore the ion must be hydrogen with a positive charge. In the 

 case of hydrochloric acid, the other ion must be chlorine. All 

 acids are actually found to give hydrogen ions, while the anion 

 varies with the chemical composition of the acid. Alkalies deposit 

 the metallic or similar ion at the cathode. Sodium hydroxide is 

 decomposed into sodium and hydroxyl ions, but since the sodium 

 combines with water giving off hydrogen, it is this gas that actually 

 makes its appearance. At the anode, oxygen is given off, because 

 the OH when deprived of its charge cannot exist Two OH ions 

 unite, forming one molecule of water, and giving off oxygen. 



It remains to mention briefly why some electrolytes, as Faraday 

 called those substances which conduct electricity when dissolved in 

 water, are better conductors than others. It has been found by 

 experiments, which cannot be described here, that different ions 

 move to their respective poles at different rates, and according to 

 their dimensions. H and OH ions move much faster than any 

 other ions. It is easy to see that the way in which electricity is 

 carried through a solution is by means of the charges carried by 

 moving ions, so that the more rapidly these ions move, the more 

 they carry across in a given time. Hence, substances which dis- 

 sociate with the production of rapidly moving ions are better con- 

 ductors than those producing slowly moving ions. 



Ions have also the property of attaching molecules of water, 

 which increase their dimensions, and make them move more slowly. 



