The Romance of Modern Chemistry

FACTS ABOUT SOLUTIONS appears to be no sufficient reason why mere contact with water should induce sodium chloride and other electrolytes to commit “ molecular suicide,” as one critic has put it The question of a motive for this “ suicide ” has been a difficulty, but recent work indicates that the ions have a greater affection for water than they have for each other, and hence arises their apparent readiness to part company. Whether this be the correct explanation or not, it is certain that the Arrhenius hypothesis of ionic dissociation gives an excellent in- terpretation of many properties of solutions, and has provided a basis for much valuable work. How, then, does it explain the fact that salt has an abnormally big influence on the freezing-point of water ? Simply in this way, that such a dissociation of sodium chloride as has been suggested would mean an excep- tionally large number of dissolved units, and since the depression of the freezing-point is proportional to the number of dissolved units, the effect of the salt on the freezing-point is unexpectedly great Then, again, the fact that sodium chloride makes water a conductor of the electric current becomes in- telligible on the basis of Arrhenius’ hypothesis. For if the salt solution contains a large number of positively and negatively charged particles, the mere immersion of two battery wires will cause a streaming of the 4-ions to the negative wire, and. of the —ions in the opposite direction. Such a procession of ions carrying electric charges is nothing else than a transport of electricity, and is therefore equivalent to the passage of a current through the solution. The presence of the salt, that is, has changed the water from a non-conductor to a conductor. 312