The question may be raised, why the first solvents mentioned should have the power to cause ionization, while the second series of solvents named do not have this power, or have it only to a very slight extent. Without attempting to enter into an elaborate discussion of this important question, it may be said that J. J. Thomson[101] and Nernst[102] suggested that the ionizing powers of solvents must be intimately connected with their ‹dielectric behavior›, and this view has now been well established. It may be said, in simple terms, that the so-called dielectric constant of a solvent determines the force with which electrical charges will attract and repel each other; the higher the dielectric coefficient of a medium, the ‹smaller will be the attraction between opposite electrical charges›, other conditions being the same. In solvents, then, of high dielectric powers, the coëxistence of oppositely charged particles must be more favored than in solvents of low dielectric powers. The dielectric constants of a number of solvents are given in the following table: [p063] Hydrogen cyanide, HNC 95 Hydrogen peroxide, H_{2}O_{2} 93 Water, H_{2}O 81 Methyl (wood) alcohol, CH_{4}O 32 Ethyl (ordinary) alcohol, C_{2}H_{6}O 22 Ammonia, H_{3}N 22 Chloroform, CHCl_{3} 5 Ether, (C_{2}H_{5})_{2}O 4 Benzene, C_{6}H_{6} 2 It is quite apparent that the good ionizing media have, as a matter of fact, the highest constants; those which cause ionization, at most minimally (‹e.g.› benzene), the lowest.