«Influence of Light and Heat.»—It is apparent that heat, a form of energy, contributes to the dissociation of ionogens, and it is natural that we should consider other forms of energy, ‹e.g.› light, to have the same power. One may speculate about the possibility of light inducing chemical action (‹e.g.› in starting the combination of hydrogen and chlorine, or in photography) by its ionizing power, and about the possibility that rapid combination of oxygen and hydrogen follows the application of a flame to the mixture, as the result of increased ionization of the components at the elevated temperature of the flame and of the burning gases. The experimental evidence shows that, in some actions of this nature, ionization is an important factor, while in other instances it appears to be negligible.[135] [p077] «Conclusions.»—It appears that we must accept the conclusion, that the ‹reactions of salts›, ‹acids› and ‹bases› (ionogens) ‹in aqueous solution› (the so-called "salt reactions") ‹are the reactions of the ions and not of the non-ionized molecules.› This conclusion is of the greatest and most practical importance in our science. It is the natural inference from the results of the qualitative experiments described in the three preceding sections. Its final adoption, however, is based on the existence of a great mass of ‹quantitative evidence›, and to the consideration of some of this we now turn. «Quantitative Relations.»—If the active components in aqueous solutions of acids, bases and salts are the ions, rather than the undissociated compounds, then quantitative data supporting such a conclusion should be found. Such quantitative confirmation, from the point of view of chemical activity, is not lacking. Only a small part of the data can be considered here. Conductivity measurements, and the lowering of freezing-points and the elevation of boiling-points, show that there are very decided differences ‹in the degrees of ionization of different acids and bases› in solutions of equivalent concentration. For instance, potassium hydroxide is somewhat more ionized than is barium hydroxide, and decidedly more so than ammonium hydroxide, a fact that can readily be demonstrated by the conductivities of the solutions[136]: