The Hydrogen-Ion Concentration of Natural Waters, I. the Relation OfpH To The Pressure Of Carbon Dioxide

ABSTRACT The evidence that the variations which occur in the hydrogen-ion concentration of a natural water have any direct effect on the inhabitants living under natural conditions is scanty and not very convincing. On the other hand, there is good evidence to show that many animals are tolerant of the changes in hydrogen-ion concentration of their native habitat. These variations can hardly be related to distribution, epidemics of conjugation and the like, for these are known to occur at very different values of the hydrogen-ion concentration. Occasionally it can be shown that the variations are sufficiently extreme to cause the total extinction of certain species, but this will only be in very small pools. It is true, of course, that profound changes can be produced in biological reactions in the laboratory by altering the hydrogen-ion concentration of the medium in which the reaction is taking place, but these changes are nearly always greatly in excess of the natural changes occurring in the normal environment. It appears to me that the real importance of the measurement of the hydrogen-ion concentration of a natural water is that it can be used as an accurate measure of the carbon dioxide produced by the animals and of the photosynthetic activity of the plants. But to use the measure of the hydrogen-ion for this purpose we must know something of the underlying principles involved in the measurement and must not merely be content with matching the colour produced by the addition of an indicator with the colour of a buffer solution prepared by a rule of thumb method.