A Simple Colorimetric Method for Field Determinations of the Carbon Dioxide Tension and Free Carbon Dioxide, Bicarbonates and Carbonates in Solution in Natural Waters. I. A Theoretical Discussion

Abstract

The most troublesome factors for the biologist to measure accurately, or even to estimate, are carbon dioxide tension and free carbon dioxide, bicarbonates and carbonates in solution in natural waters. In order to obtain accurate knowledge of the conditions of natural waters these factors must be determined in the field, unless all necessary precautions are taken during the collection and preservation of samples to avoid any change in the factors from those in the field. This is extremely difficult and verges upon impossibility, as will be shown in later discussion. The importance of determining these factors as they exist in the field should not be minimized. One needs only to consult any good text-book on physiology to be convinced of the importance of the carbon dioxide partial pressure of the alveolar air of lung-breathing animals in maintaining a constant alkalinity of the blood: in short, the importance, in the respiratory function, of the carbon dioxide tension of the blood of animals possessing a hemoglobin system of transporting oxygen from the respiratory organs to the tissues of the body. The study of the effect of the carbon dioxide partial pressure of alveolar air on the physiology of respiration of lung-breathing animals has been an important field of investigation. On the other hand, the investigation of the effect of a rapid variation of the carbon dioxide tension of the medium surrounding gill-breathing animals has been much neglected. Doubtless the reason for this neglect is the great difficulty in determining accurately the carbon dioxide tension of water, and the lack of a simple method by which it can be determined rapidly. When the literature is examined it is found that the methods in vogue for the determination of carbon dioxide tension, free carbon dioxide, bicarbonates and carbonates, must be employed with caution. Johnston ('i6) has given an excellent criticism of the standard methods employed in water analysis. The law of mass action has been applied, and formulae have been developed, for the purpose of calculating the values of one or more of the factors from the known values of other factors, that is, we are here dealing