The Calibration of the Osterhout Respiratory Apparatus for Absolute Quantities of Carbon Dioxide

In the course of a piece of work on the amount of carbon dioxide produced by sea anemones it was found desirable to use the respiratory apparatus devised by Osterhout (1918), and as it was necessary in this work to determine the absolute quantity of carbon dioxide eliminated by these animals, an attempt was made to calibrate this apparatus for such determinations. The method finally adopted seems to be of enough general importance to justify a brief statement of it. The Osterhout apparatus consists of a closed system in which the air is made to circulate by means of a pump. The air passes from a chamber, in which the organism is confined and in which consequently the carbon dioxide is produced, either directly to a glass tube containing an indicator in solution or indirectly to this tube through a U-tube filled with fragments of sodium hydroxide. In the direct course the air containing the carbon dioxide is forced to bubble through the indicator solution, thus causing it to change its tint. In the indirect course the air is relieved of its carbon dioxide by contact with the sodium hydroxide, and, after purification, it is bubbled through the indicator thus washing out the contained carbon dioxide and bringing the indicator back to its original color. From the tube containing the indicator the air returns by a direct course through the pump to the chamber in which the organism is confined. A figure of the apparatus is given by Osterhout (1918). In taking readings with this apparatus the time in seconds required for the indicator to change from one tint to another as compared with standard solutions of known pH value is recorded and the rate