A sensitive method for measuring carbon dioxide.

Abstract

The most sensitive method hitherto used for measuring the carbon dioxide output of tissues in vitro is the method of Tashiro, 1 depending upon the detection of a crystal of barium carbonate in a solution of barium hydroxide under the microscope. It was found that 1 × 10^-7 of a gram of carbon dioxide gave a visible precipitate in 10 minutes. An unknown amount of carbon dioxide was measured by rinding such a dilution that a visible precipitate was just formed in 10 minutes. This method has not been found useful in practice in the hands of others.

The next most sensitive method is the indicator method of Osterhout, 2 which in the hands of Parker 3 has been found adequate for the detection of 1 × 10^-6 grams. It takes, however, 20 × 10^-6 grams to produce the standard color change in the indicator. If this change takes place in 20 minutes, Parker finds himself able to detect a perceptible color change after 1 minute, i. e., from the effect of 1 × 10^-6 grams.

At the Cleveland meeting of the Federation, December, 1925, the writer demonstrated a carbon dioxide method based upon measurements of the conductivity of barium hydroxide, with which it is possible to detect 1 × 10^-7 of a gram of carbon dioxide. The method was designed for the estimation of the carbon dioxide output from a stimulated nerve. Owing to an unavoidable delay in completing the experiments on nerves it has seemed advisable, in response to requests from other workers, to publish a brief description of the method, which is not new in principle. It was pointed out to me at Cleveland that it had been used by Spoehr 4 for relatively large amounts of CO₂.