Analysis of Ether-Air Mixtures by Thermal Conductivity Method.

For the purpose of rapid determination of ether concentration in ether-air mixtures we have found the thermal conductivity method of gas analysis satisfactory. Since the heat conductivity of ether vapor is only about one half as great as is that of air, the admixture of ether vapor with air decreases the loss of heat from the wire and causes its temperature to rise. The consequent increase of electrical resistance of the wire is readily determined and, if the apparatus is calibrated, the change of resistance is a measure of the ether concentration.

The apparatus used in this investigation consisted of a rectangular brass block 14×4×2 cm. in size through which 2 parallel holes 1 cm. in diameter were bored longitudinally. In each cell a platinum wire 0.005 cm. in diameter was suspended axially from plugs closing the ends, and heated by a current of 0.2 ampere. The gas was introduced through lateral tubes close to the ends of the cells. The calibration was effected by means of several ether-air mixtures of known concentration. These were made up by breaking, in a closed flask of known volume, a capillary tube containing a weighed quantity of ether. The mean experimental error of the determination was about 5% with concentrations between 0.3% and 1.3%. It is probably considerably less than this with mixtures of the usual anesthetic strength (6%-8%).

For concentrations of less than about 5% the resistance of the wire was approximately proportional to the concentration. When, however, larger concentrations were used proportionality no longer obtained. With concentrations greater than 10% the apparent heat conductivity began to increase until with mixtures of about 30% it was equal to that of the air Mixtures stronger than 30% had a cooling effect greater than that of air.