A Receiver Unit for the Determination of Lactic Acid.

Abstract

The analytical methods for determination of lactic acid have been greatly improved in the last few years, notably by Clausen 1 ; Friedemann, Cotonio and Shaffer 2 ; Davenport and Davenport 3 ; and Friedemann and Kendall. 4

The receiver unit here described was designed for use with the Friedemann, Cotonio and Shaffer 2 apparatus and procedure. When small amounts of lactic acid are to be determined, better checks have been obtained by this method than by the use of other types of receivers. A marked advantage lies in the fact that its use involves a minimum of dilution of the receiver contents, through simplification of washing. This is important, because the end point of the iodine titration is sharper the lower the volume of liquid titrated.

The receiver consists essentially of a 5/16” × 6” test tube, carrying a 2-hole rubber stopper. Through one of these holes there runs a glass tube, drawn into a capillary as soon as it passes the stopper, and extending to the bottom of the tube. The other hole carries a trap, which leads to the source of suction.

In an analysis each such receiver contains 10 ml. of 1.0% sodium bisulphite. Accordingly the incoming gases are drawn through a column of bisulphite at least 10 cm. high, in the form of a stream of small bubbles. The fineness of these bubbles insures a large ratio of surface area to volume, which favors absorption. If the suction be properly regulated, no liquid will be drawn up into the trap, yet a steady stream of bubbles can be maintained.

At the end of a run the tubes are emptied into 125 ml. pyrex Erlenmeyer flasks, the receiver is washed out twice with 2 ml. of wash water, and the titration is carried out in the usual way.