MODIFIED HEMPEL GAS ANALYSIS APPARATUS ASSEMBLEDfrom EVERYDAY LABORATORY APPARATUS A. R. HERSHBERGER Western Union College, LeMars, Iowa
T
HE NECESSITY arose for the author to analyze flue gases in making some heating plant tests. No apparatus was a t hand, so a modification of the Hempel apparatus was constructed from everyday equipment which may he found in any laboratory. The modified Hempel apparatus was very successful for the purpose intended. It was then applied to student use for the analysis and study of various gases such as automobile exhaust, air in rooms, cigarette smoke, etc. After learning to use the apparatus, students rarely made errors in analysis greater than one or two tenths of one per cent. The procedure with this apparatus is identical with that in which standard apparatus is used, with the exception of a detail or two which are given below. APPARATUS
The Gas Buret. This consisted of an inverted, 100-ml. buret with a three-way stopcock and side lilling tube as shown in Figure 1, A. A simple, pinch-clamp buret could have
been used, but the manipulation of gases was made easier with the three-way stopcock. The lower, open end of the buret was fitted with a one-hole rubber stopper, and a 250-ml. aspirator bottle with about three and one-half feet of rnbber tubing was connected to this stopper to regulate the level of the liquid in the buret. The buret bad to be calibrated to the zero point B, Figure 1, in order to calculate the per cent. by volume.
Modified Hempel Gas Absorption Pipet. The modified pipet is shown in Figure 1 and includes all parts but the buret, A. C and H are screw clamps on a / , inch, thin-walled rubber tubing and are used to
regulate the level of the solution in the flasks and to keep out air when not in use. D is l-mm. capillary tubing, although standard 'Ir-inch glass tubing could be used. This capillary tubing must not extend below the lower surface of stopper E. E and K are standard, two-hole rnbber stoppers fitted to the flasks. F and I are 125-ml. Erlenmeyer Pyrex flasks. Absorption takes place in F, and I holds the solution displaced from F by the gas sample. The diagram shows the measured gas sample from the buret transferred to flask F in position for absorption of a constituent. G is a rubber tubing connection and J is ordinary '14-inch glass tubing.
Gas Sampling Tube or Bottle. A 250-ml. or a 500-ml. pear-shaped separatory funnel was used in storing gas samples for short periods or for collecting samples a t a remote place from the analysis apparatus. The diagram, Figure 2, shows a separatory funnel sample tube in the act of transferring a sample of gas to buret A as indicated by the arrows. As the gas is drawn out of B, water from beaker D displaces the gas. This water is previously acidulated with about two per cent. H 8 0 4 and saturated with the type of gas used, as is that in the buret also. Instead of using beaker D, a second separatory funnel could be used clamped in an upright position, with the lower end connected to tube C. The beaker set-up is simpler, however. To obtain a sample of gas in B, i t is used in the ordinary way by connecting a glass or other tube to the top of the funnel in place of the buret as shown. With B fnll of water and the tube a t the top inserted in the gas to be sampled, the lower stopcock is opened and the gas is siphoned into the funnel by displacement. PROCEDURE
Except for the modifications noted hereafter the procedure for this modified apparatus is identical with that used for standard apparatus. Because the standard procedure and details of mixing the absorption solutions are available in practically all of the standard handbooks of quantitative analysis, they will not be described here.
Exceptions to Standard Procedure. 1. In filling the absorption pipet flasks, the stoppers
E and K of Figure 1must not be allowed to become wet with alkaline solutions, for they will then become slippery and will cause trouble. 2. A standard pipet bulb is conical a t the top, while the stopper E, Figure 1, is flat. For this reason one should avoid leaving any bubbles of gas in the flask
when the sample is transferred over to the buret for measurement. 3. Absorption of the gas is carried out by shaking only flask F, Figure 1, about a horizontal axis C-G, instead of shaking the entire pipet as is done when the standard pipet is used.
