Manometric System for Volumetric G a s Analyzers AMOS R. ANDERSON Houdaille-Hershey Corporation, Decatur,
THE
use of nonscientific personnel in operation of the socalled precision model volumetric gas analyzer has presented many difficulties in this laboratory, which has to analyze several hundred gas samples a week. The two most troublesome are blowing out or sucking in of manometer fluid by the operator, and the development of a leak in the middle of an analysis.
111.
For the first manometer, a design was worked out which roughly equalizes the gas pressure before operung the sensitive manometer to the system, gives a continuous visual indication of the pressure within the system, and compensates partially any abnormal pressure or vacuum developed in the system during the analysis. This manometer is built into the water jacket and makes use of the gas buret for one arm of the U. The other arm is a small-diameter glass tube which connects to the gas buret at the base by means of a small glass Y. The system is shown in Figure 1 as it was built into the regular buret manometer-compensator assembly. The left arm, A , of the built-in manometer is constructed of 6and 8-mm. tubing, the base being 8-mm. tubing to correspond with the gas buret outlet. The main body of the arm is of 6-mm. tubing and has a small ground-glass, ball check valve, B , sealed to the top. The over-all length of this tube for a 77.5-cm. (31inch) water jacket, C, is 100 cm. (40 inches) and it contains approximately 12 ml. of mercury when completely fijled. The connecting Y-tube a t the base is of 8-mm. tubing and has 2.5cm. (1-inch) arms to facilitate good seals with the rubber connecting tubing. The other parts of the assembly are self-explanatory. The compensator tube, F , w w placed in the abnormal position shown, for clarity on the two-dimensional drawing, and normally occurs directly behind the gas buret, E. This manometer system (1) eliminates the guesswork involved in equalizing the mercury levels before opening the sensitive manometer to the system, thus preventing one of the causes of blowout or suckin of manometer fluid; (2) it helps to compensate for any abnormal pressure or vacuum which may be exerted on the system, thereby decreasing leaks; and (3) i t gives the analyst a continuous visual indication of the pressure within the system throughout the entire analysis. All these factors contribute toward faster and more consistently reliable analyses. The system makes cleaning and reassembling of the buret unit somewhat more difficult; however, used on several analyeers in this laboratory for more than a year, it has helped to prevent errors.
Figure 1. Improved Manometric System as Installed in a Regular Gas-Measuring Unit
Lubricant Reservoir for Stirrer Shaft The first difficulty is frequent with beginners but occasionally happens during fast operation to the most experienced gas analyst. With standard apparatus this is usually due to difficulty in obtaining accurate equalization of the mercury levels in the leveling bulb and the gas buret, particularly in the lower portions of the system, or failure to close the manometer stopcock before starting the flow of gas. The second difficulty is usually due to excess positive or negative pressure in the system. These difficulties and the time lost in dismantling, cleaning, and reassembling apparatus, refilling the manometer, and repeating analyses, prompted the design of the system described below. Nearly all commercial models of volumetric gas analyzers contain one ordinary U-type manometer with one arm attached to the compensating tube and the other to the manifold or t o the buret itself. The system described here consists of two manometers, one for rough preliminary equalizing of the gas pressure and the second for sensitive and accurate final pressure balance. For the latter, the manometer contained in the original apparatus serves very well when filled with a slightly acidified aqueous solution.
JOHN H. ROBSON Department of Chemistry, University of California, Los Angeles, Calif.
I
N ORDER to avoid liquid-sealed stirrers, the author has been using stirrers of the type described by Fieser (1). The stirrer bearing is equipped with a 2-em. section of rubber tubing which projects above the end of the bearing and makes a tight fit on the stirrer shaft. This rubber bearing requires frequent lubrication to prevent heating and consequent impairment of the seal. A very satisfactory lubricant reservoir can be made by cutting off the closed end of a medicine dropper bulb and fitting the decapitated bulb over the rubber bearing. This device has been found serviceable over long periods of time, requiring only a few drops of glycerol or heavy mineral oil once a day. LITERATURE CITED
(1) Fieser, L. F., “Experiments in Organic Chemistry”, p. 310, Boston, D. C. Heath & Co., 1941.
’IC
