can be used for a reference cell or a standard cell 2 em. in diameter can be used in conjunction with a metal disk diaphragm having a 4-mm. aperture.
Figure 1. device
Disassembled monitoring
The tendency of the pen to dig through the paper a t slow chart speeds is eliminated by recording intermittently in a manner that consists of a closure of the “master” switch for a short period a t predetermined intervals. The “power,” “slit,” (‘pen;’ “chart,” and “lamp” switches remain on during the entire column run, while contact from the master switch is made by a program timer of the general class used for reflux ratio control. The most usual operating conditions were 7 seconds of recording a t 6minute intervals, with a chart speed of 1 inch per minute. Under these conditions continuous column operation has been satisfactorily maintained for 5 days. The spectrophotometer timer and fraction collector were usually synchronized to give three observations per time-controlled fraction with a column flow rate of 1 ml. per minute. 4UAL OPERATION
_”..-__
A.. operation, the switches are counected to operate in the regular manner. The apparatus is assembled as shown in Figure 2. The sample is loaded into the funnel and a t the same time drawn through the cell with the syringe. A solution with an absorbance of 2 can he washed out completely with 4 to 5 ml. of solvent nr replaced by the same volume of new solution. I
Figure 2. Assembled monitoring device
clear aperture (8). The ends are threaded to hold the quartz disks, D, 11 mm. in diameter and 2 mm. thick. The cell is held to block B with two springs, E. The holes in the top of the cell are tapered to fit a 5/20 standardtaper inner joint. The inlet and outlet tubes, F, of the cell are made of 2-mm. capillary tubing joined to a 5/20 inner joint. The tip of the ground joint is cut off so that it will not extend into the light beam through the cell. The tubes are positioned and held in the cell with the aid of two springs, E, attached to the ears on the tubes &s shown in Figure 2. The tubes are aligned in the plate by means of screws and washers as shown in Figure 1. The stopcock is 2-mm. bore. The funnel has a capacity of 5 to 10 ml., and the syringe a capacity of 10 ml. CONTINUOUS MONlTORlNG
To operate the device for continuously monitoring a column effluent, the funnel stopcock and syringe shown in Figure 2 are removed. The outlet of the column is attached to a tube, F, entering the Teflon cell. An outlet tube leading to a fraction cutter or other collector is a b tached to the other tube F. Filling the cell with alcohol aids in preventing airbubble formation. Another Teflon cell 862
ANALYTICAL CHEMISTRY
LITERATURE CITED
J. E., Boucher, E. G., Robinson, A. E., Wiebe, A. K., ANAL. CHEM. 27, 1888 (1955). Irk, P. L., Rosenfels, R. S., Hanahan, KD. F., Ibid., 19,355 (1947).
(1) Kenyon, W. C., McCarley,
(’)
MENTIONof products by commercial name does not imply recommendation by the Department of Agriculture over others of a similar nature not mentioned.
Warburg Manometer Flask for Increased Sensitivity in Ethylene Determinations Harlan K. Pratt, University of California, Davis, Calif., and Curt W. Greiner, Greiner Glassblowing Laboratory, 3604 East Medford St., Lor Angeler 63, Calif.
of ethylene by the method of Young, Pratt, and Biale (3). In this strictly chemical determination, the flask volume is critical only in its effect on the accuracy of the physical measurement. By using flasks with the small-
Figure 1. Manometer flask
est possible gas space aboye a given volume of liquid, sensitivity IS increased because the amount of gas released in an analysis gives a larger pressure reading in the constant-volume, variable-pressure manometric system. The flask here depicted (Greiner Catalog No. 23-500) is conical, with a 17/20 standard-taper ground joint, and with elass . . . a~ o~~ ~ nartition dividing the bodv of the flask into^ two equar compare ments. Each side of the flask will accommodate 3 ml. of sample or reagent. The hooks are placed so that shaking IS in a plane a t a-right angle to the partition; if shaking is parallel to the partition, premature mixing is likely. Total volumes of the flasks average about 10 ml., and the vessel constants of one set averaged 0.66, compared to 1.80 for the two-chamber vessels previously used or to standard 15-ml. Warburg vessels. ~~
~~
~~
Warburg manometers can be read to the nearest 0.5 mm. Assuming that the total available volume of one sample of mercuric perchlorate solution is 20 ml., and 3-ml. aliquots are taken for analysis (S), a minimum of 120 pl. of ethylene could be determined with the standard vessels, or 44 pl. with the type described (allowing *5% as satisfactory accuracy). Further increase in sensitivity might he obtained using the hydraulic leverage principle recently described by Burk and Hobby (1). The special flask of Stanley and Tracewell (8)does not appear to meet the desired standard of high fluid volume coupled with low gas volume. LITERATURE CITED
Burk, D., Hobby, G., Science 120, 640-8 (1954). Stanley, R. G., Tracewell, T., Ibid., 122.7R-7 _._, .. . (1955). ...,. ~~
A
m m o v m flask has been designed for the manometric determination
N
Young, R. E., Pratt, H. K., Bide, J. B., ANAL.G E M .24,551-5 (1952).
