the U-tube, and valve E may be closed. Back-flushing the column, using the 4may valve, F,is optional. After a short wait, to stabilize the base line, a new sample may be injected. Thi- device has 15-orked quite satisfactorily in the determination of butanols and pentanols in a lubricating oil additive. Over 100 determinationc
n'ere made without any apparent chanqe in calibration factors, It is advisable to calibrate the chromatograph using kno\vvnmixtures of the volatiles in the nonvolatiles, rather than to use the pure volatiles. \Then small amounts of volatiles are to be measured in admixture with large amount< of viscous nonvolatiles, the
volatiles are apparently not completely evolved in the introduction cell, even in the firqt run, in some cases. Hon-ever. when calibration is performed with mi-itures similar in composition to the samples to be analyzed, and the .!-stem iq flushed as described after each run, accurate and reproducible rewlti can be expected.
Circulating Pump and Cell for Electrochemical Studies of Gases Paul
E. Toren,
Central Research Laboratories, Minnesota Mining & Manufacturing Co., St. Paul, Minn.
a study of the reaction- of D some n e d y synthesized compounds, it was necessary to measure the elecURISG
trochemical oxidation-reduction properties of a number of gases in solution. Because only small amounts of material were available for these experiments, i t was not possible to work with a solution saturated by a continuous flow of sample gas. Consequently a closed system requiring only a small amount of sample was devised, enabling measurements to be made using only a fenmilliliters of gas a t pressures as low aq 50 mm. By using a knon-n amount of gas sample in a closed system, it was also possible to make coulometric measurements by recirculating the sample through the electrolysis cell until i t was quantitatively o-iidized or reduced. The cell is illustrated in Figure 1. The standard-taper joint a t the top of the cell is fitted with a n ASCO stirring gland, which will accommodate either the conventional dropping mercury electrode capillary, or 6-mm. glass tubing containing a solid electrode. The bottom connection allows the use of a mercury pool electrode, which may be stirred magnetically or by a mechanical stirrer passed through the opening in the stirring gland. For ex-
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Figure 2. Gas-circulating pump and sample bulb
ploratory work, it is usually convenient to stir magnetically and use the top opening for the dropping mercury electrode, so that current-voltage curves can be recorded periodically during a coulometric oxidation or reduction. The construction of the circulating pump and the sample bulb is illustrated in Figure 2. The all-Teflon and glass pump has only one moving part and no mechanical valves, yet it provides positive circulation of gas through the liquid in the clectrolysis cell. The fit of the piston, its rate of travel in the pump cylinder, and the leakage of gas past the piston are such that a pressure difference of about 1 inch of mater is established during the pump stroke. -1s the piston rises, about 1 inch of liquid is drawn into the lower pumii connection, preventing entry of gas from belon while the cylinder is filling with gas leaking around the piston from above. On the downstroke, the positive pressure below the piston is enough to displace the liquid from the lower connection and force the gas
from the pump cylinder through the liquid in the cell. Since the operating pressure equals only about 1 inch of water, the liquid level in the electrolysis cell should not be more than half a n inch above the lower pump connection. The piston is raised and lowered by an external permanent magnet suspended from the rim of a wheel rotated a t 10 r.p.m. by a small motor., I n use, the apparatus is assembled as sho~vnin Figure 3, with the sample in the sample bulb and the desired electrodes and electrolyte solution in the cell. The system is deaerated by passing nitrogen into the system through the upper stopcock, through the pump cylinder and the solution, and out the lower stopcock. Then the sample is introduced by turning the loner stopcock. Sitrogen is supplied through the upper stopcock to bring the internal pressure of the system to 1 atm. (when the sample is introduced at reduced pressure) before the upper stopcock is turned to complete the circulation loop. The desired electrochemical 011erations can then be carried out in the closed system.
Gns CIRCULATION ELECTROLYSIS CELL i
Figure
3.
Gas-circulating system
