Reflux-Distillation Adapter
venting vapor loss. Dow-Corning Silicone stopcock grease was found to be an acceptable lubricant.
FRANK KIPNIS AND JOHN ORNFELT Research Laboratory, American Home Foods, Znc., Morris Plains, iV. J .
LITERATURE CITED
(1)
Fieser, “Experiments in Organic Chemistry,” 2nd ed., pp. 322-3, Boston, D. C. Heath & Co., 1941.
RECEIVED February 26, 1947.
T IS frequently necessary, in the organic chemistry laboratory, I t o reflux a mixture, and then remove all or a portion of the solvent by distillation. This sequence of operations may occur during crystallization procedures or a t the conclusion of a reaction. Most of the equipment designed to accomplish these operations is unduly cumbersome and intricate. The apparatus described by Fieser (I) is convenient and efficient, but rather fragile, and requires precision glass blowing to give an acceptable implement.
Multiple Dropping Mercury Electrode THOMAS DE VRIES AND WRI. S. BARNHART Purdue C-nizersity, Lufayette, Znd. hIULTIPLE dropping mercury electrode has been designed
A and used in this laboraory to facilitate the polarographic
determination of very lory concentrations of reducible substances. The diffusion current produced when one dropping mercury electrode is used is proportional to the ionic concentration of the element which is being reduced. If four (or more) dropping electrodes are connected in parallel, the current flowing should be four times as great for a given ionic concentration; conversely, the smallest ionic concentration which can be determined polarographically is now lowered by a factor of four.
aa -
I
W
Figure 1
Figure 2
The multiple dropping mercury electrode was constructed from a 60-em. length of 10-mm. glass tubing. The lower end was sealed to a 20-mm. bulb from which protruded four arms of 6-mm. tubing (Figure 1). These arms were bent to form a cluster of tubes in line with the rest of the column. A short length of Corning “marine barometer tubing” was attached to each tube with rubber connectors.
It has been shown ( I ) that a direct comparison of different elecThe trodes is possible by means of the equation i d = krn2’3 t”8. product m2/3 t 1 / 6 for a single dropping mercury electrode was determined as 1.97 mg.2/3sec.-’/z The sum of the products for the multiple electrode was equal to 7.63 mg.2/3sec.-1/2 A solution of lead (11) ion (1 mg.) in 1 S potassium chloride (50 ml.) was polarographed with the single electrode and again with the four dropping electrodes a t the same instrument sensitivity. The polarographic waves are shown in Figure 2. The single electrode wave is 16 mm. high while the multiple electrode wave for the same solution is 62 mm. high. Corrections were made for the residual current. This agrees well with the 61.9-mm. value calculated from the capillary constants of the respective electrodes. The above data show that the concept of multiplying a polarographic diffusion current by using more than one dropping mercury electrode is sound.
Figure 1
The accompanying diagram indicates an adapter (manufactured to specification by the Scientific Glass Apparatus Co., Bloomfield, N. J.) which has been used successfully for reflux and subsequent distillation without the necessity for interruption of operation. The apparatus is rugged, is rather simple to fabricate, and the dimensions are not too critical except a t the ring seal. Much less working space is required than in the conventional distillation unit. The joint and side tube a t the receiver are not essential, but have been found convenient for distillation under anhydrous conditions. Standard interjoint flasks and condensers may be used with this adapter. The stopcock is closed when refluxing is required. For distillation, the stopcock is adjusted so that a portion of liquid distillate is always present on the “hot” side of the stopcock, thus pre-
LITERATURE CITED
(1) Kolthoff and Lingane. “Polarography,” p. 60, Kew York, Interscience Publishers, 1941.
RECEIVED February 7 , 1947.
934
