ANALYTICAL CHEMISTRY
432 dipping into the mercury. The internal diameter of the leg a t the narrowest point is such that the clearance between the glass tube containing the platinum wire and the electrode leg is 1 mm. I n preparing the saturated calomel electrode, mercury is added until the level is above the constricted part of the leg (level B ) ; this level was selected to give the maximum area of contact between the calomel and mercury. The glass tube containing the platinum wire is placed in the mercury, calomel is added to level C, a layer of potassium chloride crystals is placed above the calomel, and the leg is filled to level D with saturated potassium chloride EIOIUtion. The electrode leg is closed with a stopper containing a hole of such diameter that the stopper slides easily over the glass tube containing the platinum wire; a split stopper can conveniently be used.
II
borosilicate glass with standard-taper or ball and socket joints of convenient size, such as those illustrated in Figures 1 and 2. The metal-to-glass connections are generally tungsten wire Xo. 16 B.S. gage in uranium glass, although any suitable glass-metal combination may be used ( 1 , 2 ) . The wire leads, silver-soldered to the
LLLLW 0 I 2 30u
Figure 1
With continued use of the conventional H-cell, the agar plug has a tendency to become loose, permitting solution to seep in betwTeen the plug and the fritted glass disk or forming an open space between the plug and disk. Such behavior may result in an abnormal increase in the resistance of the cell o r contamination of sample and reference electrode solutions. I n order to overcome this difficulty, the diameter of the arm containing the agar plug, A , was enlarged slightly a t its mid-point. TTlen the agar is placed in the arm, a ridge is formed due to the enlarged diameter, which keeps the agar plug in place. A stand for holding the cell is made by boring a hole of diameter equal to the external diameter of the water jacket in a block of wood and cutting the block in half along the long axis. Three rubber bands 0.25 inch (0.6 cm.) wide placed around the water jacket at convenient points serve to cushion the cell in the block. Several such cells have been in operation for the past year.
Figure 1
tungsten, are generally 14- t o 16-gage copper. In Figure 2, the leads emerge through small holes in the top of the adapter. A Xichrome wire of 22 gage, approximately 6 inches long, is soldered to the extreme end of the leads.
ACKNOWLEDGMENT
The authors wish to thank the Btomic Energy Commission for a grant which made the work possible.
Adapters for Introducing Hot Coils into Distillation Flasks for Constancy of Ebullition. Julian Feldman and Peter Pantages, Synthetic Liquid Fuels Branch, Bureau of Mines, Bruceton, Pa. HE distillation of most substances in an efficient laboratory Tcolumn a t atmospheric pressures offers no problem with respect to the maintenance of constant boil-up rate-a requisite for good column performance. Generally, the addition of fresh boiling chips, a t the start of a distillation, is all that is necessary to assure continuous ebullition. However, a t reduced pressures, in a conventional boiling flask, it is difficult to maintain smooth boiling, and in consequence, the operating efficiency of the column decreases. A hot wire coil, immersed near the bottom of the flask and carrying an electric current, has been found to be an effective device for controlling ebullition a t reduced pressures. Pyrolytic decomposition can be minimized through adjustment of the temperature of the resistance element by means of a rheostat or variable transformer. In order to introduce these coils into conventional distillation flasks, the authors have used several kinds of adapters made of
Figure 2
Both adapters serve to connect the flask to the back-pressure manometer. In addition, the side-arm adapter holds a thermowell and may be removed to facilitate introduction of a sample or removal of a residue. These adapters were constructed by F. Joseph Malloy. LITERATURE CITED
(1) Barr, W. E.,and Anhorn, V. J., “Scientific Glass Blowing,” p. 116, Pittsburgh, Pa., Instrument Publishing Co., 1949. (2) Heldman, J. S., “Technique of Glass Manipulation in Scientific Research,” p. 87,New York. Prentice Hall, Inc., 1946.
