A STUDENT TRANSFERENCE NUMBER APPARATUS H. E. HALLAM University College of Khartoum, Khartoum, Sudan
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shortened before bending a right angle a t B. They are then cut at C, rejoined with rubber tubing, and fitted with clips; these form the cat,hode and anode compartments. Next they are joined by rubber tubing to an ordinary U-tube (or to oue made by bending a suitable piece of glass tubing), which forms the central compartment. The electrodes are prepared by fixing pieces of silver wire into the ends of glass tubing by means of sealing wax or a suitable cement. Electrical contact is made by means of copper wires and a little mercnry. Finally, these electrodes are fitted into the anode and cathode compartments by means of rubber stoppers (Figure 2). The total cost of this home-made apparatus is about one-tenth that for a Hittorf apparatus supplied by a manufacturer. The only drawhack it has compared with the standard Hittorf design is the lack of an outlet from the central chamber. I n actual practire this is not serious as at the end of the experiment the
determination of the transference number of an ion by the Hittorf method is a classical experiment and is included in most laboratory courses in physical chemistry. The most commonly used apparatus is that of Findlay1 and is fully described in all the standard works on practical physical chemi~try.~It must either be obtained a t a price from a supply house or be blown by a glass blower. Simpler, though less elegant, designs have been described3 but a certain amount of glass blowing is reauired to construct them.
The apparatus described below can he made from standard laboratory equipment by performing a few simple bends. The required materials are two onebulb distillation columns, one U-tube, glass and rubber tubing, four screw clips, and silver wire: The distillation columns (Figure 1) are heated a t A and the limbs bent back until a t right angles. With most types of columns these limbs will have to be
' FINDLAY, A,, Chem. News,100,185 (1909); "Practical Phyb i d Chemistly," 7th ed., Longmans, Green, and Co., New York, 1941,p. 188. 2 DANIELS, F., J. K. MATHEWS,AND J. K. WILLIAMS, "EXperimental Physical Chemistry," 4th ed., MeCraw-Hill Book Co., Ine., New York, 1949, p. 172; STEINBACH, 0. F., A N D C. V. XING,"Experiments in Physical Chemistry," American Book Co., New York, 1 9 % ~ .163; LIVING~TON, R., " P ~ Y s Chemical ~~o Experiments," Revised ed., The Mncmillan Co., New York, 1948, p. 190. a COLLINS, E. M., J. CHEM. EDUC., 11,52 (1934).
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clips D and E are closed and the anode and cathode chambers drained. The central compartment is then disconnected with D and E in place, held over the titration flask, and carefully drained by opening the clips. If one is a reasonably good glassblower an 306
JUNE. 1954 outlet tube can be joined to the U-tube, thus producing an exact replica of Findlay's design. The author has found that such an apparatus requires a current of 20 milliamperes for 90 minutes to
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produce a reasonable change in concentration of 0.05 N silver nitrate solution, and that students obtain good results for the transference number of the silver and nitrate ions.
