NOVEMBER. 1949
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AUTOMATIC TITRATION DEMONSTRATION WILL 8. DelOACH, IAMESIL. EILANDL, and JAMES G. HARMON' Huntingdon College, Montgomery, Alabama
RECEN the~chemistry Y department of Huntingdon College took part in a Science Open House. For such affairs there are always plenty of displays that can be prepared and interesting demonstrations that can he performed, hut it was felt that interest would be added by having something that would "work" by itselfsomething automatic. It was further felt that something involving colored reagents would be attractive. After considerable experimentation, what was referred to as the "Automatic Titration" apparatus was evolved. The setup was so arranged as to deliver alternately a small amount (five or six drops) of 1N NaOH and of 1 N HzSOa into a one-liter beaker containing 600 or 700 ml. of distilled water plus 2 or 3 ml. of phenolphthalein solution. The contents of the beaker were stirred with a motor stirrer, which is not shown in the diagram. The acid and base were contained in the bottles, A, and were delivered by siphon into the reaction beaker, B. The siphons were alternately opened and closed by having part of each made of rubber tubing so that one could be pulled down and pinched shut, as a t C, while the other was pulled up and held open, m a t D. Positive action was obtained in the closing, and leakage was not a problem. The alternate raising and lowering were brought about by attaching the rubber tubing of the siphons to opposite ends of a rocker that was operated by water power. The rocker consisted of a trough, made of tin from tin cans, about 31 cm. long, 2.5 cm. wide, and 4.5 cm. deep. It was divided into two compartments by a partition across it a t the middle, which partition extended about 4 cm. above the sides. The two end walls were only 3 om. high, thus allowing water to spill out a t the ends. To operate the rocker, i t was placed on a pivot and located under a water faucet so that water could run into one compartment just a t the center partition. When the compartment filled, the rocker would tilt in that direction and some of the water would run over the low end wall. As the rocker tilted, the water from the faucet would begin to run into the other compare ment. When that compartment filled, that side of the Members of the class in Freshman Chemistry.
rocker would be heavier, the rocker would tilt in that direction, and the whole procedure would start over. The rocker was located over a sink to take care of the water that spilled over a t each tilting. Screw clamps were used to control the flow from the siphons. The apparatus worked satisfactorily during three sessions of several hours each, although i t required occasional adjustment. The rate a t which the rocker tilted varied with the rate a t which water flowed into it. Variation of water pressure in the lime sometimes made i t necessary to adjust the faucet. Since the amount of acid and the amount of base delivered each time were only approximately the same, one or the other accumulated on long running of the apparatus, and this required adjustment. An efficient motor-driven stirrer was needed so that each reagent would get thoroughly mixed before the other was added.
