CELL FOR ELECTROMETRIC MICROTITRATIONS VICTOR C. GARBARINI' and SIDNEY HEILVEIL' Nichols Laboratories, New York University, New Yolk
IT IS difficult to place all the elements required for microtitrations in a cell of a satisfactory size. The cell described eliminates most of the difficulties, is extremely simple to construct, and easy to use. Construction is obvious from the diagram supplied. A 19/25 male joint ( A ) is passed through one hole of a 3-hole rubber stopper placed in a bottle of any convenient size. The bulb on the female portion of the joint is blown out into a cup-like receptacle (B). A tube with a platinum wire sealed into the end is passed through another hole in the stopper so that electrical contact with the mercury a t the bottom of the bottle can be achieved (C). In the third hole, a piece of glass tubing with an aspirator bulb on one end and a vent is placed (D). In use, the male joint is first coated on the inside with a silicone preparation such as Beckman "Desicote" as the lubricant. The tube is then filled with an agar salt bridge. A saturated calomel electrode system is placed in the bottle. For titration, the female cup is placed on the male joint and the solution to be titrated is placed therein. Any suitable microburet (F) can be used for the titration. The agar plug in the bottom of the male joint serves as a salt bridge for the saturated calomel reference electrode. The indicator electrode used is a vibrating platinum electrode (E) which also serves as a stirrer. After the titration is complete, the cup is re-
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' Present address: Esso Research and Engineering c;., Linden, New Jersey. Present address: General Electric Company, Rocket Engine Section, Cincinnati 15, Ohio.
moved and by stopping the vent and squeezing the aspirator bulb, the agar plug is raised about an eighth of an inch. A razor blade is used to slice the plug off level with the end of the tube. The cup is replaced and the assembly is now ready for another titration. Caution must he used when applying pressure since the agar plug may sometimes stick slightly and then spurt out. The above apparatus has been used successfully for amperometric titrations of bromate-arsenate systems using initial solution volumes of the order of 0.05 ml.
JOURNAL OF CHEMICAL EDUCATION
