Constant Delivery Rate Tifration Device Several constant flow devices for time-based titration have been proposed. The immersed eallausible container devices' are somewhat restricted as to container material and lackine sim-
litk; cspscity of titrant, protected from outside contamination, and can dispense the same over a range of selectable flaw rates for convenient titration of a wide range of solution concentration. Finally, if properly used and cared for, it is capable of producing data of quite acceptable analytical quality. The device is pictured in the figure. A 1-liter plastic reagent bottle serves as the titrant reservoir. I t is connected via a short section wide diameter glass tubing fitted with a stopper t o an ordinary Gooch funnel. A small air access tubing is included in the stopper fitted to the funnel. Aseetion of '/,-in. plastic or rubber tubing leads through apinch clamp t o the flow tip. As titrant is dispensed, the liquid level in the Gooch funnel gradually falls, eventually exposing the lower end of the glass tubing t o the atmosphere. At this point, titrant will flow from the reservoir until the end of the tubing is agein submerged, cutting off the supply of air. Thus, the liquid level in the Gooch funnel, and consequently the effective liquid column height between the funnel and the flow tip is held essentially constant, giving rise to oonstant flow of titrant. Flow tips are prepared from capillary tubing. A length of such tubing is drawn out in a flame. The two halves are separated and the drawn end of one half is gradually shortened until a tip with the desired flow rate is produced as determined empirically by periodic checking of the tip on a buret durinc the shortenine urocess. In this manner. tiDs havine flow rates raneine from a
existed a t the stopper joint. By removing and replacing the reservoir in this manner, it is possible t o avoid d l spillage. The constancy of flow was experimentally confirmed by a volumetric technique. A series of t,welve Zmin titrant deliveries vielded s mean of 15.34 ml with estimated standard deviation of
rate will retain its constancy over several hours. It is also necessary t o keep air bubbles from being trapped anywhere along the length of the device, as such bubbles can seriously impede the flow rete. Precautions must be t&en against plugging of tips by foreign matter. When being prepared, there is a. particular danger of plugging due t o broken shreds of glass. It is recommended that completed tips be copiously flushed from both ends with water and acetone, and acid hardened overnight befareuse. Tips not in use should he stored immersed in dilute acid, while those actually in use should be submerged in distilled water to prevent encrustation of titrant salts. 1
M..
KNUDSON, GEORGEE., AND LANQHUS, DAVID,J. CHEM.EDUC.,48. 613 (1971). VANSWAAG, A N D LOLLEY. R. F.. J. CHEM.EDUC..42.381 (1965).
Volume 49, Number 8, August 1972
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