ton". The niston is then reinserted into the barrel of the syringe. A; pressure applied to (or withdrawn from) the hase of the buret-syringe with another larger (10- or 15-cc) syringe is used to move the "free" piston for rapid filling or rinsing (see Fig. 2). A piece of gum rubber tubing fitted over the nose of the largersyringe Berves as the air Gal between the two. The majority of users will find that the most convenient way to hold the buret-adaptor assembly during a titration is with the rine and middle fineers of the dominant hand under and surrou~dingthe flangeof the syringe while the thumb and index fineer turn the bolt. The other hand swirls the " titration vessel. Of course, if a magnetic stirrer is used, twohanded manipulation of the buret assembly is more convenient. The following points should be kept in mind when using these burets: 1. The ldancr must be equipped with a draft shield. The shield
should be highenough toweigh thesyringewiththedispensing needle in place when it is plnred upright (seated 01, its base flanpe) on the balance pan. 2. Perform weighing operations with the adaptor uff the syringe. hlany of these top-loading balances are deixned so that 1-mg readabilitv i~ uovsible only if the total massofthe ihject being weighed is less than 20 or30 g. 3. In scaling down experiments, reduce the volumes of solutions, not their concentrations. Good "readability" of titrant quantities is irrelevant if endpoints are rendered "fuzzy" hy excessive
dilution. Reasonable volumes are &10 mL of "unknown" and 2-4 mL of titrant. Most of the classical volumetric determinations used in educational laboratories can be performed with these burets. Compatible titrants include dilute bases, most oxidants, non-halide acids, and aqueous solutions of most chelating agents. In cases where material incompatibilities might be expected, rather modest changes in procedures will usually permit the use of the syringes. For example, nitric acid should be substituted for hvdrochloric acid in acid-base titrations because the stainlkss steel needle corrodes a t a detectable rate in even 0.1 M HC1. Other conceivable objections to small-scale experiments in general and to the use of these syringes as burets in particular, (e.g., the submilligram changes in mass caused by handling the syringes with normally clean hands) do not, in oractice. cause analvtical errors of the maenitude usuallv accepted as inevitable with conventional volumetric equipment. For examde. vlastic svrinae barrels grip the piston sufficiently tightly
