2.00 centimeters = 0.45 g, etc.) The mass of water in grams, and hence the volume in milliliters, can be plotted versus measured distance in centimeters, as shown in Figure 2. Experimental data for a Charles' Law determination using this procedure are shown in the table, where the measured gas bubble level at each temperature was converted to an actual volume using the calibration plot of Figure 2. Linear regression analysis of the data points extrapolated to zero volume (Fig. 3) yields a value for absolute zero of 276 'C, in excellent agreement with the accepted value. In this particular run, data were taken only while the oil was heating but additional data points also could be collected while the system is cooling back to ambient conditions. One of the most useful aspects of this procedure is that once the bubble tube is prepared and calibrated, it can be used repeatedly to collect volume/temperature data without disturbing the equipment setup.
Microscale Ninhydrin Test Applied to Solid-Phase Peptide Synthesis Lluis Vilaseca and Eduard Bardaji University of Girona PI. Hospital 6 1707, Girona, Spain
The reaction of ninhydrins has been used extensively for the detection of free primary amino m u ~ sIts . use as a test during the sGihes;s of peptides ria solid-phase methodolow ( 1 , 2 ) makes it &I efficient tool f~f-~e@tide chemists to ensure complete formation of each peptide bond (3).It is also a useful tool for assessing reaction yields when carrying out difficult couplings. Here we report a microscale modification of the ninhydrin test, which allows the use of very small portions of peptidyl-resins and reagents, employing melting point tubes. The general procedure is illustrated in the figure. First, a small portion of washed peptidyl-resin is taken with one end of an open melting point tube. One drop of ninhy-
Volume 72 Number 5 May 1995
A99
the microscale laboratory 3. Hadge, R. S.; Memifield, R. B.Aml. Biachem. 1975,65,241-272, and references "fed themin.
d
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Small-Scale Experiments Involving Gas Evolution H. Brouwer
resin as, d
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w
end
seal clean end f i r s t
I
Few grains of resin are loaded onto a mening point tube (a),the ninhydtyn reagent is taken by capillarity through the same end (b) and the clean unused end is sealed with a flame (c).Once cooled down, the mixture is dropped down and the other end sealed (d).The test tube is ready to be placed on a preheated oven at 110 "C (e). drin reagent is placed on a clean and dry watch glass and, employing the same end used to load the resin onto the melting .. noint . tube. a nortion of the reagent is taken by capillarity. Both resin and reagent are allowed to flow to the middle of the tube. With the mixture in this position, the unused clean end of the melting point tuhe is sealed with a flame. Once this end has cooled down, the mixture is pushed to the bottom of the tube by tapping or dropping the tuhe gently. With the mixture on the bottom of the tube, the other end is sealed. The nynhydrin test can be carried out as usual on the sealed tube. In a n oven or sand bath preheated to 100-110°C less than 1minis needed for the reaction to be developed. This sealed tube teehru&e has several advantagesover the use of open containers (e.g., vials). Because the sealed tube prevents evaporation, the mlor remains stable for hours, improving the test reliability and allowing more leisurely evaluktion. -huther, the mi&oscale nature of the test saves reagents and synthetic material, increases the ease of the procedure, and reduces toxic vapors in the laboratory. Literature Cited 1.Schmberg,A; Singcr, E. ntmhedmn lslB,34,12861288. 2. Memifield. R B. J.Am. Chem Sae. 198%85,214W2154. A100
Journal of Chemical Education
Redeemer College Ancaster, ON L9K 1J4. Canada Quantitative gas experiments offer the means to illustrate a variety of chemical concepts, such as stoichiometry and kinetics. Such experiments often are limited by the lack of appropriate and inexpensive volume-measuring devices. The apparatus described below provides a means of measuring volume changes in small-scale experiments, as illustrated by the accompanying experiments. The design of the apparatus is shown in the diagram (Fig. 1).A 10-mL syringe is fitted to a two-hole rubber stopper (#I)using a piece of Tygon tubing (id. 118in.) and glass tubing (0.d. 4 mm).' A second glass tube, to serve as a manometer, is shaped from a 25-cm length of glass tubing (0.d. 4 mm) as in the diagram and inserted in the other hole of the stopper. A small amount of water is added to this tube: care is taken not to trap air bubbles in the water column. This is most readily acc~mplishedby holding the tube nearly horizontal and addim water with a dropper or syringe. f i e stopper is then attacked to the reaction iessel ra small Erlenmeyer flask or a test tube). When this apparatusis used for measuring gas volumes, the reactants are placed in the vessel (solutions are measured conveniently using a 5-mL syringe), the stopper assembly is attached, and the level of the water in the manometer tube is adjusted to equalize the pressure inside and outside the vessel by withdrawing the syringe piston. The initial volume is then recorded. As the reaction proceeds, the piston is slowly withdrawn to maintain the water level in the manometer. The apparatus also may be constructed in a more flexible manner using thin (about 2-mm o.d.1 polyethylene tubing. Two 10-cm lengths are inserted through a one-hole stopper and sealed with hot melt glue. The syringe is connected to 'Inserting a needle fitted to the syringe into a one-holestopper was tied, but it was difficult to obtain an airtight seal.
T
1 r 10 mL Syringe
Tygon Tubing Glass Tubing
(with water)
Erlenmeyer Flask (ortesttube)
Figure 1. Diagram of gas-measuring apparatus,
