An Improved Modified Dumas Experiment We have found the use of a modified Dumas bulb apparatus, given in the accompanying figure, improves the classical experiment enough to merit the retention af this historically important experiment.' The use of the apparatus yields precise data with greater ease and less east than the classical apparatus. The bulb is calibrated far student use and is weighed evacuated. A sample of volatile liquid is introduced into the bulb utilizing the pressure difference between the evacuated bulb and the atmosphere. The bulb is attached to the vacuum system using an Ace thread ware adapter (=5017-20) on a port of the vacuum system. The modification is made possible by the availability of greaselessZ vacuum Teflon stopcocks or valves.3 We have found the Ace ~8194.03 and the Sargent S 7 6 9 5 5 - A to be equally satisfactory.
VALVE
FLAS''(
DUMAS ASSEMBLY
HEIGHT= 19 CM
'Daniels. F., e t al., "Experimental Physical Chemistry", 7th Ed., MeGraw-Hill Book Ca., New York, 1970, pp. 4-16. Shoemaker. D. P., and Garland, C. W., "Experiments in Physical Chemistry", 2nd Ed., McGraw-Hill Book Co., New York, 1967, pp. 46-53. Wu, D.T-c., and Peatman, W. B., J. CHEM.EDUC., 51,167 (1974). ZA thin film of stopcock lubricant may be used on the "on ring an the valve seat and the thread adapter without problems. A heat gun may be used to heat the area of the bulb below the valve and any liquid above the valve may he removed using the vacuum. 3Aee Glass, h e . , in their most recent catalog, markets a 250-rnl gas ballwn (5393.08) that is similar to the above item and could be used for this application. Ripon College James W. Beatty Ripon. Wisconsin 54971
Volume 52, Number 6, June 1975 / 395
