J. H. Robertson
University of Tennessee Knoxville
An Improved Victor Meyer Vapor Density Apparatus
In the Victor Meyer method of determining vapor density, a weighed sample of the liquid is vaporized and the volume of air displaced from the vaporization unit is measured under the prevailing conditions of temperature and pressure in the room. The method requires a design of apparatus which will prevent the passage of the vapor from the heated vaporization unit to the unheated parts of the apparatus where condensation would take place. For this reason the vaporization unit in the ordinary form of the apparatus is made quite long. The apparatus is rather cumbersome, and it does not efficiently accomplish its purpose of retaining the vapor within the heated unit. To obtain compactness or to achieve greater security from vapor condensation, various modifications have been made. In the Weiserl design, the distance the vapor must travel before escaping from the heated unit is increased by sealing a J-shaped delivery tube through the bottom of the vaporization bulb, the short end extending almost to its top and the long end extending up through the outer heating jacket. This design, which has appeared in various manuals, has two objectionable features: (1) the volume of the vaporization bulb is largely dead space which makes it necessary to insert an accessory tube to sweep out vapors between successive determinations. (2) the long leverage on the exit end of the tube makes it very susceptible to breakage a t the bottom seal when assembling or disassembling the apparatus. I n the Hicks-Bruunz apparatus, a 10-mm tube through which the sample is introduced projects downward through a series of bulbs forming annular spaces along the seals between the bulbs. Escaping vapor or air expands successively through these &all spaces giving a steady flow of air into the measuring buret. Escape of vapor from the jacketed part of the apparatus, although favored by the turbulence of flow through the small annular spaces, is prevented by the large capacity of the bulbs which total approximately 1 liter. The Hicks-Rmun apparatus was designed for a special study of the molecular weight of petroleum constituents by the method of limiting density. In the MacInnes and Kreiling3 design, which is conveniently homemade, compactness is achieved by means of a central vaporization tube with open lower end extending down into and almost to the bottom of Presented hefan the Division of Chemical Education at the Southeastern Regional Meeting of the American Chemical Society. Gainesvillo, Florida, December, 1958. WEISER, H. B., J . P h y ~ Chem., . 20, 532 (1916). HICKS-BRUUN, M. M., U.S. BUT.Standards J . Research, 5, 5 i 5 (1930). MACINNES, D. A,, 39, 2350 (1917).
AND
KREILINCI, R. G.,
152 / Journal of Chemicol.Educofion
J . Am. Chem. Soc.,
the inner, jacketed compartment,. The sample bulb is fastened a t the top of this central tube so that when the sample bulb is crushed vapor must pass downward through the central tnbe, then upward around it to the top before reaching the unjacketed part of the apparatus. The design of the Victor Meyer apparatus described here is shown in the photograph. The jacketed exit tnbe from the vaporization chamber is 2 m (6'/1 ft) in length. From the point a t which it leaves the vaporization chamber near the top, the tube is wound downward around the vaporization chamber and then upward in the helical space between the downward windings. It is then sealed through the wall bf the outside heating jacket. The mouth of the vaporization chamber is also sealed through the outer jacket and flanged for fitting with a stopper. A mouth for condenser connection is also sealed into the outer jacket.
Victor Meyer apparatus showing coiled exit tube from vaporization chamber. h o k i n g device with perforated discs is shown.
To minimize convection currents, the vaporization chamber is divided into several compartments by means of perforated metal discs. These are mounted on a central shaft which may conveniently function also a,s part of the breaking device. The perforations in the discs are for the purpose of diminishing the turbulence of flow through the annular spaces between the wall of the chamber and the rims of the discs. Such discs, but without perforations, were first used by the author more
than twenty-five years ago. They are recommended in certain laboratory manual^.^ The breaking device is an adaptation of the MacInnes and Kreiling device which is here extended almost to the bottom of the vaporization chamber and on which the sample bulb is merely suspended and free to fall when crushed because it is desired to vaporize the liquid a t the bottom of the chamber. The advantage of the present design are: (1) compactness-the overall length is only about 33 cm; (2) almost complete freedom from the danger of vapor condensation; (3) durability-the apparatus is constructed of Pyrex and the helical delivery tube is free to expand and contract without developing serious &rain; (4) r DANIELS,F., MATHEWS, J. H., WILLIAMS,J. W., BENDER, P., AND ALBERTY,R. A,, "Experimental Physicd Chemistry," 5th ed., McGraw-Hill Book Co., Inc., New York, 1956, p. 10.
convenience of the mouth for condenser connectionthis is especially desirable when boiling liquids other than water are used. Typical student results are given in the table. Routine vapor density determinations by students using the design of apparatus described have been less subjected to erratic errors than with the ordinary form of the apparatus. Illustrative Student Data Using Ethylandine (B.P. a s Boiling Liquid
M
Substance
=
204'C)
gRT/PV
Beneene (78.11) Chloroform (119.39) Water (18.02) Toluene (92.14) Aoetone (58.08) Diethvl ether 174.12)
Volume 37, Number 3, March 1960
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