AN IMPROVED METHOD OF INTRODUCING THE SAMPLE INTO A VICTOR MEYER VAPORIZATION CHAMBER
A number of modifications of the original Victor Meyer vapor-density apparatus have been suggested in an effort to increase the accuracy and speed of pera at ion,'.^.^,' but the student in the physical chemistry laboratory still experiences considerable difficulty in making molecular-weight determinations by this method. The preparation of the sample and its introduction into the vaporization chamber is one of the chief difficulties. Two methods are in common use: (1) the sample is either sealed in a thinwalled glass bulb and dropped to the bottom of the vaporization chamber where it is broken by impact, or (2) placed in a small glass-stoppered weighing bottle and dropped onto a mercury or asbestos cushion. If the first method is used the student is often required t6 blow his own bulbs, and, unless he has had experience a t glass-blowing, he will waste a number of hours in obtaining bulbs of the proper wall thickness. Even after he has acquired sufficient skill to blow the bulbs many may break too soon, and it also often happens that the bulb fails to break when released. Should this happen much time is wasted in removing it, for it may break in a future determination. If the weighing bottle is used it must be removed after each determination to avoid breaking it when the next sample is introduced. Since it is not sealed some of the liquid may escape before the proper time, and if the stopper is put in too tightly it may not blow out when it should. The cost of the glass-stoppered weighing bottles is a further disadvantage. MacInnes and IQeilinga and Chapin4 have suggested methods whereby a bent capillary may be broken from the capsule. Their methods have some advantages, but it is sometimes hard to bend the capillary so that it will fit into the set-up. The method here described overcomes some of the disadvantages of the other methods. The cross-section of the arrangement is shown in Figure 1. The top of the inner jacket of the Victor Meyer apparatus is fitted with a rubber stopper, through which extends the glass tube A of about 4 mm. inner diameter. B is a glass rod that will slide easily through A . At the top is a rubber tube Ct which is tightly wired to the glass tube A, and its upper
* Senior in chemistry at the University of Toledo. t Z / m n black-gum mbber tubing serves well. PAITERSON, "A Simple Form of Release for Victor Meyer's Vapor-Density Apparatus." Chem. Nms, 97, 73 (1908); Chem. AbsB., 2, 1217 (May 10, 1908). GIL. "Modification of Victor Meyer's Vapor-Density Apparatus," J, Chem Soc., 102, 537 (1912); Chem. Abstr., 7, 1117 (Apr. 10, 1913). MncINms AND RBBILING, "An Improved Victor Meyer Vapor-Density Apparatus," J.Am. Chem. Soc., 39,2350-4 (Nov., 1917). T~nnpm."A Modified Victor Meyer Apparatus," J. Ind. Eng. Ckenz.. 4, 684 (Sept., 1912). J
2096
VOL. 9, NO. 12
VAPORIZATION CHAMBER
2097
end is clamped securely with a screw clamp to prevent leakage. D* is a short piece of heavy-walled tubing which resists stretching to any great extent, and with an inner diameter a little less than a piece of common glass tubing. Into D fits the capsule E containing the liquid of which the molecular weight is to be determined. This tube is shown in more detail in Figure 2, and is made by beating glass tubing in a narrow flame, and then quickly drawing it out to a fine capillary. A whole string of these can be made from a piece of glass tubing in less time than it would take to blow one bulb. The tube may be easily filled by applying a gentle suction a t one end until the proper amount of liquid has entered, and then it is sealed a t both ends. If the liquid is very volatile it must be filled by dis. placement of air. The arrangement is fitted into the apparatus, and when it has Stopper come to a constant temperature the glass rod is pushed against the upper capillary, breaking it, and then with a second push the tube falls to the bottom breaking the capillary a t the other end. With both ends open the liquid easily and rapidly distils out. The rubber tube D must hold the capsule E tightly enough to permit the breaking of the one capillary, and the tube C is of such a size to allow FIGURE1 the passage of the glass rod, a t the same time holding it tightly enough to prevent its falling to the bottom when the capsule is released.
* S / ~ a " heavy-walled red rubber tubing should be used.
2098
JOURNAL OF CHEMICAL EDUCATION
DECEMBER, 1932
Summary A method which makes the Victor Meyer determination more rapid and
less liable to mishap is described. The tube described for holding the sample bas the advantage over the usual thin glass bulb in its ease of preparation and filling, and in the certainty of its breaking. Its advantage over the weighing bottle lies in theimpossibility of premature vaporization of the liquid, for i t is sealed a t both ends. The tubes may be stored in cotton packing until needed. The whole arrangement is compact, easily made, and easily manipulated, and has proved to be successful.
