G. Wilson Drake
University of Houston Houston, Texas
Modified Victor Meyer Apparatus
The determination of vapor density by the Victor Meyer method has long been a useful determination taught in the physical chemistry laboratory. As usually performed, the experiment is rather cumbersome since it involves making and fding sample bulblets, heating a rather large steam jacketed vessel and measuring a displaced volume of air. A student who had had a course in gas chromatography, casually remarked that the sample should be injected with a syringe. The following apparatus was constructed to use a microsyringe for sample introduction and, incidentally, to reduce the size of the equipment and the time required for a determination. Description of Apparatus. The apparatus consists of a Pyrex glass tube ( A ) about 40 cm long and 3.5 om in diameter (see Fig. 1). A slight enlargement ( B ) is
Semi-micro Viclor Meyer apporalur.
blown on the lower end to receive the liquid which is refluxed to supply a constant temperature jacket. A 15 cm length of 2 cm tubing (C) has lengths of 8 mm tubing sealed to each end. The lower length is bent a t a right angle and cut to fit inside the jacket. The upper 8 mm tube is secured in the top of the jacket by a ring seal. The lower one is then sealed through The author acknowledges with pleasure the assistance of Arthur P. Ingram and Harry K. Montgomery, Jr., both of the University of Houston, and Kenneth M. Richards, Brevard Junior College, Cocoa, Florida.
606
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Journal of Chemical Education
the wall of the jacket and the opening (D) is tooled to accept a 6 mm silicone puncture type seal or septum. A side-arm (E) to receive a small reflux condenser is provided near the top of the instrument. The portion of the instrument between the septum and the condenser side-arm is insulated with a layer of aluminum foil and a layer of loose asbestos cloth. The upper, or exit, tube (F) of the Victor Meyer apparatus is joined by means of a 0.5 mm bore capillary (G) to the gas buret (H). Short lengths of rubber tubing are used to make the connections. The gas buret has a capacity of 10 ml and may be made conveniently from a 10 nd graduated pipet. The leveling bulb (I)is a length of glass tubing of about the same diameter as the pipet. The confining liquid is mercury. Operation of the Apparatus. A few milliliters of ethylene glycol are added through the condenser side-arm and heated to rapid reflux. The delivery tube (G) is detached from the gas buret (H), and an aspirator is attached to draw air through the hot apparatus. The delivery tube is replaced, the mercury is leveled, and a silicone seal is pushed into the opening (D). A very small fumlel made of glass tubing is inserted in the hole in the seal, This enables one to thrust the needle quickly through the septum even though the area around the septum is quite hot. A small syringe needle may be introduced through the septum so that atmospheric pressure is re-established inside the appamtus. A microsyringe is filled to the desired volume with sample, the usual precautions being taken to elimiuate all air bubbles. The end of the needle is closed hy thrusting it into a small piece of a silicone plastic and the syringe is weighed. Next, the empty needle is withdrawn from the septum at D and the gas buret is read. Then the silicone plug is removed from the syringe needle, the plunger is withdrawn enough to empty the needle back into the syringe body. The needle is thrust through the septum and the sample injected. The leveling bulb is lowered to the correct level. The plunger of the syringe should he withdrawn again to empty the liquid remaining in the needle back into the syringe. The needle is then plugged again and reweighed; the amount of sample vaporized is found by difference. Sample vapor volume is read from the buret. This detailed procedure for introducing the sample is necessary to be sure that all the sample which leaves the syringe-and only that-is introduced inside the apparatus.
The table illustrates results obtained. In the series of determinations on methylene chloride determinations were rejected out of 13, since deviations were four times the average deviation.
first two the The
Summary of Results
Mol. rpt. Number of cases 11 10 -.
10 10
Sub stance CHICIS
CCI. CSH~ ~
CCL
Formula weight
expenmental
Precision
84.94 1.5XR4 - ~ -78.11 153.84
85.2 154.8 78.1 153.7
85.2 z t 0 . 5 154.8 + 2 . 9 78.1 + 0 . 4 153.7 + 0 . 8
next three determinations are composed of 10 consecutive cases, each with no rejections. The precision of the measurements, indicated in the last column, seems to be as good as the precision of weighing the sample and of measuring the displaced air. A typical sample weighed 0.0413 g as measured on a Type H5 Mettler balance. A typical volume measured 6.43 ml as read in a buret graduated to 0.1 rnl. I n the first two sets of determinations the apparatus was insulated only with aluminum foil. Asbestos insulation was addkd for the other two sets of determinations.
Volume 40, Number 1 1 , November 1963
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