MODIFICATION of VICTOR MEYER'S APPARATUS H. B. GORDON 306 West 20th Street, New York City
A
LTHOUGH the Victor Meyer method has been in use for many years and a number of modifications have been suggested by Henderson (Z), by MacInnes and Kreiling (3), by Weiser ( 4 ) , and others, no important modification of the rather cumbersome apparatus appears to have been generally accepted. It has been the aim of the writer to devise a procedure whereby apparatus which is normally found in every chemistry laboratory may be adapted, by the chemist with but little skill as a glass-blower, to this important determination. The essentials of the apparatus developed are shown in the accompanying sketch. An Erlenmeyer flask, A, takes the place of the usual inner vessel of the Victor Meyer apparatus. For the sake of clarity the ' various apertures in the stopper of the flask are represented as in a line, thus making the neck of the flask appear abnormally wide. The flask is placed in a suitable outer vessel, B, which may be a large beaker, a tin can, or other suitable container. The mouth of the flask is closed by a rubber stopper, C, which is fitted with a slender test-tube, D, and a gas exit tube, E. The test-tube is also fitted with a stopper, F, which carries a small glass exit tube, G, and two iron wires, H a n d I. These wires may be about 2.5 mm. in diameter. About a centimeter of the lower end of H is bent up horizontal, and the upper end is also bent to form a horizontal handle. The lower end of I is bent into a very small loop, J, which is also horizontal. This wire is also furnished with two other horizontal loops, K and K'. These are shaped like a figure 8, ,one loop of which is around the wire. These loops may be made of several strands of very fine wire, such a s is used in flexible lamp cord. They may thus be moved up or down as desired on I but are tight enough not to slide of their own weight. A similar loop, L, holds the two wires a t a suitable distance apart while
permitting H to be rotated. The small glass tube, G, is bent in the form of an inverted U, and is attached by a short rubber sleeve (not shown) to a similar tube, M, in the flask. A more workmanlike arrangement would be to have the tube M sealed into the side of the test-tube just below the stopper, C, but this would require more skill in glass working than does the arrangement shown. The gas exit tube, E, is connected to the gas buret, N. I n the connecting line i t is convenient to have a three-way stopcock, 0. The flask is supported slightly above the bottom of the outer vessel to permit free circulation of the fluid beneath as well as around it. It is well also to cover the outer vessel with a suitable screen, P. The sample is introduced by means of a capsule like that suggested by Dietz ( I ) . Such a capsule consists of a short piece of small glass tube, drawn down to a capillary a t each end. The stopper, F, is withdrawn from the testtube, the wire, H, is so adjusted that its lower end lies across the wire I a t a point slightly above the terminal loop, J. The capsule containing the sample is then put in place. The finer (and weaker) capillary is passed through the loops K and and K' is drawn down over the upper capillary. The loops K and K' are adjusted to hold the capsule firmly in place. The wires carrying the capsule are then slipped into the testtube and the stopper, F, is pushed into place, taking care that the rubber sleeve makes a secure union between the glass tubes G and M. After all excess air has been driven out and the stopcock has been turned to connect the flask and buret, the handle of the wire H is moved through a horizontal arc, causing the lower end of the wire to describe a corresponding arc. The capillary end of the capsule is thus broken, the sample is liberated and immediutely vaporized. The heavy vapor from the sample is formed a t the bottom of the test-tube and forces air from the top of the test-tube through the tube M to the bottom of the flask, driving air from the top of the flask to the gas buret. On account of the rapidity of the vaporization of the sample some of the air expelled is likely to be lost if it is received in a simple gas-measuring tube. The use of a gas buret is therefore essential. Obviously the outer vessel may be filled with either steam or liquid. If with liquid it need not boil if it is kept a t the same temperature before and after the vaporization of the sample. The question naturally arises whether any of the
vapor of the sample is driven out of the flask. To test this the method used by MacInnes and Kreiling (3) was employed. Test paper containing potassium iodide and starch was placed in the delivery tube near the stopcock, and a sample of bromine weighing 0.1350 g. was introduced and vaporized in the usual way. The test paper was not affected and but a trace of bromine vapor could be observed in the flask outside the test-tube. An obvious simplification of the apparatus is the omission of the test-tube, D, and the glass tubes, G and M. The wires in this case are inserted in the stopper of the flask and this is withdrawn for introduction of the charge. By another simplification the tubes G and M are omitted and the test-tube is replaced by a glass tube open a t both ends and long enough to extend from near the bottom of thc flask above the covering screen, P, but only large enough to admit the capsule easily. The end of the capsule is broken off, and the capsule, broken end first, is dropped into the tube, whose upper end is immediately closed by suitable means. Vaporization by this procedure is of course gradual, and if desired the buret may be replaced by a simple gas-measuring tube. Experience indicates that with .the lirst of these simplifications some vapor is likely to be expelled from the apparatus with consequent high values for molecular weights. However, results are as accurate as required in most cases. The writer's students have appeared to obtain a t least as good results with both
simplified forms of equipment as with the usual form of Victor Meyer apparatus, and have of course found the manipulation much simpler. It is necessary, however, to exercise some care to avoid burning by the steam evolved except in using the second simplification. Loading the sample into the capsule deserves some mention. The most natural way to accomplish this purpose is to place one end of the capsule in a small beaker of the liquid under investigation and to suck with the lips a t the other end. The method is fairly satisfactory but may result in pricking the lips or in drawing some of the liquid into the mouth. A better method is to use a small rubber tube, one end of which is closed by a glass bead. Near this bead a hole is made in the tube wall by means of a pin. One end of the capsule is inserted in the pin-hole, the other end is placed in the liquid under investigation, and gentle suction is applied a t the open end of the rubber tube. Pressure on the rubber tube by the thumb and finger helps to regulate the amount of liquid drawn into the capsule and in its retention while the capsule is lifted from the liquid. The ends of the capsule are sealed by a small flame. LITERATURE CITED
DIETZ,A,, J. CHEM. EDUC., 9, 20964 (1932). HENDERSON, W. E., J. Am. Cham. Soc., 34, 553 (1912). (3) MACINNES, D. A. AND KREILING,R. G., ibid., 39, 2350 (1) (2)
1,017, ,LO",.
(4)
WEISER,H., I . Phys. Chem., 20, 532 (1916)
