NOVEMBER 15, 1940
ANlLYTICAL E D I T I O S
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2 per cent. Further refinements leading to a greater sensi-
Acknowledgment
tivity of the voltmeter could increase to almost any desired value the accuracy with which the field strength could be estimated. Switch B is used to reverse the polarity of the electrodes in the electrophoresis cell without affecting any other part of the circuit. B y occasionally comparing the reading a t D when first X then r is connected into the grid circuit, variations in the applied voltage a t C can be made to maintain constant the value of E during the course of the measurement of migration velocity. The electrophoretic properties of particles suspended in alcohols of specific conductivity approximating 10-8 mho, and of particles suspended in aqueous solutions of specific conductivity of the order of mho, have been measured with equal facility with this apparatus.
The author is pleased to acknowledge the aid of Ralph Hossfeld in the construction of the flat part of the electrophoresis cell.
Literature Cited (1) Abramson, H. A,, Ann. A:. Y . Acad. Sci., 39, 121-16 (1939). (2) Abramson, H. A , “Electrokinetic Phenomena”, page 257, S e w York, Chemical Catalog Co., 193.1. (3) Abramson, H. A , , J . Gen. Physiol., 12, 469 (1929). (4) Bull, H. B., J . Phys. Chem., 39, 577 (1935). (5) Komagata, S., Researches Electrot&. Lab. T u k ~ 348 , (1933). (6) Moyer, L. S., J . Bact., 31, 531 (1935). (7) Northrup, J. H., and Kunita, XI.. J . Gen. Physiol., 7 , 729 (1925). (8) Smoluchowski, XI., in Graetz “Handbuch der Elektriaitit und des Magnetismus”, Vol. 11, p. 36G, Leipzig, B a r t h , 1921. PAPERNo. 1822, Scientific Journal Series, 2Iiiinesota Agricultural Experiment Station.
Microhydrogenation Apparatus ARTHUR N. PRATER AND A . J. HAAGEN-SRIIT California Institute of Technology, Pasadena, Calif.
A
LONG with the development of general microanalytical
procedures for organic compounds, i t has been necessary t o produce more specialized methods. One such method that has assumed great importance in structure determination is the quantitative measurement of the amount of hydrogen consumed in a microhydrogenation. For investigations on plant hormones and other physiologically active substances in the authors’ laboratories i t became necessary to construct a n apparatus for microhydrogenation. There have been several devices of this type described by various investigators (2-6, 8, 9) which have one or more of the following objectionable features: The apparatus must be operated in a
sensitiue thermostat, incomplete temperature compensation is provided, and a large, fragile, glass coil or d lubricated ground joint is used to connect the reaction and measuring systems. The apparatus described here is in part a combination of the desirable features of the earlier designs referred to above, and is so constructed that the entire reaction and measuring system is shaken as a unit, eliminating the necessity of having ground joints which must be able to rotate freely and yet be absolutely gas-tight. The apparatus has been in use for the past year, and has given satisfactory results on a number of compounds. Complete temperature compensation is pro-
FIGURE 1. TOPVIEW OF APPARATUS
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INDUSTRIAL AND ENGINEERING CHEhPISTRl-
e d T O PLATlNlZ E D ASBEST05
FIGURE2 . SCALE DRAWINGOF REACTION AND HYDROGESPCRIPYING SYSTEhfS
vided by having two completely symmetrical systems connected so t h a t one serves as the reaction system and the other as the compensator. Both systems carry a 4-ml. and a 50-ml. buret, extending the usefulness of the apparatus to small-scale preparative work on a quantitative basis. I n cases where the temperature compensation is not necessary, two determinations can be run simultaneously, effecting a considerable saving of time. Description of Apparatus The apparatus consists of three main units: the hydrogenpurifying system, the reaction and measuring system, and the vacuum system. Figure 1 gives a top view showing the relative positions of the three units. A scale drawing of the reaction and hydrogen-purifying systems is shown in Figure 2. The rigid framework consists of 2.5-cm. (1-inch), seven-ply wood bolted together with right-angle strap iron. The reaction and measuring system is carried on a panel of 1.25-cm. (0.5-inch) ply wood, and is pivoted on an axis centered along 3A and 3B. The center portion of the panel is cut away to allow room for the flasks, heater, etc. The axle is a 1.25-cm. (0.5-inch) steel rod held to the rigid framework by two bronzebushed adjustable shaft hangers and to the swinging panel by bronze bushings. This entire unit is rocked by an eccentric driven by a sewing machine motor. A speed of 75 t o 150 strokes per minute through a 15" arc provides thorough mixing in the reaction flasks. Connections to the hydrogen-purifying system and the vacuum system are made through ground joints 3A and 3B, respectively. For convenience in quickly connecting the apparatus and to reduce breakage, these joints are located in the axis of rotation. When the system has been Elled with hydrogen, however, the connecting pieces, 2A and 2B, are removed, since they are no longer needed. The reaction and measuring system is symmetrical along the line connecting stopcocks 6 and 8. Each half of this symmetrical unit has a 50-ml. and a 4ml. (0.01-ml. divisions) buret, a reaction flask with a 24/40 ground joint connecting to the apparatus, and a side stopper for introducing the
sample (5). The two symmetrical halves are connected by the two three-way stopcocks, 6 and 8. Two ground joints, 5A and 5B, are necessary for flexibility in assembling and cleaning. Except for the burets, stopcocks 9A and 9B, and the reaction flasks, the entire react'ion and measuring system is constructed out of 1-mm. capillary tubing and 1-mm. capillary stopcocks. Joints 5 8 and 5B are so constructed from capillary tubing that no large pocket is formed within the gas space. The mercury leveling bulbs are adjustable along steel rods a&ed to the stationary framework, The hydrogen purifying system is similar t o that previously described ( 6 ) . It consists of a heated tube of platinized asbestos, two bubbler tubes of sodium plumbite solution, and two drying tubes filled with anhydrous magnesium perchlorate. The stopcock, 1, isolates the purifying system when not in use. The hydrogen is taken from a cylinder through a reducing valve set at 5- to 10-em. of mercury (1 or 2 pounds') pressure. The vacuum system may consist simply of an aspirator or, more elaborately, of a high-vacuum pump, cooled traps, and a McLeod gage. The latter is useful in detecting leaks in the apparatus, although the former simpler arrangement is satisfactory. In these laboratories a portable vacuum unit is used which can be connected to the system by the ground joint Jvhen an analysis is t o be run.
Reagents 4 n y of the highly purified solvents customarily used in hydrogenations may be employed. Platinic oxide (1) and platinum black have been used as catalysts.
Cleaning and Assembling Apparatus The entire apparatus is cleaned thoroughly and dried. The ground joints and all the stopcocks except Xo. 8 are greased,with a good quality degassed stopcock grease. The glassware 1s assembled and clamped on the shaking board. The flasks are attached by wing-nut screw clamps. It is important that the clamps be carefully padded with felt to prevent breakage. Joints 5 A and 5 B are held together by springs or strong rubber bands.
NOVEMBER 15, 1940
The burets are filled with purified, redistilled mercury. Stopcock 8 is lubricated with an oil-insoluble glycerol-mannitol-dextrin mixture (7). The manometer is filled by sucking butyl phthalate through stopcock 8. For ease in reading, the butyl phthalate may be colored with Sudan red.
Testing the Apparatus For convenience and clarity in presenting the details of the manipulation of the apparatus, the positions of the stopcocks are illustrated in Figure 3 and are designated by Roman numerals.
-1
II:
m
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ANALYTICAL EDITION
E
'ZL
41:
m
FIGURE 3. POSITIONS OF STOPCOCKS T h e efficiency of the temperature compensation can best be ,checked by bringing the system to equilibrium at room temperature, and then with stopcock 6 in position VII, transferring the whole apparatus to a cold room near 0 " C. Any differences in volume in the tn-o sides \Till be shown by the butyl phthalate manometer. These initial differences can be eliminated bv softening one of the reaction flasks in the flame and altering its volume slightly. Since these volume differences are small, i t is also possible to correct for them by determining the volume correction factor and compensating for this with the burets in the compensation system. Before each determination, especially if the apparatus has been out of service for some time, i t is advisable to test for leaks by taking a volume reading and then allowing the apparatus t o stand for awhile with the leveling bulbs either raised or lowered to provide pressure or suction. N o difficulty has been experienced with leaks when the joints and stopcocks are well lubricated.
been reduced the mercury level is again adjusted with stopcock 8 in position 111, so that the butyl phthalate manometer shows no pressure difference. If a large amount of catalyst is being used in the hydrogenation it is advisable first t o reduce it with the 50-ml. buret connected and finish the reduction with the microburet, since the microburet gives a more accurate reading with small volume differences. If necessary the microburet can be refilled from either of the 50-ml. burets a t this stage. However, if stopcock 6 is turned to position V it is again necessary t o adjust the left mercury leveling bulb to atmospheric pressure and record the temperature and barometric pressure. After the buret reading has been taken, with stopcock 6 in position VI1 and 8 in position I, the sample is introduced by turning the ground plug, and the shaking mechanism is started. The course of t'he hydrogenation can be readily followed by momentarily stopping the apparatus and taking a quick volume reading. The reaction time raries considerably with the type of compound and the amount and activity of the catalyst' used. The reaction is considered complete when separate buret readings agree before and after a 30-minute shaking period. For the final reading the apparatus is allowed to stand for an hour untouched. During the manipulations, it is advisable to avoid touching the burets or the reaction flasks. Substances which require a n elevated temperature for hydrogenabion may be accommodated by clamping a small electric heater under the reaction flask. This is accomplished simply with the aid of a n angle-iron clamp attached to the back side of the shaking board. As this is only infrequently used, it is generally removed to lower the inertia of the mechanism. K h e n an elevated temperature is used in the reaction i t is necessary to allow a longer time for temperature equalization before taking the final reading. The apparatus may be purchased from the Kational Technical Laboratories, 820 Mission St., South Pasadena, Calif. Table I contains data on substances used as standards. Platinic oxide was used as the catalyst and purified glacial acetic acid as the solvent.
Operating the Apparatus
TABLE I. STAKDARDS
The flasks are carefully cleaned and dried. Both flasks are charged with catalyst and solvent, and the platinum sample tube containing the weighed substance is carefully hung on the hook. The flasks are clamped in place, strong rubber bands being used to hold the joints tight. With stopcock 8 at I and 6 at I11 (open to the air) the mercury in the burets is run up to 7 A and 7B. Care must be exercised to prevent the mercury -from running over into the reaction flasks. .Stopcocks 7 A and 7 B are turned through 45" to positions I and 11, respectively, shutting off the burets; stopcock 6 is turned to position V; stopcocks 4A and 4B are turned to I V and VI, respectively; and the system is evacuated. The vacuum is interrupted by turning 4B to V, purified hydrogen is admitted through 1, and the mercury is lowered in the burets, filling them with hydrogen. The hydrogen supply is then shut off at 1, the system is evacuated by turning stopcock 4B to VI, and the mercury is again run up to stopcocks 7 8 and 7B. The entire evacuating and flushing procedure is repeated four times to remove all the air and fill the entire system with pure hydrogen. The connecting links 2A and 2B are then removed. While the apparatus viill function with them in place, their removal obviates the danger of breakage during the prolonged shaking to follow. Stopcock 9B is then turned to 11, so as to shut off the righthand mercury leveling bulb, and the left mercury leveling bulb is adjusted so that the gas in the apparatus is a t atmospheric pressure. The temperature is read on a thermometer hung close to the apparatus, and the barometric pressure is noted. Stopcock 6 is then turned t o VII, 8 is turned to I11 so as t o actuate the manometer, and 7 A and 9-4 are turned to I V to connect only the microburet. Similarly 7B is turned t o position VI. The microburet is read and shaking started. For safety, the left leveling bulb is kept at just about the same height as the mercury in the buret', and manometer stopcock 8 is kept closed (position I) except during the actual volume reading. It is important that no air be admitted to the system through stopcocks 4A, 4B, or 6, while a determination is in progress. .Ifter the catalyst has
Hydro- Barogen metric CataAbPreslyst- sorbed sure Mm. MQ. Cc. HQ 20 742 2.04 12.9 2.67 745 7.7 742 1 56 12.3 742 7.87
Substance
Sample
Maleic acid Maleic acid 1Ialeic acid Cinnamicacid
9.700 12.633 7.341 11.737
MQ.
Tempera- Double Bond8 ture Found Theory
(7. 24 22.5 24 22
0.98 1.00 0.99 4.00
1.00 1.00 1.00 4.00
On analysis of a fully saturated compound, shaking at room temperature followed b y prolonged shaking at 90" C. yielded a final volume reading agreeing within 0.01 ml. with the original value, establishing the reliability of the apparatus when used a t higher temperatures.
Acknowledgment The authors wish to thank J. G. Kirchner for valuable advice and suggestions, and Henry Lanz for assistance in the analyses.
Literature Cited (1) Xdams, Voorhees, and Shriner, "Organic Syntheses", Collective Vol. I, p. 452, New York, John Wiley & Sons, 1932. (2) €3. Foresti', Ann. chim. applicata., 26, 207 (1936). (3) Bretschneider and Burger, Chem. Fabrik, 1937, 124-7. (4) Hyde and Sherp, J . Am. Chem. Soc., 52, 3359 (1930). (5) Jackson and Jones, J. Chem. Soc., 1936, 895. (6) Kuhn and Moller, Angew. chem., 47, 145 (1934). (7) hlelocke and Fredrich, J . A m . Chern. Soc., 54, 3264 (1932). ( 8 ) Slotta and Blanke, J . prakt. Chem., 143, 3 (1935). (9) Smith, J.. J . Biol. C'hem., 96, 35 (1932).
