V O L U M E 20, N O . 11, N O V E M B E R 1 9 4 8
1109
A
B
microscope (Figure 7). The exact nature of this structure is not clear, yet it was observed repeatedly under these conditions and under no other conditions. However, when precipitated with an alcoholic solution of dipethylglyoxime, the crystah are smooth-edged and appear to consist of tightly packed bundles of thinner needles (Figure 8). It han been reported (1) that palladium dimethylglyoxime appears under the optical microscope to possess a bdderlike structure due to twinning. The reason for that report on the hasis of these electron micrographs is not clear, although the lumps of Figure 6 possibly account for it. Bismuth Dimethylgljoxime. Bismuth forms au insoluble compound with dimethylglyoxime in ammoniacal solution. . T h e precipitate appears yellow t o white, depending upon the conditions of precipitation (primarily ammonium ion coucentratiou), and has not been found satisfactory for a gravimetric determination (8). Figure 9 illustrates that the appearance of the dimethylglyoxime precipitate under the electron microscope is very similm to that of bismuth oxychloride or bismuth oxynitrate, depending upon which anion is present at the time of precipitation. Varying the ammonia concentration merely altered the particle size and had no appreciable effect upon general form. The precipitation of bismuth dimethylglyoxime must involve, then, some form of a coprecipitation with a basic bismuth salt. (It has been suggested that Figure 9, A and C, may represent the &NOture of this substance after meltine under the electron
C
1)
be valid, as each of the micrographs is typical of a large number of visual ohservations of material prepared in the D, Bj manner stated. It is unlikely, however, that the material shown is a melted structure, inasmuch as bismuth oxychloride melts at “red heat” only and could hardly he completely melted prior to visual observation of the particles after the sample isinserted in the instrument andelectron beam turned on.)
Figure 9. B i s m u t h Precipitates A, RiOCI; B, RiONOa: C, Bi dimsthylglgmims from Rich
aolufioo;
dimethylglyoxime from Bi(NOa), solution
cipitate, Pd(CIH,0sN2)8, from dilute mineral acid solutions: the precipitate is generally formed by adding solid crystal., of the reagent (a). When crystalline dimethylglyoxime was added t o a test drop of a palladium solution acidified with hydrochloric acid, the crystal8 formed appeared much different than when an alcoholic solution of dimethylglyoxime N&Sused. When formed from a IO-¶ M palladium solution, the crystals are smoothedged near the ends but very rough in the middle (Figure 6). This roughness must be inherent in the particles and not due to partial melting of the specimen under electron bombardment in the microscope, as it appears only on the thickest portion of the needles. From 10;’ M palladium solution the crystals possess a peculiar segmented structure, as observed in the electron
LITERATURE CITED
E. M.,and Mason. C. W..“Handbook of Chemical Mioroscopy.” 2nd ed.. New York. John Wiley & Sons. 1938. (2) Diehl, H., “ApplicationsoftheDiolimesto AnalytioalChemistry,” Columbus. Ohio. G. F. Smith Chemical Co.. 1940. (3) Fischer. R. B.. J . Chern. Education. 24,484 (1947). (4)Gulbransen, E. A,. Phelps. R. T., and Langer, A,, IND. ENG C n m . , ANAL.Eo.,17,646 (1945). (1) Chamot.
R E C E ~ Y EDecember D 29, 1947. Presented before One-Day Technical Cooferenoe sponsored b y Chicago Seotion, Axmnrcm C a m r c ~ bS O C L E T and ~, American Association for the Advanoement of Science. Chiaapo, Ill., December 26, 1947.
High Precision Ultramicroburet ROGER GILMONT, The EmiZ Greiner Co., New York, N. Y. An u l t r a m i c r o b u r e t based o n the displacement principle is presented. A precision plunger enters a m e r c u r y reservoir t h r o u g h a r u b b e r gasket sealed in a stuffingbox a n d the linear motion of the plunger is measured by a dial micmmeter gage that reads directly in volumetric units.
T
HE simplest microburet is an adaptation of the ordinary this type of microburet is reduced, difficulty of manipulation _ _ ’ buret in which the comparatively wide-bore glass tubing is and drainage errors became magnified. replaced hy caDillarv tubine. and orohably dates as far back as Newer tvnes of microburets reduce the disadvrtntrtees. ”. the macroburet itself. It heen used-for liquids and gases One employs a mercury reservoir in which the mercury is Blacet and Leighton ( f ) , Dustman Lochte by Ormont (M), forced into the calibrated crtpiUaw tube by means of a piston, and and H~~~~~ Standen and F ~ , , ~ ~ and s~~~~~~~ measurement is made at the mercury-titrating solution interface ($42, Clark and H e m n c e (% Grahame ($1, Ogg et al. (17), [Rebberg (H), andLinderstrplm-LangandHolter (is)].Another and Hawes and Skavinski (11). As the size of the capillary in forces the mercury into the calibrated capillary by raising the
has
~
(9a,
(n,
ANALYTICAL CHEMISTRY
1110 reservoir with a rack and pinion arrangement as described by Conway (3) and McFarlane (16). Sometimes contact between the mercury and titrating solution cannot be tolerated, and modifications of the Rehberg buret maintain an air column or thread between the mercury and solution [ Linderstr$m-Lang and Holter (14) and Cunningham et al. (d)]. The use of the air threads eliminates the effectiveness of the mercury in reducing drainage errors. Drainage errors may be completely eliminated by reading the volume displacement on a calibrated micrometer screw which motivates a precision piston that enters the mercury reservoir through a gasket seal. The idea for this was conceived by Emich (8), whose hand-made instrument was capable of 0.000004ml. sensitivity. Dusing (6) improved the Emich model by using a standard manufactured micrometer head. hlercury was eliminated by employing a syringe activated by a micrometer screw described by Trevan (27) and Dean and Fetcher ( 5 ) ,but only a t a sacrifice of sensitivity. Hadfield (10) used a precisionbore glass tubing and a precision-fitting piston motivated by a micrometer screw to produce a very sensitive and precise syringe type of micrometer buret. Titus and Gray (26) describe one which employs mercury as an intermediary fluid between titrating solution and piston. Scholander (21, 22) describes a microburet built around an ordinary shop micrometer similar to the original Emich type. A very elaborate microburet based on the same principle as the Emich buret is described by Keston et al. ( l a ) ,Rosebury and van Heyningen (20), and Wyatt (28).
Use of the Scholander microburet has led to design of a new buret. A direct-reading dial micrometer gage replaces the micrometer screw gage and the fiber gasket is replaced by a rubber gasket in a simple stuffing box. The dial gage simplifies reading, so that it may be made more rapidly and with Iess danger of gross errors, and the rubber gasket eliminates most of the leakage of the fiber gasket xith extensive use. The stuffing box design reduces dimensional changes in the rubber, so that accuracy is not affected. This instrument may readily be applied to the micromeasurement of gases as well as liquids-for example in microrespirometers. It may also be modified with little trouble for automatic measurement, as the screw can be turned by a motor vihose motion can be controlled by suitable electrical contacts. THEORY
The volume of liquid displaced by the piston is given by
v = -r D42 L
(1)
where V = volume displaced, D = diameter of piston, arid L = length of travel into reservoir.
Figure 1. ,Microburet Titration Assembly
I
IT
e
,4
r - - - - - - - - - -1
1
V O L U M E 2 0 , NO. 1 1 , N O V E M B E R 1 9 4 8 The fractional error in volume is obtained by differentiating and dividing through by Equation 1,
For a buret constructed to give a total displacement of 100 cu. mm. with a 25.4-mm. (1-inch) travel dial micrometer gage (from Equation 1, the diameter of the rod would be 2.239 mm. or 0.08815 inch), the error in volume is about O.l%, if the gage is accurate to 0.0005 inch and the piston diameter is kept to a tolerance of 0.0002 inch. This accuracy may be improved by using a more accurate gage and by holding the piston diameter within a closer tolerance; however, the accuracy of each part should be comparable, since improvement in one of the parts would be wasted unless the other part were improved to the same extent. The limit of sensitivity of this buret is considerably lower than 0.000004 ml. for the early Emich (8) model. Scholander and Evans (23) have constructed one ivith a wire plunger sensitive to 0.00000007 ml. and corresponding to a micrometer reading estimated to 0.001 nini. Because of the ultrasensitivity of this microburet, the effect of temperature may appear to be excessive, especially if a large reservoir is used; however, if the volume of the reservoir is kept to a minimum approaching that of its total titrating capacity, changes due to temperature will be of the same percentage order of magnitude as those on a macroscale. Assuming a reservoir of minimum volume and taking an average value of 2 X lo-‘ per O C. for the cubical coefficient of thermal expansion of mercury or ivater, the error in volume due to temperature is 0.04% per C., so that a full degree change in temperature during titration results in an error that is not greater than the maximum accuracy usually attainable with thi. buret. DESCRIPTIOY OF 4 P P 4 R 4 T U S
The details of construction for a 0.1-nil. total displacement microburet are shown in Figure 1. The internal diameter of the glass reservoir should be a b closr to that of the plunger as possible, to minimize temperature effects and dimensional changes in the rubber gasket; ordinary 3-mm. Pyrex capillary tubing was found adequate. Silicone rubber is an ideal material for the gasket, effecting a perfect seal without binding. A collar not shown in the diagram may be attached to the end of the screw in contact with the gage, so that back motion of the screw will carry the gage with it. This collar may be made detachable, so that the gage can also be worked by hand when desired, as in filling or changing solutions. Clamps to hold test tubes, bubbling tubes for air stirring, and a milk-white glass may be attached to the vertical rod on the stand. ASSEMBLY AYD FILLING
The glass tube reservoir i y placed between the two projections of the base with the rubber gaskets against the closed and open ends of the reservoir. A little dab of silicone grease may be placed on the surfaces in contact in order to make a vacuum seal. All e w e s grease is wiped off. The reservoir is carefully aligned and sufficient pressure applied on the anvil screw to make a tight seal. The unit is completely filled by use of vacuum. A small test tube with a side arm is connected to the buret tip through a rubber stopper. The side arm ie connected to the source of a good vacuum through a three-way stopcock, so that the test tube may be connected to the vacuum or air. Mercury, preferably of C.P. grade, is placed in the tube so that the tip of the buret is a little above the surface of the mercury when the tube ia vertical. The vacuum is connected to the tube by turning the stopcock, and the buret is allowed to be evacuated. Teat for leakage is made by tilting the tube of mercury until the tip of the buret is under the surface of the mercury. Continued bubbling through the mercury indicates a leak which can be eliminated by properly adjusting the pressure on the anvil screw. When a vacuum-tight system is assured after bubbling ceases, the three-way cock is very carefully turned to air with the buret tip under the mercury surface. The buret mill then be filled with mercury. Once the unit is filled with clean mercury, it may be calibrated by weighing out given amounts of mercury. The buret is filled
1111 with the titrating solution, by immersing the tip and carefully drawing back the spindle by hand. When solutions are changed, the buret should be flushed with several fillings of the new solution to avoid contamination with the previously used solution. Titrations are performed in the usual manner with the tip of the buret below the liquid surface to avoid the effect of surface tension, and stirring may be done by an air stream directed against the buret tip. CALIBRATION
Two instruments were calibrated by weighing out displaced volumes of mercury. One instrument was checked by Albert Hirschman of the Long Island College of Medicine, who obtained an average precision of 0.35 division (equivalent to 0.000035 ml.) expressed as standard deviation based on several measurements of 0.01-ml. displacements. The over-all accuracy of the total titrating capacity of 0.1 ml. was about 0.02% (equivalent to 0.000020 ml.). The other instrument was calibrated by the author, who obtained a standard deviation of 0.50 division average precision and an over-all accuracy of 0.06%. The latter instrument was also calibrated by direct titration of 0.1-ml. portions of 0.001 X sodium hydroxide with 0.01 N hydrochloric acid in the buret. These titrations were carried out by rllbert Hanok of the Brooklyn Jevish Hospital, who investigated the complete range of the instrument. The average of ten determinations gave an over-all accuracy of 0.05% and a standard deviation of 0.11 scale division corresponding to 0.000011 ml. for 0.1-ml. total displacpmpnt ACKNOW LEDGiMEKTS
The suggestions and information concei riirig previoui \I ork offered by Albert Sobel of the Brooklyn Jewish Hospital, and the assistance in calibration extended by Albert Hirschman of the Long Island College of Medicine and Albert Hanok of the Brooklyn Jewish Hospital, are gratefully acknowledged. The assistance of F. Emerson Sparks in designing the base of the buret, and permission from the Emil Greiner Co. to publish this information, are also gratefullv ackriowledged. LITERATURE CITED
Blacet and Leighton, IXD.ENG. CHEM.,ANLL.ED., 3, 267 (1931). Clark and Hermance, Ibid., 9,293 (1937). Conway, Biochem. J . , 28,283 (1934). Cunningham et al., J . Biol. Chem., 139,1 (1941). Dean and Fetcher, Science, 96, 237 (1942). Dusing, Chem. Fabrik,No. 35/36, 313 (1934). Dustman, IND.ENG.CHEM.,ANAL.ED.,4,345 (1932). Emich and Wermuth, “Handbuch der Arbeitsmethoden in der anorganischen Chemie,” Vol. 11, No. 2, p. 671, Berlin and Leipzig, Walter de Gruyter, 1925. Grahame, IND. EXG.CHEM., ANAL.ED., 11, 351 (1939). Hadfield, J . SOC.Chem. Ind.. 61, 45 (1942). Hawes and Skavinski, ISD.EXG.CHEIM., .%NAL. ED., 14, 920 (1942). Keston et al., J . Biol. Chem., 122,227 (1937). Linderstr$ n-Lang and Holter. “Compt. rend. trav.lab. Carlsberg,” 19.No. 4 11931). Ibid.; 19,No. 14 (1933). Lochte and Hoover, ISD.ENG.CHEIM., AXAL.ED.,5, 335 (1933). McFarlane, Ibid.,8,124 (1936). Ogg et al., Ibid., 14,285 (1942). Ormont, 2. anal. Chem., 75, 209 (1928). Rehberg, Biochem. J . , 19,270 (1925). Rosebury and van Heyningen, IXD.ENG.CHEM.,A s . 4 ~ .ED., 14,363 (1942). Scholander, Science. 95,177 (1942). Scholander et al., J . B i d . Chem., 148,495 (1943). Scholander and Evans, Ibid., 169,551 (1947). Seevers and Stormont, IND.EIVG.CHEM.,ASAL. ED., 9, 39 (1937). Standen and Fuller, Ibid., 6, 299 (1934). Titus and Gray, Ibid., 2,370 (1930). Trevan, Lancet, 202,786 (1922). Wyatt. ^Snalyst, 69, 180 (1944). RECEIVED October 23, 1947. Presented before the Division of Analytical and hIicro Chemistry a t the 112th Meeting of the AMERICANCHEMICAL SOCIETY,X e w York, N. Y .
