Ultrafine High-Precision Microburet. Roger Gilniont, Tht! Emil Greiner Co., New York, P;.T.
filling, the orifice opening is not too small to prevent mercury from readily entering.
mcx-precision ultramicroburet of the Soholander type has been described (2,s). The opportunity to verify thestatement that the ultimate limit of sensitivity of such an instrument was far greater than that ai the one described presented itself when
CALIBRATION
Because extremely small volumes of mercury are delivered by the instrument, the usual method of weighing was not feasible. Instead, the instrument was calibrated by direct linear measurement. Two experiments were performed. In the first, the diameter of the extremely small drop of mercury being expelled from the buret tip was measured under the microscope and carrelated against readings on the gage. In the second experiment, the diameter of the drop was measured for tot.al displacement and an average of three determinations was made. In addition, the diameter of the wire was measured both under the microscope and with a sensitive micrometer. The most accurate result was obtained by experiment 1 and the least accurate result by measuring the wire directly. In Table I the results of t,he two experiments are tahulated.
Figure 1. F r o n t Elevation of Ultramioroburet
I
R. W. Gerard ( I ) requested that The Emil Greiner Co. construct an instrument that would be sensitive to loa cubic microns (10-O ml,), In order to reach this sensitivity it wan calculrtted that the plunger would have t o be approximately 0.003 inoh in diameter when used in combination Irith a dial micrometer gage having divisions equal to 0.0001-inch linear traverse. Gages of this sensitivity are commercially avaihble, but for the wire it was necessary to obtain a material that would maintain its stiffness at this comparatively small diameter. After experimenting with tungsten, stainless steel, Xichrome, nickel, and ordinary music wire, it was concluded that music wire was most suitable. Although i t had sufficient stiffness, it was necessary to devise some means of supporting it, so that it would not buckle when entering the &lasscapillary through the rubber gssket.
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CLASS 11.
DESCRIPTION OF APPARATUS
Figure 2.
voir end of the ultramicroburet. Details of the circled portions of this drawing are shown in Figure 2. The music wire is encased in a section of stainless steel tubing, which enters a fine hale in the aluminum bushing as shown in Figure 2, 60 that the wire a t no time during the traverse of the spindle is permitted to buckle. The stainless steel tubing is securely fastened to the spindle of the d i d micrometer gage by means of two Allen head set screws. The glass part of the buret was made from the finest borosilicate glass capillary tubing available, having an internaldiameterof approximately0.25mm. Aridge was blown all around the capillary tubing, so that it could be securely pressed against the silicone rubber gasket by means of hushing and 0 ring. The other end of the capillmy was drawn out to a fine point; a t the tip the diameter of the capillary was reduced to approximately 0.002 inch. The outside of the tube was carefully ground so that the outside diameter a t the very extremity was approximstely 0.010 inch. The silicone rubber gasket was pierced with the music wire to be used as a plunger. Ressonabk care had to he exercised in the assembly. The fully assembled instrument is shown in Figure 3.
Detail of U l t r a m i e m b u r e t
A least square oarrelation ai the data showed that one division of the instrument was equivalent to 1.315 X ml., with a standard deviation of 0.004 X 10-8 ml. As readings can be made to L/m division, the instrument was sensitive to approximately ml. The diameter o f t h e wire was calculated hack from 1X the above figure and shown to be equal to 0.003195 & 0.000005
The buret is filled with mercury in the usual manner. However, special care must be taken because of the extremely small size of the orifice opening a t the tip. A rough calculation shows that it is necessary to apply a pressure of 0.5 atmosphere in order to force mercury through a n orifice of approximately 0.002 inch (0.05 mm.). As a full atmosphere pressure exists a t the time of
F i g u r e 3. 1135
Ultramicroburet
ANALYTICAL CHEMISTRY
1136 Table I.
Calibration of Ultramicroburet
(Total capacity, approximately 10-6 ml.) Reading on Gage Diameter of Drop, Volume, Scale Divisions Mm. A n . x 10Experiment 1. Readings Every 100 Divisions 300 0.150 177 400 0,180 305 418 500 0.200 558 0.220 600 678 0.235 700 822 0.250 800 0.265 900 973 0.275 lo00 1088
From least square correlations: 1 division = 1.315 f 0.004 X 10-8 ml. equivalent to wire of diameter 0.003195 i 0.000005 inch. Actual measured diameter of wire, 0.00318 f 0.00002 inch. Experiment 2. lo00 300
Readings of Total Displacement 0 . 2 8 8 f 0.001 1251 0.185 32 0.001 33 1 920
Blank analyses have shown that the ab~orbentprepared by this method contains only 0.001% or less of carbon dioxide.
-
1 division = 920&10-8 ~
nitrogen-filled “dry box” to protect the product from acidic atmospheric gases. Sodium hydroxide is dissolved in absolute methanol (200 grams per liter) and the solution is saturated with solid barium chloride, When most of the solids have settled, the supernatant liquid is filtered through a sintered-glass funnel. A sufficient amount of this solution is poured over the activated alumina to cover it, but no large excas should be used. Bfter soaking for 15 . minutes, the alcoholic sodium hydroxide is drained off and the impregnated alumina is dried by pumping off the alcohol. Care should be taken to collect the alcohol in a suitable trap cooled by a dry ice-acetone mixture. When no more alcohol can be collected and the dried granules can be shaken easily in the flask, the absorbent is ready for use. Storage in small lots in sealed glass ampoules is recommended.
= 1.314 f 0.013 X 10-s nil
inch, which compares favorably with 0.00318 i O.ooOo2 inch. the actual measured diameter of the wire. The results of experiment 2 are in excellent agreement with those of experiment 1. ACKNOWLEDGMENT
The assistance of F. Emerson Sparks in designing the mechanical features of the instrument and permission from The Emil Greiner Co. to publish this information are gratefully acknowledged. LITERATURE CITED
(1) Gerard, R. W., personal communication. (2) Giimont, R., .ISAL. CHEY.,20, 1109 (1948). (3) Schoiander, P. F., and Evans, H. J., J . B i d . Chenz., 169, 551 (1947). PnEsEsTED before the Divikion of .inalytical Chemistry a t the 11211d .\leeting of the .IMEXIC.AS CHEMICAL SOCIETY, Atlantic City, N.J.
Preparation of a Carbonate-Free Solid Absorbent for Carbon Dioxide. George A. Consolaziol, Charles If’. Chagnon, and Bernard Manning, Geophysics Research Directorate, Air Force Cambridge Research Center, Cambridge, Mass.
LlTERATURE CITED
(I) Dauben, Reid, and Tankwich, ANAL.CEEH, 19,828 (1947).
Fieser, “Experiments in Organic Chemistry.” D. C. Heath & Co., 1941. 13) Keiiey, J . Ind. Eng. Chem., 8 , 1038 (1916) (4) Kdster, Z.anorg. Chem., 13, 134 (1897). (2)
p 360, S e w To1 k,
Laboratory Electric Timing Device. Ralph E. Schachatl and Ernest I. Becker, Chemical Laboratoried, Polytechnic Institute of Brooklyn, Brooklyn 2, N. Y. YTERVITTENT
timers have proved to be very useful in t,he
1-chemistry laboratory for operating total reflux, partial take .
OR,distilling heads ( 2 ) , and other equipment. Such timers have been constructed on a number of principles. Electronic timers operating on a condetwwr discharge principle are typified by those of Fisher (5), Thacker and Walker ( 8 ) ,and that, of Bechtold ( 1 ) as modified by Taylor and Reid ( 7 ) . Kinloch ( 5 ) has recently described an elaborate electronic ratio timer operat,ing on the principle of a relaxation oscillator. Other timers have been designed to drop a switch by mdans of a rotating cam ( 4 , 6). The Scientific Glass .Apparatus Co. makes a timer which operates on an oscillating arm which nukes contact during a selected portion of the oscillating a.rc. The timer described herein operates on t,he following principle: A rotating arm with a terminal contact point runs over an interrupted brass st,rip which may be set “on” or “off” in selected sections to give the desired on-off cycle. The principle is simple, the timer is rugged, easily constructed of inexpettsive and readily ~ ~ _ _ _ 1
Present address, Reinington R a n d , Inc., Bourn Forwalk, Conn.
TORvery
accurate analyses with micro samples of carbon dioxide, or where dilution of radioactive carbon cannot, be tolerated, it has been found necessary to use an absorbent for carbon dioxide which is essentially free from carb0nat.e. Such aellknown absorbents as soda-lime or i\scarite (3) are not usually manufartured from carbonate-free materials and absorb further amount,s of carbon dioxide in storage. Several authors ( I , 4 ) have described the preparation of sodium hydroxide solutions free from carbonate. However, liquid absorbers are not suitable wit,h low temperatures and fast flow rates. The authors have obtained excellent results with a solid absorbent prepared by d e posit,ing carbonate-free sodium hydroxide on activat,ed alumina i n an inert atmosphere such as dry nitrogen.
14
PROCEDURE
The base of the absorbent is activated alumina (8- to 14-mesh). previously boiled in dilute hydrochloric acid. washed several times with freshly boiled distilled water, rinsed with methyl alcohol, and dried in a vacuum desiccator. In order to reduce the water content of the solution as much as possible, absolute methano1 was prepared by dehydration with magnesium turnings a? described by Fieser ( 2 ) . From this point on, all operations should be performed in :i 1
Present address, Watertown Arsenal. Watertown, Mass
1-1 Figure 1. Plane View-of Apparatus
